35 changed files with 67 additions and 2537 deletions
--- a/.forgejo/workflows/release.yml
+++ b/.forgejo/workflows/release.yml
@ -1,14 +1,12 @@
 name: release
 on:
-  push:
+  release:
-    tags:
+    types: [published]
      - '*'
 jobs:
  build:
-    runs-on: ubuntu-latest
+    runs-on: codeberg-small
    container: catthehacker/ubuntu:act-latest
    steps:
      - uses: actions/checkout@v4
@ -37,32 +35,16 @@ jobs:
      - name: Upload to release
        env:
-          FORGEJO_TOKEN: ${{ secrets.FORGEJO_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
-          TAG="${{ github.ref_name }}"
+          RELEASE_ID="${{ github.event.release.id }}"
-          API_BASE="${{ github.server_url }}/api/v1"
+          API_URL="${{ github.api_url }}/repos/${{ github.repository }}/releases/${RELEASE_ID}/assets"
          REPO="${{ github.repository }}"
          # check if release exists
          RELEASE_ID=$(curl -sf \
            -H "Authorization: token ${FORGEJO_TOKEN}" \
            "${API_BASE}/repos/${REPO}/releases/tags/${TAG}" | jq -r '.id // empty')
          if [ -z "$RELEASE_ID" ]; then
            echo "Creating release for ${TAG}..."
            RELEASE_ID=$(curl -sf \
              -H "Authorization: token ${FORGEJO_TOKEN}" \
              -H "Content-Type: application/json" \
              -d '{"tag_name":"'"${TAG}"'","name":"'"${TAG}"'"}' \
              "${API_BASE}/repos/${REPO}/releases" | jq -r '.id')
          fi
          echo "Release ID: ${RELEASE_ID}"
          for file in lofivor-linux-x86_64 lofivor-windows-x86_64.exe; do
            echo "Uploading $file..."
-            curl -sf \
+            curl -X POST \
-              -H "Authorization: token ${FORGEJO_TOKEN}" \
+              -H "Authorization: token ${GITHUB_TOKEN}" \
-              -F "attachment=@${file}" \
+              -H "Content-Type: application/octet-stream" \
-              "${API_BASE}/repos/${REPO}/releases/${RELEASE_ID}/assets?name=${file}"
+              --data-binary @"$file" \
              "${API_URL}?name=${file}"
          done
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@ -10,14 +10,9 @@ jobs:
      matrix:
        include:
          - os: ubuntu-latest
-            target: native
+            artifact: sandbox-linux-x86_64
            artifact: lofivor-linux-x86_64
          - os: ubuntu-latest
            target: x86_64-windows-gnu
            artifact: lofivor-windows-x86_64.exe
          - os: macos-latest
-            target: native
+            artifact: sandbox-macos-aarch64
            artifact: lofivor-macos-aarch64
    runs-on: ${{ matrix.os }}
@ -31,24 +26,12 @@ jobs:
          version: 0.15.2
      - name: Install X11 dependencies (Linux)
-        if: matrix.os == 'ubuntu-latest' && matrix.target == 'native'
+        if: matrix.os == 'ubuntu-latest'
        run: sudo apt-get update && sudo apt-get install -y libx11-dev libxcursor-dev libxrandr-dev libxinerama-dev libxi-dev libxext-dev libxfixes-dev libgl1-mesa-dev
-      - name: Build native
+      - run: zig build -Doptimize=ReleaseFast
        if: matrix.target == 'native'
        run: zig build -Doptimize=ReleaseFast
-      - name: Build cross-compile
+      - run: mv zig-out/bin/sandbox ${{ matrix.artifact }}
        if: matrix.target != 'native'
        run: zig build -Dtarget=${{ matrix.target }} -Doptimize=ReleaseFast
      - name: Rename artifact (Unix)
        if: "!contains(matrix.artifact, '.exe')"
        run: mv zig-out/bin/sandbox ${{ matrix.artifact }}
      - name: Rename artifact (Windows)
        if: contains(matrix.artifact, '.exe')
        run: mv zig-out/bin/sandbox.exe ${{ matrix.artifact }}
      - uses: actions/upload-artifact@v4
        with:
--- a/OPTIMIZATIONS.md
+++ b/OPTIMIZATIONS.md
@ -82,8 +82,8 @@ these target the rendering bottleneck since update loop is already fast.
 | technique              | description                                                          | expected gain                   |
 | ---------------------- | -------------------------------------------------------------------- | ------------------------------- |
-| SSBO instance data     | pack (x, y, color) = 12 bytes instead of 64-byte matrices            | done - see optimization 5       |
+| ~~SSBO instance data~~ | ~~pack (x, y, color) = 12 bytes instead of 64-byte matrices~~        | **done** - see optimization 5   |
-| compute shader updates | move entity positions to GPU entirely, avoid CPU→GPU sync            | done - see optimization 6       |
+| compute shader updates | move entity positions to GPU entirely, avoid CPU→GPU sync            | significant                     |
 | OpenGL vs Vulkan       | test raylib's Vulkan backend                                         | unknown                         |
 | discrete GPU testing   | test on dedicated GPU where instancing/SSBO shine                    | significant (different hw)      |
@ -126,33 +126,6 @@ currently not the bottleneck - update stays <1ms at 100k. these become relevant
 | entity pools          | pre-allocated, reusable entity slots  | reduces allocation overhead |
 | component packing     | minimize struct padding               | better cache utilization    |
 #### estimated gains summary
 | Optimization           | Expected Gain | Why                                               |
 |------------------------|---------------|---------------------------------------------------|
 | SIMD updates           | 0%            | Update already on GPU                             |
 | Multithreaded update   | 0%            | Update already on GPU                             |
 | Cache-friendly layouts | 0%            | CPU doesn't iterate entities                      |
 | Fixed-point math       | 0% or worse   | GPUs are optimized for float                      |
 | SoA vs AoS             | ~5%           | Only helps data upload, not bottleneck            |
 | Frustum culling        | 5-15%         | Most entities converge to center anyway           |
 | LOD rendering          | 20-40%        | Real gains - fewer fragments for distant entities |
 | Temporal techniques    | ~50%          | But with visual artifacts (flickering)            |
 Realistic total if you did everything: ~30-50% improvement
 That'd take you from ~1.4M @ 38fps to maybe ~1.8-2M @ 38fps, or ~1.4M @ 50-55fps.
 What would actually move the needle:
 - GPU-side frustum culling in compute shader (cull before render, not after)
 - Point sprites instead of quads for distant entities (4 vertices → 1)
 - Indirect draw calls (GPU decides what to render, CPU never touches entity data)
 Your real bottleneck is fill rate and vertex throughput on HD 530 integrated
 graphics. The CPU side is already essentially free.
 ---
 ## testing methodology
--- a/README.txt
+++ b/README.txt
@ -4,8 +4,6 @@ lofivor
 sandbox stress test for measuring entity rendering performance on weak hardware.
 written in zig with raylib.
 (lofivor aka lofi-survivor)
 build & run
 -----------
--- a/TODO.md
+++ b/TODO.md
@ -59,7 +59,7 @@ further options (if needed):
 - [x] increase raylib batch buffer (currently 8192 vertices = 2048 quads)
 - [x] GPU instancing (single draw call for all entities)
 - [x] SSBO instance data (12 bytes vs 64-byte matrices)
- [x] compute shader entity updates (raylib supports via rlgl)
+- [ ] compute shader entity updates (if raylib supports)
 - [ ] compare OpenGL vs Vulkan backend
 findings (i5-6500T / HD 530):
@ -68,18 +68,14 @@ findings (i5-6500T / HD 530):
 - instancing doesn't help on integrated graphics (shared RAM, no PCIe savings)
 - bottleneck is memory bandwidth, not draw call overhead
 - rlgl batching is already near-optimal for this hardware
 - compute shaders: update time ~5ms → ~0ms at 150k entities (CPU freed entirely)
-## future optimization concepts (GPU-focused)
+## future optimization concepts
- [ ] GPU-side frustum culling in compute shader
+- [ ] SIMD entity updates (AVX2/SSE)
- [ ] point sprites for distant/small entities (4 verts → 1)
+- [ ] struct-of-arrays vs array-of-structs benchmark
- [ ] indirect draw calls (glDrawArraysIndirect)
+- [ ] multithreaded update loop (thread pool)
-
+- [ ] cache-friendly memory layouts
-## future optimization concepts (CPU - not currently bottleneck)
+- [ ] LOD rendering (skip distant entities or reduce detail)
-
+- [ ] frustum culling (only render visible)
- [ ] SIMD / SoA / multithreading (if game logic makes CPU hot again)
+- [ ] temporal techniques (update subset per frame)
-
+- [ ] fixed-point vs floating-point math
 ## other ideas that aren't about optimization
 - [ ] scanline shader
--- a/build.zig
+++ b/build.zig
@ -4,9 +4,6 @@ pub fn build(b: *std.Build) void {
    const target = b.standardTargetOptions(.{});
    const optimize = b.standardOptimizeOption(.{});
    // tracy profiling (run with -Dtracy=true)
    const enable_tracy = b.option(bool, "tracy", "Enable Tracy profiler") orelse false;
    const raylib_dep = b.dependency("raylib_zig", .{
        .target = target,
        .optimize = optimize,
@ -27,16 +24,6 @@ pub fn build(b: *std.Build) void {
    sandbox_exe.root_module.addImport("raylib", raylib_dep.module("raylib"));
    sandbox_exe.linkLibrary(raylib_dep.artifact("raylib"));
    // tracy integration (optional)
    const ztracy = b.dependency("ztracy", .{
        .enable_ztracy = enable_tracy,
        .on_demand = true, // allow connecting after app starts
    });
    sandbox_exe.root_module.addImport("ztracy", ztracy.module("root"));
    if (enable_tracy) {
        sandbox_exe.linkLibrary(ztracy.artifact("tracy"));
    }
    b.installArtifact(sandbox_exe);
    const sandbox_run_cmd = b.addRunArtifact(sandbox_exe);
--- a/build.zig.zon
+++ b/build.zig.zon
@ -7,10 +7,6 @@
            .url = "git+https://github.com/raylib-zig/raylib-zig#a4d18b2d1cf8fdddec68b5b084535fca0475f466",
            .hash = "raylib_zig-5.6.0-dev-KE8REL5MBQAf3p497t52Xw9P7ojndIkVOWPXnLiLLw2P",
        },
        .ztracy = .{
            .url = "git+https://github.com/zig-gamedev/ztracy?ref=main#e7b401dea9ce006f8b236e3a2ca1a9f3d5c3e896",
            .hash = "ztracy-0.14.0-dev-zHJSq78GGQC904aYvBPn6OOvRVOq_opAwDfeHZdvQyej",
        },
    },
    .paths = .{
        "build.zig",
--- a/docs/GLOSSARY.txt
+++ b/docs/GLOSSARY.txt
@ -1,292 +0,0 @@
 lofivor glossary
 ================
 terms that come up when optimizing graphics.
 clock cycle
 -----------
 one "tick" of the processor's internal clock.
 a CPU or GPU has a crystal oscillator that vibrates at a fixed rate.
 each vibration = one cycle. the processor does some work each cycle.
  1 GHz = 1 billion cycles per second
  1 MHz = 1 million cycles per second
 so a 1 GHz processor has 1 billion opportunities to do work per second.
 "one operation per cycle" is idealized. real work often takes multiple
 cycles (memory access: 100+ cycles, division: 10-20 cycles, add: 1 cycle).
 your HD 530 runs at ~950 MHz, so roughly 950 million cycles per second.
 at 60fps, that's about 15.8 million cycles per frame.
 fill rate
 ---------
 pixels written per second. measured in megapixels/s or gigapixels/s.
  fill rate = ROPs * clock speed * pixels per clock
 your HD 530: 3 ROPs * 950 MHz * 1 = 2.85 GPixels/s theoretical max.
 overdraw
 --------
 drawing the same pixel multiple times per frame.
 if two entities overlap, the back one gets drawn, then the front one
 overwrites it. the back one's work was wasted.
  overdraw ratio = total pixels drawn / screen pixels
 1080p = 2.07M pixels. if you draw 20M pixels, overdraw = ~10x.
 bandwidth
 ---------
 data transfer rate. measured in bytes/second (GB/s, MB/s).
 memory bandwidth = how fast data moves between processor and RAM.
 your HD 530 shares DDR4 with the CPU: ~30 GB/s total.
 a discrete GPU has dedicated VRAM: 200-900 GB/s.
 latency
 -------
 time delay. measured in nanoseconds (ns) or cycles.
 memory latency = time to fetch data from RAM.
  - L1 cache: ~4 cycles
  - L2 cache: ~12 cycles
  - L3 cache: ~40 cycles
  - main RAM: ~200 cycles
 this is why cache matters. a cache miss = 50x slower than a hit.
 throughput vs latency
 ---------------------
 latency = how long ONE thing takes.
 throughput = how many things per second.
 a pipeline can have high latency but high throughput.
 example: a car wash takes 10 minutes (latency).
 but if cars enter every 1 minute, throughput is 60 cars/hour.
 GPUs hide latency with throughput. one thread waits for memory?
 switch to another thread. thousands of threads keep the GPU busy.
 draw call
 ---------
 one command from CPU to GPU: "draw this batch of geometry."
 each draw call has overhead:
  - CPU prepares command buffer
  - driver validates state
  - GPU switches context
 1 draw call for 1M triangles: fast.
 1M draw calls for 1M triangles: slow.
 lofivor uses 1 draw call for all entities (instanced rendering).
 instancing
 ----------
 drawing many copies of the same geometry in one draw call.
 instead of: draw triangle, draw triangle, draw triangle...
 you say: draw this triangle 1 million times, here are the positions.
 the GPU handles the replication. massively more efficient.
 shader
 ------
 a small program that runs on the GPU.
 the name is historical - early shaders calculated shading/lighting.
 but today: a shader is just software running on GPU hardware.
 it doesn't have to do with shading at all.
 more precisely: a shader turns one piece of data into another piece of data.
  - vertex shader: positions → screen coordinates
  - fragment shader: fragments → pixel colors
  - compute shader: data → data (anything)
 GPUs are massively parallel, so shaders run on thousands of inputs at once.
 CPUs have stagnated; GPUs keep getting faster. modern engines like UE5
 increasingly use shaders for work that used to be CPU-only.
 SSBO (shader storage buffer object)
 -----------------------------------
 a block of GPU memory that shaders can read/write.
 unlike uniforms (small, read-only), SSBOs can be large and writable.
 lofivor stores all entity data in an SSBO: positions, velocities, colors.
 compute shader
 --------------
 a shader that does general computation, not rendering.
 runs on GPU cores but doesn't output pixels. just processes data.
 lofivor uses compute shaders to update entity positions.
 because compute exists, shaders can be anything: physics, AI, sorting,
 image processing. the GPU is a general-purpose parallel processor.
 fragment / pixel shader
 -----------------------
 program that runs once per pixel (actually per "fragment").
 determines the final color of each pixel. this is where:
  - texture sampling happens
  - lighting calculations happen
  - the expensive math lives
 lofivor's fragment shader: sample texture, multiply by color. trivial.
 AAA game fragment shader: 500+ instructions. expensive.
 vertex shader
 -------------
 program that runs once per vertex.
 transforms 3D positions to screen positions. lofivor's vertex shader
 reads from SSBO and positions the quad corners.
 ROP (render output unit)
 ------------------------
 final stage of GPU pipeline. writes pixels to framebuffer.
 handles: depth test, stencil test, blending, antialiasing.
 your bottleneck on HD 530. see docs/rops.txt.
 TMU (texture mapping unit)
 --------------------------
 samples textures. reads pixel colors from texture memory.
 your HD 530 has 24 TMUs. they're fast (22.8 GTexels/s).
 texture sampling is cheap relative to ROPs on this hardware.
 EU (execution unit)
 -------------------
 intel's term for shader cores.
 your HD 530 has 24 EUs, each with 8 ALUs = 192 ALUs total.
 these run your vertex, fragment, and compute shaders.
 ALU (arithmetic logic unit)
 ---------------------------
 does math. add, multiply, compare, bitwise operations.
 one ALU can do one operation per cycle (simple ops).
 complex ops (sqrt, sin, cos) take multiple cycles.
 framebuffer
 -----------
 the image being rendered. lives in GPU memory.
 at 1080p with 32-bit color: 1920 * 1080 * 4 = 8.3 MB.
 double-buffered (front + back): 16.6 MB.
 vsync
 -----
 synchronizing frame presentation with monitor refresh.
 without vsync: tearing (half old frame, half new frame).
 with vsync: smooth, but if you miss 16.7ms, you wait for next refresh.
 frame budget
 ------------
 time available per frame.
  60 fps = 16.67 ms per frame
  30 fps = 33.33 ms per frame
 everything (CPU + GPU) must complete within budget or frames drop.
 pipeline stall
 --------------
 GPU waiting for something. bad for performance.
 causes:
  - waiting for memory (cache miss)
  - waiting for previous stage to finish
  - synchronization points (barriers)
  - `discard` in fragment shader (breaks early-z)
 early-z
 -------
 optimization: test depth BEFORE running fragment shader.
 if pixel will be occluded, skip the expensive shader work.
 `discard` breaks this because GPU can't know depth until shader runs.
 LOD (level of detail)
 ---------------------
 using simpler geometry/textures for distant objects.
 far away = fewer pixels = less detail needed.
 saves vertices, texture bandwidth, and fill rate.
 frustum culling
 ---------------
 don't draw what's outside the camera view.
 the "frustum" is the pyramid-shaped visible region.
 anything outside = wasted work. cull it before sending to GPU.
 spatial partitioning
 --------------------
 organizing entities by position for fast queries.
 types: grid, quadtree, octree, BVH.
 "which entities are near point X?" goes from O(n) to O(log n).
 essential for collision detection at scale.
--- a/docs/hd530_optimization_guide.md
+++ b/docs/hd530_optimization_guide.md
@ -1,119 +0,0 @@
 # intel hd 530 optimization guide for lofivor
 based on hardware specs and empirical testing.
 ## hardware constraints
 from `intel_hd_graphics_530.txt`:
 | resource   | value               | implication                                 |
 | ---------- | -------             | -------------                               |
 | ROPs       | 3                   | fill rate limited - this is our ceiling     |
 | TMUs       | 24                  | texture sampling is relatively fast         |
 | memory     | shared DDR4 ~30GB/s | bandwidth is precious, no VRAM              |
 | pixel rate | 2.85 GPixel/s       | max theoretical throughput                  |
 | EUs        | 24 (192 ALUs)       | decent compute, weak vs discrete            |
 | L3 cache   | 768 KB              | small, cache misses hurt                    |
 the bottleneck is ROPs (fill rate), not vertices or compute.
 ## what works (proven)
 ### SSBO instance data
 - 16 bytes per entity vs 64 bytes (matrices)
 - minimizes bandwidth on shared memory bus
 - result: ~5x improvement over instancing
 ### compute shader updates
 - GPU does position/velocity updates
 - no CPU→GPU sync per frame
 - result: update time essentially free
 ### texture sampling
 - 22.8 GTexel/s is fast relative to other units
 - pre-baked circle texture beats procedural math
 - result: 2x faster than procedural fragment shader
 ### instanced triangles/quads
 - most optimized driver path
 - intel mesa heavily optimizes this
 - result: baseline, hard to beat
 ## what doesn't work (proven)
 ### point sprites
 - theoretically 6x fewer vertices
 - reality: 2.4x SLOWER on this hardware
 - triangle rasterizer is more optimized
 - see `docs/point_sprites_experiment.md`
 ### procedural fragment shaders
 - `length()`, `smoothstep()`, `discard` are expensive
 - EUs are weaker than discrete GPUs
 - `discard` breaks early-z optimization
 - result: 3.7x slower than texture sampling
 ### complex fragment math
 - only 24 EUs, each running 8 ALUs
 - transcendentals (sqrt, sin, cos) are 4x slower than FMAD
 - avoid in hot path
 ## what to try next (theoretical)
 ### likely to help
 | technique                            | why it should work                      | expected gain            |
 | -----------                          | -------------------                     | ---------------          |
 | frustum culling (GPU)                | reduce fill rate, which is bottleneck   | 10-30% depending on view |
 | smaller points when zoomed out (LOD) | fewer pixels per entity = less ROP work | 20-40%                   |
 | early-z / depth pre-pass             | skip fragment work for occluded pixels  | moderate                 |
 ### unlikely to help
 | technique                | why it won't help                         |
 | -----------              | ------------------                        |
 | more vertex optimization | already fill rate bound, not vertex bound |
 | SIMD on CPU              | updates already on GPU                    |
 | multithreading           | CPU isn't the bottleneck                  |
 | different vertex layouts | negligible vs fill rate                   |
 ### uncertain (need to test)
 | technique           | notes                                                 |
 | -----------         | -------                                               |
 | vulkan backend      | might have less driver overhead, or might not matter  |
 | indirect draw calls | GPU decides what to render, but we're not CPU bound   |
 | fp16 in shaders     | HD 530 has 2:1 fp16 ratio, might help fragment shader |
 ## key insights
 1. fill rate is king - with only 3 ROPs, everything comes down to how many
   pixels we're writing. optimizations that don't reduce pixel count won't
   help.
 2. shared memory hurts - no dedicated VRAM means CPU and GPU compete for
   bandwidth. keep data transfers minimal.
 3. driver optimization matters - the "common path" (triangles) is more
   optimized than alternatives (points). don't be clever.
 4. texture sampling is cheap - 22.8 GTexel/s is fast. prefer texture
   lookups over ALU math in fragment shaders.
 5. avoid discard - breaks early-z, causes pipeline stalls. alpha blending
   is faster than discard.
 ## current ceiling
 ~950k entities @ 57fps (SSBO + compute + quads)
 to go higher, we need to reduce fill rate:
 - cull offscreen entities
 - reduce entity size when zoomed out
 - or accept lower fps at higher counts
 ## references
 - intel gen9 compute architecture whitepaper
 - empirical benchmarks in `benchmark_current_i56500t.log`
 - point sprites experiment in `docs/point_sprites_experiment.md`
--- a/docs/hysteria.md
+++ b/docs/hysteria.md
@ -1,31 +0,0 @@
 # hysteresis in lofivor
 ## the problem without it
 say your target is 8.33ms. your frame times naturally jitter: 8.2, 8.4, 8.3, 8.5, 8.2...
 without hysteresis, every time it crosses 8.33ms you'd log "crossed threshold!" - potentially dozens of times per second. the log becomes useless noise.
 ## how the code works
 from `sandbox_main.zig` lines 74-89:
 ```
 was_above=false → need frame_ms > 10.33 (target + 2.0 margin) to flip to true
 was_above=true  → need frame_ms < 8.33 (target) to flip back to false
 ```
 this creates a "dead zone" between 8.33 and 10.33ms where no state change happens.
 ## the magnet analogy
 the `was_above_target` boolean is like the magnet's current polarity. the frame time "pushing" past thresholds is like the magnetic field. the key insight: **the threshold you need to cross depends on which side you're currently on.**
 if you're in "good" state, you need a significant spike (>10.33ms) before you flip to "bad". if you're in "bad" state, you only need to drop below 8.33ms to recover. this asymmetry is the hysteresis.
 ## real-world examples
 - thermostat: heat on at 68°F, off at 72°F (prevents rapid on/off cycling)
 - schmitt trigger in electronics: same concept, prevents noise from causing oscillation
 the `THRESHOLD_MARGIN` of 2.0ms is the "width" of the hysteresis band - bigger = more stable but less responsive.
--- a/docs/plans/2025-12-16-zoom-pan-design.md
+++ b/docs/plans/2025-12-16-zoom-pan-design.md
@ -1,54 +0,0 @@
 # Zoom/Pan Camera Design
 A viewport camera for zooming into and panning around the simulation without affecting entity behavior.
 ## Core Behavior
 ### Zoom
 - Scroll wheel zooms toward mouse cursor position
 - Range: 1x (default floor) to 10x (ceiling)
 - Instant response, no animation
 - Esc or Space resets to 1x and clears pan offset
 ### Pan
 - Any mouse button (left/middle/right) + drag pans the viewport
 - Only available when zoom > 1x
 - Bounded to simulation area - cannot pan into empty space
 ### UI
 - Display current zoom level in existing panel under render info (e.g., `zoom: 2.3x`)
 ## Implementation Approach
 ### State
 New camera state in `sandbox_main.zig`:
 ```zig
 var zoom: f32 = 1.0;
 var pan: @Vector(2, f32) = .{ 0, 0 };
 ```
 ### Shader Changes
 Modify `entity.vert` to accept `zoom` and `pan` uniforms:
 - Apply pan offset before converting to NDC
 - Scale by zoom factor
 - Scale quad size by zoom so entities appear larger
 ### Input Handling
 - `getMouseWheelMove()` adjusts zoom (clamped 1.0–10.0)
 - Zoom-toward-cursor: adjust pan to keep point under cursor stationary
 - Mouse drag (any button) adjusts pan with bounds checking
 - Esc/Space resets zoom to 1.0 and pan to (0, 0)
 ### Zoom-Toward-Cursor Math
 When zooming from `oldZoom` to `newZoom` with cursor at `mousePos`:
 ```
 worldMousePos = (mousePos / oldZoom) + pan
 newPan = worldMousePos - (mousePos / newZoom)
 ```
 ### Pan Bounds
 Constrain pan so viewport stays within simulation area:
 ```
 maxPan = simulationSize - (screenSize / zoom)
 pan = clamp(pan, 0, maxPan)
 ```
--- a/docs/plans/2025-12-16-zoom-pan-plan.md
+++ b/docs/plans/2025-12-16-zoom-pan-plan.md
@ -1,440 +0,0 @@
 # Zoom/Pan Camera Implementation Plan
 > **For Claude:** REQUIRED SUB-SKILL: Use superpowers:executing-plans to implement this plan task-by-task.
 **Goal:** Add viewport zoom (scroll wheel toward cursor) and pan (any mouse drag when zoomed) to observe the simulation up close.
 **Architecture:** Camera state (zoom, pan) lives in sandbox_main.zig. Passed to shader as uniforms. All rendering paths use the same camera state, but only SSBO path gets shader-based zoom (others would need separate work).
 **Tech Stack:** Zig, raylib, GLSL 430
 ---
 ### Task 1: Add camera state and shader uniforms
 **Files:**
 - Modify: `src/sandbox_main.zig:266` (add state after `var paused`)
 - Modify: `src/ssbo_renderer.zig:20-21` (add uniform locations to struct)
 - Modify: `src/ssbo_renderer.zig:54-62` (get uniform locations in init)
 - Modify: `src/ssbo_renderer.zig:154-156` (pass uniforms in render)
 **Step 1: Add camera state to sandbox_main.zig**
 After line 266 (`var paused = false;`), add:
 ```zig
 // camera state for zoom/pan
 var zoom: f32 = 1.0;
 var pan = @Vector(2, f32){ 0, 0 };
 ```
 **Step 2: Add uniform locations to SsboRenderer struct**
 In `src/ssbo_renderer.zig`, add to struct fields after line 21 (`circle_texture_loc`):
 ```zig
 zoom_loc: i32,
 pan_loc: i32,
 ```
 **Step 3: Get uniform locations in init**
 After line 55 (`const circle_texture_loc = ...`), add:
 ```zig
 const zoom_loc = rl.gl.rlGetLocationUniform(shader_id, "zoom");
 const pan_loc = rl.gl.rlGetLocationUniform(shader_id, "pan");
 ```
 **Step 4: Add fields to return struct**
 In the return statement (around line 112), add:
 ```zig
 .zoom_loc = zoom_loc,
 .pan_loc = pan_loc,
 ```
 **Step 5: Pass uniforms in render method**
 Change render signature to accept zoom/pan:
 ```zig
 pub fn render(self: *SsboRenderer, entities: *const sandbox.Entities, zoom: f32, pan: @Vector(2, f32)) void {
 ```
 After line 156 (setting screenSize uniform), add:
 ```zig
 // set zoom uniform
 rl.gl.rlSetUniform(self.zoom_loc, &zoom, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_float), 1);
 // set pan uniform
 const pan_arr = [2]f32{ pan[0], pan[1] };
 rl.gl.rlSetUniform(self.pan_loc, &pan_arr, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_vec2), 1);
 ```
 **Step 6: Update render call in sandbox_main.zig**
 Change line 336 from:
 ```zig
 ssbo_renderer.?.render(&entities);
 ```
 To:
 ```zig
 ssbo_renderer.?.render(&entities, zoom, pan);
 ```
 **Step 7: Build and verify compiles**
 Run: `zig build`
 Expected: Compiles with no errors (shader won't use uniforms yet, but that's fine)
 ---
 ### Task 2: Update vertex shader for zoom/pan
 **Files:**
 - Modify: `src/shaders/entity.vert`
 **Step 1: Add uniforms**
 After line 19 (`uniform vec2 screenSize;`), add:
 ```glsl
 uniform float zoom;
 uniform vec2 pan;
 ```
 **Step 2: Update NDC calculation**
 Replace lines 29-31:
 ```glsl
 // convert entity position to NDC
 // entity coords are in screen pixels, convert to [-1, 1]
 float ndcX = (e.x / screenSize.x) * 2.0 - 1.0;
 float ndcY = (e.y / screenSize.y) * 2.0 - 1.0;
 ```
 With:
 ```glsl
 // apply pan offset and zoom to convert to NDC
 // pan is in screen pixels, zoom scales the view
 float ndcX = ((e.x - pan.x) * zoom / screenSize.x) * 2.0 - 1.0;
 float ndcY = ((e.y - pan.y) * zoom / screenSize.y) * 2.0 - 1.0;
 ```
 **Step 3: Scale quad size by zoom**
 Replace line 34:
 ```glsl
 float quadSizeNdc = 16.0 / screenSize.x;
 ```
 With:
 ```glsl
 float quadSizeNdc = (16.0 * zoom) / screenSize.x;
 ```
 **Step 4: Build and test**
 Run: `zig build && ./zig-out/bin/lofivor`
 Expected: Renders exactly as before (zoom=1.0, pan=0,0 should be identical to old behavior)
 ---
 ### Task 3: Add zoom input handling
 **Files:**
 - Modify: `src/sandbox_main.zig` (handleInput function and main loop)
 **Step 1: Add zoom constants**
 After line 32 (BENCH_EXIT_SUSTAIN), add:
 ```zig
 // zoom settings
 const ZOOM_MIN: f32 = 1.0;
 const ZOOM_MAX: f32 = 10.0;
 const ZOOM_SPEED: f32 = 0.1; // multiplier per scroll tick
 ```
 **Step 2: Create handleCamera function**
 After the `handleInput` function (around line 458), add:
 ```zig
 fn handleCamera(zoom: *f32, pan: *@Vector(2, f32)) void {
    const wheel = rl.getMouseWheelMove();
    if (wheel != 0) {
        const mouse_pos = rl.getMousePosition();
        const old_zoom = zoom.*;
        // calculate new zoom
        const zoom_factor = if (wheel > 0) (1.0 + ZOOM_SPEED) else (1.0 / (1.0 + ZOOM_SPEED));
        var new_zoom = old_zoom * zoom_factor;
        new_zoom = std.math.clamp(new_zoom, ZOOM_MIN, ZOOM_MAX);
        if (new_zoom != old_zoom) {
            // zoom toward mouse cursor:
            // keep the world point under the cursor stationary
            // world_pos = (screen_pos / old_zoom) + old_pan
            // new_pan = world_pos - (screen_pos / new_zoom)
            const world_x = (mouse_pos.x / old_zoom) + pan.*[0];
            const world_y = (mouse_pos.y / old_zoom) + pan.*[1];
            pan.*[0] = world_x - (mouse_pos.x / new_zoom);
            pan.*[1] = world_y - (mouse_pos.y / new_zoom);
            zoom.* = new_zoom;
            // clamp pan to bounds
            clampPan(pan, zoom.*);
        }
    }
    // reset on Esc or Space (Space also toggles pause in handleInput)
    if (rl.isKeyPressed(.escape)) {
        zoom.* = 1.0;
        pan.* = @Vector(2, f32){ 0, 0 };
    }
 }
 fn clampPan(pan: *@Vector(2, f32), zoom: f32) void {
    // when zoomed in, limit pan so viewport stays in simulation bounds
    // visible area = screen_size / zoom
    // max pan = world_size - visible_area
    const screen_w: f32 = @floatFromInt(SCREEN_WIDTH);
    const screen_h: f32 = @floatFromInt(SCREEN_HEIGHT);
    const visible_w = screen_w / zoom;
    const visible_h = screen_h / zoom;
    const max_pan_x = @max(0, screen_w - visible_w);
    const max_pan_y = @max(0, screen_h - visible_h);
    pan.*[0] = std.math.clamp(pan.*[0], 0, max_pan_x);
    pan.*[1] = std.math.clamp(pan.*[1], 0, max_pan_y);
 }
 ```
 **Step 3: Call handleCamera in main loop**
 In the main loop, after the `handleInput` call (line 318), add:
 ```zig
 handleCamera(&zoom, &pan);
 ```
 **Step 4: Also reset zoom when Space is pressed**
 In `handleInput`, modify the space key handler (around line 450):
 ```zig
 // pause: space (also resets zoom in handleCamera context)
 if (rl.isKeyPressed(.space)) {
    paused.* = !paused.*;
 }
 ```
 Actually, handleInput doesn't have access to zoom/pan. We need to either:
 - Pass zoom/pan to handleInput
 - Handle space reset in handleCamera
 Let's handle it in handleCamera. Add after the escape check:
 ```zig
 // Space also resets zoom (pause is handled separately in handleInput)
 if (rl.isKeyPressed(.space)) {
    zoom.* = 1.0;
    pan.* = @Vector(2, f32){ 0, 0 };
 }
 ```
 **Step 5: Build and test zoom**
 Run: `zig build && ./zig-out/bin/lofivor`
 Test:
 1. Scroll up - entities should get bigger (zoom in toward cursor)
 2. Scroll down - entities get smaller (but not below 1x)
 3. Press Esc or Space - resets to default view
 ---
 ### Task 4: Add pan input handling
 **Files:**
 - Modify: `src/sandbox_main.zig` (handleCamera function)
 **Step 1: Add pan logic to handleCamera**
 Add this after the zoom handling, before the reset checks:
 ```zig
 // pan with any mouse button drag (only when zoomed in)
 if (zoom.* > 1.0) {
    const any_button = rl.isMouseButtonDown(.left) or
                       rl.isMouseButtonDown(.right) or
                       rl.isMouseButtonDown(.middle);
    if (any_button) {
        const delta = rl.getMouseDelta();
        // pan in opposite direction of drag (drag right = view moves left = pan increases)
        pan.*[0] -= delta.x / zoom.*;
        pan.*[1] -= delta.y / zoom.*;
        clampPan(pan, zoom.*);
    }
 }
 ```
 **Step 2: Build and test pan**
 Run: `zig build && ./zig-out/bin/lofivor`
 Test:
 1. Scroll to zoom in past 1x
 2. Click and drag with any mouse button - viewport should pan
 3. Try to pan past edges - should be bounded
 4. At 1x zoom, dragging should do nothing
 ---
 ### Task 5: Add zoom display to UI
 **Files:**
 - Modify: `src/ui.zig:34` (drawMetrics signature)
 - Modify: `src/ui.zig:71-72` (add zoom line after render)
 - Modify: `src/sandbox_main.zig:387` (pass zoom to drawMetrics)
 **Step 1: Update drawMetrics signature**
 Change line 34:
 ```zig
 pub fn drawMetrics(entities: *const sandbox.Entities, update_us: i64, render_us: i64, paused: bool, font: rl.Font) void {
 ```
 To:
 ```zig
 pub fn drawMetrics(entities: *const sandbox.Entities, update_us: i64, render_us: i64, paused: bool, zoom: f32, font: rl.Font) void {
 ```
 **Step 2: Increase box height for zoom line**
 Change line 50:
 ```zig
 const bg_height: i32 = if (paused) 130 else 100;
 ```
 To:
 ```zig
 const bg_height: i32 = if (paused) 150 else 120;
 ```
 **Step 3: Add zoom display after render line**
 After line 72 (render_text draw), add:
 ```zig
 y += line_height;
 // zoom level
 const zoom_text = std.fmt.bufPrintZ(&buf, "zoom:     {d:.1}x", .{zoom}) catch "?";
 rl.drawTextEx(font, zoom_text, .{ .x = padding, .y = y }, font_size, 0, if (zoom > 1.0) highlight_color else text_color);
 ```
 **Step 4: Update call in sandbox_main.zig**
 Change line 387:
 ```zig
 ui.drawMetrics(&entities, update_time_us, render_time_us, paused, ui_font);
 ```
 To:
 ```zig
 ui.drawMetrics(&entities, update_time_us, render_time_us, paused, zoom, ui_font);
 ```
 **Step 5: Build and test UI**
 Run: `zig build && ./zig-out/bin/lofivor`
 Test:
 1. UI should show "zoom: 1.0x" in white
 2. Scroll to zoom - should update and turn yellow when > 1x
 3. Reset with Esc - back to white 1.0x
 ---
 ### Task 6: Update controls legend
 **Files:**
 - Modify: `src/ui.zig:120-139` (drawControls function)
 **Step 1: Update controls list and box height**
 Change line 121:
 ```zig
 const ctrl_box_height: i32 = @intFromFloat(small_line_height * 5 + box_padding * 2);
 ```
 To:
 ```zig
 const ctrl_box_height: i32 = @intFromFloat(small_line_height * 7 + box_padding * 2);
 ```
 Change the controls array (lines 127-133):
 ```zig
 const controls = [_][]const u8{
    "+/-: 10k entities",
    "shift +/-: 50k",
    "scroll: zoom",
    "drag: pan (zoomed)",
    "space: pause/reset",
    "esc: reset zoom",
    "tab: toggle ui",
 };
 ```
 **Step 2: Build and final test**
 Run: `zig build && ./zig-out/bin/lofivor`
 Full test:
 1. Scroll wheel zooms toward cursor (1x-10x)
 2. Any mouse drag pans when zoomed > 1x
 3. Pan is bounded to simulation area
 4. Esc resets zoom/pan
 5. Space toggles pause AND resets zoom/pan
 6. UI shows zoom level (yellow when zoomed)
 7. Controls legend shows new controls
 ---
 ### Task 7: Commit
 ```bash
 git add src/sandbox_main.zig src/ssbo_renderer.zig src/shaders/entity.vert src/ui.zig
 git commit -m "feat: add zoom/pan camera
 - scroll wheel zooms toward cursor (1x-10x range)
 - any mouse button drag pans when zoomed
 - pan bounded to simulation area
 - esc/space resets to default view
 - zoom level shown in metrics panel"
 ```
--- a/docs/plans/2025-12-17-compute-shader-updates.md
+++ b/docs/plans/2025-12-17-compute-shader-updates.md
@ -1,170 +0,0 @@
 # compute shader entity updates
 move entity position math to GPU, eliminate CPU→GPU sync per frame.
 ## context
 current bottleneck: per-frame `rlUpdateShaderBuffer()` uploads all entity data from CPU to GPU. at 950k entities that's 19MB/frame. targeting 10M entities would be 160MB/frame.
 solution: keep entity data on GPU entirely. compute shader updates positions, vertex shader renders. CPU just dispatches.
 ## data structures
 **GpuEntity (16 bytes, std430):**
 ```glsl
 struct Entity {
    float x;        // world position
    float y;
    int packedVel;  // vx high 16 bits, vy low 16 bits (fixed-point 8.8)
    uint color;     // 0xRRGGBB
 };
 ```
 **zig side:**
 ```zig
 const GpuEntity = extern struct {
    x: f32,
    y: f32,
    packed_vel: i32,
    color: u32,
 };
 fn packVelocity(vx: f32, vy: f32) i32 {
    const vx_fixed: i16 = @intFromFloat(vx * 256.0);
    const vy_fixed: i16 = @intFromFloat(vy * 256.0);
    return (@as(i32, vx_fixed) << 16) | (@as(i32, vy_fixed) & 0xFFFF);
 }
 ```
 ## compute shader
 `src/shaders/entity_update.comp`:
 ```glsl
 #version 430
 layout(local_size_x = 256) in;
 layout(std430, binding = 0) buffer Entities {
    Entity entities[];
 };
 uniform uint entityCount;
 uniform uint frameNumber;
 uniform vec2 screenSize;
 uniform vec2 center;
 uniform float respawnRadius;
 void main() {
    uint id = gl_GlobalInvocationID.x;
    if (id >= entityCount) return;
    Entity e = entities[id];
    // unpack velocity
    float vx = float(e.packedVel >> 16) / 256.0;
    float vy = float((e.packedVel << 16) >> 16) / 256.0;
    // update position
    e.x += vx;
    e.y += vy;
    // respawn check
    float dx = e.x - center.x;
    float dy = e.y - center.y;
    if (dx*dx + dy*dy < respawnRadius * respawnRadius) {
        // GPU RNG
        uint seed = id * 1103515245u + frameNumber * 12345u;
        seed = seed * 747796405u + 2891336453u;
        uint edge = seed & 3u;
        float t = float((seed >> 2) & 0xFFFFu) / 65535.0;
        // spawn on edge with velocity toward center
        // (full edge logic in implementation)
    }
    entities[id] = e;
 }
 ```
 ## integration
 raylib doesn't wrap compute shaders. use raw GL calls via `compute.zig`:
 ```zig
 pub fn dispatch(entity_count: u32, frame: u32) void {
    gl.glUseProgram(program);
    gl.glUniform1ui(entity_count_loc, entity_count);
    gl.glUniform1ui(frame_loc, frame);
    // ... other uniforms
    const groups = (entity_count + 255) / 256;
    gl.glDispatchCompute(groups, 1, 1);
    gl.glMemoryBarrier(gl.GL_SHADER_STORAGE_BARRIER_BIT);
 }
 ```
 ## frame flow
 **before:**
 ```
 CPU: update positions (5ms at 950k)
 CPU: copy to gpu_buffer
 CPU→GPU: rlUpdateShaderBuffer() ← bottleneck
 GPU: render
 ```
 **after:**
 ```
 GPU: compute dispatch (~0ms CPU time)
 GPU: memory barrier
 GPU: render
 ```
 ## implementation steps
 each step is a commit point if desired.
 ### step 1: GpuEntity struct expansion
 - modify `GpuEntity` in sandbox.zig: add `packed_vel` field
 - add `packVelocity()` helper
 - update ssbo_renderer to handle 16-byte stride
 - verify existing rendering still works
 ### step 2: compute shader infrastructure
 - create `src/compute.zig` with GL bindings
 - create `src/shaders/entity_update.comp` (position update only, no respawn yet)
 - load and compile compute shader in sandbox_main.zig
 - dispatch before render, verify positions update
 ### step 3: respawn logic
 - add GPU RNG to compute shader
 - implement edge spawning + velocity calculation
 - remove CPU update loop from sandbox.zig
 ### step 4: cleanup ✓
 - `--compute` is now default, `--cpu` flag for fallback/comparison
 - justfile updated: `just bench` (compute), `just bench-cpu` (comparison)
 - verbose debug output reduced
 ## files changed
 **new:**
 - `src/shaders/entity_update.comp`
 - `src/compute.zig`
 **modified:**
 - `src/sandbox.zig` — GpuEntity struct, packVelocity(), remove CPU update
 - `src/ssbo_renderer.zig` — remove per-frame upload
 - `src/sandbox_main.zig` — init compute, dispatch in frame loop
 ## risks
 1. **driver quirks** — intel HD 530 compute support is fine but older, may hit edge cases
 2. **debugging** — GPU code harder to debug, start with small counts
 3. **fallback** — keep `--compute` flag to A/B test against existing SSBO path
 ## expected results
 - CPU update time: ~5ms → ~0ms
 - no per-frame buffer upload
 - target: 1M+ entities, pushing toward 10M ceiling
--- a/docs/point_sprites_experiment.md
+++ b/docs/point_sprites_experiment.md
@ -1,89 +0,0 @@
 # point sprites experiment
 branch: `point-sprites` (point-sprites work)
 date: 2024-12
 hardware: intel hd 530 (skylake gt2, i5-6500T)
 ## hypothesis
 point sprites should be faster than quads because:
 - 1 vertex per entity instead of 6 (quad = 2 triangles)
 - less vertex throughput
 - `gl_PointCoord` provides texture coords automatically
 ## implementation
 ### vertex shader changes
 - removed quad vertex attributes (position, texcoord)
 - use `gl_PointSize = 16.0 * zoom` for size control
 - position calculated from SSBO data only
 ### fragment shader changes
 - use `gl_PointCoord` instead of vertex texcoord
 - sample circle texture for alpha
 ### renderer changes
 - load `glEnable` and `glDrawArraysInstanced` via `rlGetProcAddress`
 - enable `GL_PROGRAM_POINT_SIZE`
 - draw with `glDrawArraysInstanced(GL_POINTS, 0, 1, count)`
 - removed VBO (no vertex data needed)
 ## results
 ### attempt 1: procedural circle in fragment shader
 ```glsl
 vec2 coord = gl_PointCoord - vec2(0.5);
 float dist = length(coord);
 float alpha = 1.0 - smoothstep(0.4, 0.5, dist);
 if (alpha < 0.01) discard;
 ```
 **benchmark @ 350k entities:**
 - point sprites: 23ms render, 43fps
 - quads (main): 6.2ms render, 151fps
 - **result: 3.7x SLOWER**
 **why:** `discard` breaks early-z optimization, `length()` and `smoothstep()` are ALU-heavy, intel integrated GPUs are weak at fragment shader math.
 ### attempt 2: texture sampling
 ```glsl
 float alpha = texture(circleTexture, gl_PointCoord).r;
 finalColor = vec4(fragColor, alpha);
 ```
 **benchmark @ 450k entities:**
 - point sprites: 19.1ms render, 52fps
 - quads (main): 8.0ms render, 122fps
 - **result: 2.4x SLOWER**
 better than procedural, but still significantly slower than quads.
 ## analysis
 the theoretical advantage (1/6 vertices) doesn't translate to real performance because:
 1. **triangle path is more optimized** - intel's driver heavily optimizes the standard triangle rasterization path. point sprites use a less-traveled code path.
 2. **fill rate is the bottleneck** - HD 530 has only 3 ROPs. we're bound by how fast we can write pixels, not by vertex count. reducing vertices from 6 to 1 doesn't help when fill rate is the constraint.
 3. **point size overhead** - each point requires computing `gl_PointSize` and setting up the point sprite rasterization, which may have per-vertex overhead.
 4. **texture cache behavior** - `gl_PointCoord` may have worse cache locality than explicit vertex texcoords.
 ## conclusion
 **point sprites are a regression on intel hd 530.**
 the optimization makes theoretical sense but fails in practice on this hardware. the quad/triangle path is simply more optimized in intel's mesa driver.
 **keep this branch for testing on discrete GPUs** where point sprites might actually help (nvidia/amd have different optimization priorities).
 ## lessons learned
 1. always benchmark, don't assume
 2. "fewer vertices" doesn't always mean faster
 3. integrated GPU optimization is different from discrete
 4. the most optimized path is usually the most common path (triangles)
 5. fill rate matters more than vertex count at high entity counts
--- a/docs/rops.txt
+++ b/docs/rops.txt
@ -1,201 +0,0 @@
 rops: render output units
 =========================
 what they are, where they came from, and what yours can do.
 what is a rop?
 --------------
 ROP = Render Output Unit (originally "Raster Operations Pipeline")
 it's the final stage of the GPU pipeline. after all the fancy shader
 math is done, the ROP is the unit that actually writes pixels to memory.
 think of it as the bottleneck between "calculated" and "visible."
 a ROP does:
  - depth testing (is this pixel in front of what's already there?)
  - stencil testing (mask operations)
  - blending (alpha, additive, etc)
  - anti-aliasing resolve
  - writing the final color to the framebuffer
 one ROP can write one pixel per clock cycle (roughly).
 the first rop
 -------------
 the term comes from the IBM 8514/A (1987), which had dedicated hardware
 for "raster operations" - bitwise operations on pixels (AND, OR, XOR).
 this was revolutionary because before this, the CPU did all pixel math.
 but the modern ROP as we know it emerged with:
  NVIDIA NV1 (1995)
    one of the first chips with dedicated pixel output hardware
    could do ~1 million textured pixels/second
  3dfx Voodoo (1996)
    the card that defined the modern GPU pipeline
    had 1 TMU + 1 pixel pipeline (essentially 1 ROP)
    could push 45 million pixels/second
    that ONE pipeline ran Quake at 640x480
  NVIDIA GeForce 256 (1999)
    "the first GPU" - named itself with that term
    4 pixel pipelines = 4 ROPs
    480 million pixels/second
 so the original consumer 3D cards had... 1 ROP. and they ran Quake.
 what one rop can do
 -------------------
 let's do the math.
 one ROP at 100 MHz (3dfx Voodoo era):
  100 million cycles/second
  ~1 pixel per cycle
  = 100 megapixels/second
 at 640x480 @ 60fps:
  640 * 480 * 60 = 18.4 megapixels/second needed
 so ONE ROP at 100MHz could handle 640x480 with ~5x headroom for overdraw.
 at 1024x768 @ 60fps:
  1024 * 768 * 60 = 47 megapixels/second
 now you're at 2x overdraw max. still playable, but tight.
 one modern rop
 --------------
 a single modern ROP runs at ~1-2 GHz and can do more per cycle:
  - multiple color outputs (MRT)
  - 64-bit or 128-bit color formats
  - compressed writes
 rough estimate for one ROP at 1.5 GHz:
  ~1.5 billion pixels/second base throughput
 at 1920x1080 @ 60fps:
  1920 * 1080 * 60 = 124 megapixels/second
 one ROP could handle 1080p with 12x overdraw headroom.
 at 4K @ 60fps:
  3840 * 2160 * 60 = 497 megapixels/second
 one ROP could handle 4K with 3x overdraw. tight, but possible.
 your three rops (intel hd 530)
 ------------------------------
 HD 530 specs:
  - 3 ROPs
  - ~950 MHz boost clock
  - theoretical: 2.85 GPixels/second
 let's break that down:
 at 1080p @ 60fps (124 MP/s needed):
  2850 / 124 = 23x overdraw budget
 that's actually generous! you could draw each pixel 23 times.
 so why does lofivor struggle at 1M entities?
 because 1M entities at 4x4 pixels = 16M pixels minimum.
 but with overlap? let's say average 10x overdraw:
  160M pixels/frame
  at 60fps = 9.6 billion pixels/second
 your ceiling is 2.85 billion.
 so you're 3.4x over budget. that's why you top out around 300k-400k
 before frame drops (which matches empirical testing).
 the real constraint
 -------------------
 ROPs don't work in isolation. they're limited by:
  1. MEMORY BANDWIDTH
     each pixel write = memory access
     HD 530 shares DDR4 with CPU (~30 GB/s)
     at 32-bit color: 30GB/s / 4 bytes = 7.5 billion pixels/second max
     but you're competing with CPU, texture reads, etc.
     realistic: maybe 2-3 billion pixels for framebuffer writes
  2. TEXTURE SAMPLING
     if fragment shader samples textures, TMUs must keep up
     HD 530 has 24 TMUs, so this isn't the bottleneck
  3. SHADER EXECUTION
     ROPs wait for fragments to be shaded
     if shaders are slow, ROPs starve
     lofivor's shaders are trivial, so this isn't the bottleneck
 for lofivor specifically: your 3 ROPs are THE ceiling.
 what could you do with more rops?
 ---------------------------------
 comparison:
  Intel HD 530:     3 ROPs,  2.85 GPixels/s
  GTX 1060:        48 ROPs,  72 GPixels/s
  RTX 3080:        96 ROPs, 164 GPixels/s
  RTX 4090:       176 ROPs, 443 GPixels/s
 with a GTX 1060 (25x your fill rate):
  lofivor could probably hit 5-10 million entities
 with an RTX 4090 (155x your fill rate):
  tens of millions, limited by other factors
 perspective: what 3 rops means historically
 -------------------------------------------
 your HD 530 has roughly the fill rate of:
  - GeForce 4 Ti 4600 (2002): 4 ROPs, 1.2 GPixels/s
  - Radeon 9700 Pro (2002): 8 ROPs, 2.6 GPixels/s
 you're running hardware that, in raw pixel output, matches GPUs from
 20+ years ago. but with modern features (compute shaders, SSBO, etc).
 this is why lofivor is interesting: you're achieving 700k+ entities
 on fill-rate-equivalent hardware that originally ran games with
 maybe 10,000 triangles on screen.
 the difference is technique. those 2002 games did complex per-pixel
 lighting, shadows, multiple texture passes. lofivor does one texture
 sample and one blend. same fill rate, 100x the entities.
 the lesson
 ----------
 ROPs are simple: they write pixels.
 the number you have determines your pixel budget.
 everything else (shaders, vertices, CPU logic) only matters if
 the ROPs aren't your bottleneck.
 with 3 ROPs, you have roughly 2.85 billion pixels/second.
 spend them wisely:
  - cull what's offscreen (don't spend pixels on invisible things)
  - shrink distant objects (LOD saves pixels)
  - reduce overlap (spatial organization)
  - keep shaders simple (don't starve the ROPs)
 your 3 ROPs can do remarkable things. Quake ran on 1.
--- a/docs/why-millions-is-hard.txt
+++ b/docs/why-millions-is-hard.txt
@ -1,316 +0,0 @@
 why rendering millions of entities is hard
 =========================================
 and what "hard" actually means, from first principles.
 the simple answer
 -----------------
 every frame, your computer does work. work takes time. you have 16.7
 milliseconds to do all the work before the next frame (at 60fps).
 if the work takes longer than 16.7ms, you miss the deadline. frames drop.
 the game stutters.
 10 million entities means 10 million units of work. whether that fits in
 16.7ms depends on how much work each unit is.
 what is "work" anyway?
 ----------------------
 let's trace what happens when you draw one entity:
  1. CPU: "here's an entity at position (340, 512), color cyan"
  2. that data travels over a bus to the GPU
  3. GPU: receives the data, stores it in memory
  4. GPU: runs a vertex shader (figures out where on screen)
  5. GPU: runs a fragment shader (figures out what color each pixel is)
  6. GPU: writes pixels to the framebuffer
  7. framebuffer gets sent to your monitor
 each step has a speed limit. the slowest step is your bottleneck.
 the bottlenecks, explained simply
 ---------------------------------
 MEMORY BANDWIDTH
  how fast data can move around. measured in GB/s.
  think of it like a highway. you can have a fast car (processor), but
  if the highway is jammed, you're stuck in traffic.
  an integrated GPU (like Intel HD 530) shares the highway with the CPU.
  a discrete GPU (like an RTX card) has its own private highway.
  this is why lofivor's SSBO optimization helped so much: shrinking
  entity data from 64 bytes to 12 bytes means 5x less traffic.
 DRAW CALLS
  every time you say "GPU, draw this thing", there's overhead.
  the CPU and GPU have to synchronize, state gets set up, etc.
  1 draw call for 1 million entities: fast
  1 million draw calls for 1 million entities: slow
  this is why batching matters. not the drawing itself, but the
  *coordination* of drawing.
 FILL RATE
  how many pixels the GPU can color per second.
  a 4x4 pixel entity = 16 pixels
  1 million entities = 16 million pixels minimum
  but your screen is only ~2 million pixels (1920x1080). so entities
  overlap. "overdraw" means coloring the same pixel multiple times.
  10 million overlapping entities might touch each pixel 50+ times.
  that's 100 million pixel operations.
 SHADER COMPLEXITY
  the GPU runs a tiny program for each vertex and each pixel.
  simple: "put it here, color it this" = fast
  complex: "calculate lighting from 8 sources, sample 4 textures,
           apply normal mapping, do fresnel..." = slow
  lofivor's shaders are trivial. AAA game shaders are not.
 CPU-GPU SYNCHRONIZATION
  the CPU and GPU work in parallel, but sometimes they have to wait
  for each other.
  if the CPU needs to read GPU results, it stalls.
  if the GPU needs new data and the CPU is busy, it stalls.
  good code keeps them both busy without waiting.
 why "real games" hit CPU walls
 ------------------------------
 rendering is just putting colors on pixels. that's the GPU's job.
 but games aren't just rendering. they're also:
  - COLLISION DETECTION
    does entity A overlap entity B?
    naive approach: check every pair
    1,000 entities = 500,000 checks (n squared / 2)
    10,000 entities = 50,000,000 checks
    1,000,000 entities = 500,000,000,000,000 checks
    that's 500 trillion. per frame. not happening.
    smart approach: spatial partitioning (grids, quadtrees)
    only check nearby entities. but still, at millions of entities,
    even "nearby" is a lot.
  - AI / BEHAVIOR
    each entity decides what to do.
    simple: move toward player. cheap.
    complex: pathfind around obstacles, consider threats, coordinate
             with allies, remember state. expensive.
    lofivor entities just drift in a direction. no decisions.
    a real game enemy makes decisions every frame.
  - PHYSICS
    entities push each other, bounce, have mass and friction.
    every interaction is math. lots of entities = lots of math.
  - GAME LOGIC
    damage calculations, spawning, leveling, cooldowns, buffs...
    all of this runs on the CPU, every frame.
 so: lofivor can render 700k entities because they don't DO anything.
 a game with 700k entities that think, collide, and interact would
 need god-tier optimization or would simply not run.
 what makes AAA games slow on old hardware?
 ------------------------------------------
 it's not entity count. most AAA games have maybe hundreds of
 "entities" on screen. it's everything else:
  TEXTURE RESOLUTION
    a 4K texture is 67 million pixels of data. per texture.
    one character might have 10+ textures (diffuse, normal, specular,
    roughness, ambient occlusion...).
    old hardware: less VRAM, slower texture sampling.
  SHADER COMPLEXITY
    modern materials simulate light physics. subsurface scattering,
    global illumination, ray-traced reflections.
    each pixel might do hundreds of math operations.
  POST-PROCESSING
    bloom, motion blur, depth of field, ambient occlusion, anti-aliasing.
    full-screen passes that touch every pixel multiple times.
  MESH COMPLEXITY
    a character might be 100,000 triangles.
    10 characters = 1 million triangles.
    each triangle goes through the vertex shader.
  SHADOWS
    render the scene again from the light's perspective.
    for each light. every frame.
 AAA games are doing 100x more work per pixel than lofivor.
 lofivor is doing 100x more pixels than AAA games.
 different problems.
 the "abuse" vs "respect" distinction
 ------------------------------------
 abuse: making the hardware do unnecessary work.
 respect: achieving your goal with minimal waste.
 examples of abuse (that lofivor fixed):
  - sending 64 bytes (a full matrix) when you need 12 bytes (x, y, color)
  - one draw call per entity when you could batch
  - calculating transforms on CPU when GPU could do it
  - clearing the screen twice
  - uploading the same data every frame
 examples of abuse in the wild:
  - electron apps using a whole browser to show a chat window
  - games that re-render static UI every frame
  - loading 4K textures for objects that appear 20 pixels tall
  - running AI pathfinding for off-screen entities
 the hardware has limits. respecting them means fitting your game
 within those limits through smart decisions. abusing them means
 throwing cycles at problems you created yourself.
 so can you do 1 million entities with juice on old hardware?
 ------------------------------------------------------------
 yes, with the right decisions.
 what "juice" typically means:
  - screen shake (free, just offset the camera)
  - particle effects (separate system, heavily optimized)
  - flash/hit feedback (change a color value)
  - sound (different system entirely)
 particles are special: they're designed for millions of tiny things.
 they don't collide, don't think, often don't even persist (spawn,
 drift, fade, die). GPU particle systems are essentially what lofivor
 became: minimal data, instanced rendering.
 what would kill you at 1 million:
  - per-entity collision
  - per-entity AI
  - per-entity sprite variety (texture switches)
  - per-entity complex shaders
 what you could do:
  - 1 million particles (visual only, no logic)
  - 10,000 enemies with collision/AI + 990,000 particles
  - 100,000 enemies with simple behavior + spatial hash collision
 the secret: most of what looks like "millions of things" in games
 is actually a small number of meaningful entities + a large number
 of dumb particles.
 the laws of physics (sort of)
 -----------------------------
 there are hard limits:
  MEMORY BUS BANDWIDTH
    a DDR4 system might move 25 GB/s.
    1 million entities at 12 bytes each = 12 MB.
    at 60fps = 720 MB/s just for entity data.
    that's only 3% of bandwidth. plenty of room.
    but a naive approach (64 bytes, plus overhead) could be
    10x worse. suddenly you're at 30%.
  CLOCK CYCLES
    a 3GHz CPU does 3 billion operations per second.
    at 60fps, that's 50 million operations per frame.
    1 million entities = 50 operations each.
    50 operations is: a few multiplies, some loads/stores, a branch.
    that's barely enough for "move in a direction".
    pathfinding? AI? collision? not a chance.
  PARALLELISM
    GPUs have thousands of cores but they're simple.
    CPUs have few cores but they're smart.
    entity rendering: perfectly parallel (GPU wins)
    entity decision-making: often sequential (CPU bound)
 so yes, physics constrains us. but "physics" here means:
  - how fast electrons move through silicon
  - how much data fits on a wire
  - how many transistors fit on a chip
 within those limits, there's room. lots of room, if you're clever.
 lofivor went from 5k to 700k by being clever, not by breaking physics.
 the actual lesson
 -----------------
 the limit isn't really "the hardware can't do it."
 the limit is "the hardware can't do it THE WAY YOU'RE DOING IT."
 every optimization in lofivor was finding a different way:
  - don't draw circles, blit textures
  - don't call functions, submit vertices directly
  - don't send matrices, send packed structs
  - don't update on CPU, use compute shaders
 the hardware was always capable of 700k. the code wasn't asking right.
 this is true at every level. that old laptop struggling with 10k
 entities in some game? probably not the laptop's fault. probably
 the game is doing something wasteful that doesn't need to be.
 "runs poorly on old hardware" often means "we didn't try to make
 it run on old hardware" not "it's impossible on old hardware."
 closing thought
 ---------------
 10 million is a lot. but 1 million? 2 million?
 with discipline: yes.
 with decisions that respect the hardware: yes.
 with awareness of what's actually expensive: yes.
 the knowledge of what's expensive is the key.
 most developers don't have it. they use high-level abstractions
 that hide the cost. they've never seen a frame budget or a
 bandwidth calculation.
 lofivor is a learning tool. the journey from 5k to 700k teaches
 where the costs are. once you see them, you can't unsee them.
 you start asking: "what is this actually doing? what does it cost?
 is there a cheaper way?"
 that's the skill. not the specific techniques—those change with
 hardware. the skill is asking the questions.
--- a/journal.txt
+++ b/journal.txt
@ -206,38 +206,3 @@ total improvement from baseline:
 - SSBO: 60fps @ ~700k entities
 - ~140x improvement overall!
 ---
 optimization 6: compute shader updates
 --------------------------------------
 technique: move entity position + respawn logic from CPU to GPU compute shader
 code: compute.zig, shaders/entity_update.comp, ssbo_renderer.zig
 version: 0.7.0
 struct GpuEntity {
    x: f32,        // 4 bytes
    y: f32,        // 4 bytes
    packed_vel: i32, // 4 bytes (vx/vy in fixed-point 8.8)
    color: u32,    // 4 bytes
 };                 // = 16 bytes total (was 12)
 changes:
 - entity_update.comp: position update, center check, edge respawn, velocity calc
 - GPU RNG: PCG-style PRNG seeded with entity id + frame number
 - ssbo_renderer: renderComputeMode() only uploads NEW entities (when count grows)
 - CPU update loop skipped entirely when compute enabled
 benchmark results (i5-6500T / HD 530):
 - update time: ~5ms → ~0ms at 150k entities
 - render time unchanged (GPU-bound as before)
 - total frame time improvement at high entity counts
 analysis: CPU was doing ~150k position updates + distance checks + respawn logic
 per frame. now GPU does it in parallel via 256-thread workgroups. CPU only uploads
 new entities when user adds them, not per-frame. memory barrier ensures compute
 writes visible to vertex shader before draw.
 flags:
 - --compute: GPU compute updates (now default)
 - --cpu: fallback to CPU update path for comparison
--- a/16
+++ b/16
@ -42,20 +42,11 @@ check:
 test:
    zig build test
-# run sandbox (GPU compute is default)
+# auto-benchmark (ramps entities until performance degrades, works on linux/windows)
 sandbox:
    zig build -Doptimize=ReleaseFast run
 # auto-benchmark (ramps entities until performance degrades)
 bench:
    zig build -Doptimize=ReleaseFast run -- --bench
    cat benchmark.log
 # benchmark with CPU update path (for comparison)
 bench-cpu:
    zig build -Doptimize=ReleaseFast run -- --bench --cpu
    cat benchmark.log
 # software-rendered benchmark (for CI/headless servers)
 [linux]
 bench-sw:
@ -67,8 +58,3 @@ bench-sw:
 bench-sw:
    @echo "bench-sw: windows doesn't have xvfb equivalent"
    @echo "use 'just bench' if you have a GPU, or run in WSL/linux CI"
 [linux]
 profile port="9876":
  # start Tracy: tracy-profiler -a 127.0.0.1 -p {{port}}
  zig build -Dtracy=true -Doptimize=ReleaseFast && TRACY_PORT={{port}} ./zig-out/bin/sandbox
--- a/releases/0.1.0-unoptimized.txt
+++ b/releases/0.1.0-unoptimized.txt
@ -1,8 +0,0 @@
 the baseline: one draw call per entity, pure and simple
 - individual rl.drawCircle() calls in a loop
 - ~5k entities at 60fps before frame times tank
 - linear scaling: 10k = ~43ms, 20k = ~77ms
 - render-bound (update loop stays under 1ms even at 30k)
 - each circle is its own GPU draw call
 - the starting point for optimization experiments
--- a/releases/0.2.0-texture_blitting.txt
+++ b/releases/0.2.0-texture_blitting.txt
@ -1,8 +0,0 @@
 pre-render once, blit many: 10x improvement
 - render circle to 16x16 texture at startup
 - drawTexture() per entity instead of drawCircle()
 - raylib batches same-texture draws internally
 - ~50k entities at 60fps
 - simple change, big win
 - still one function call per entity, but GPU work is batched
--- a/releases/0.3.0-quad_batching.txt
+++ b/releases/0.3.0-quad_batching.txt
@ -1,9 +0,0 @@
 bypass the wrapper, go straight to rlgl: 2x more
 - skip drawTexture(), submit vertices directly via rl.gl
 - manually build quads: rlTexCoord2f + rlVertex2f per corner
 - rlBegin/rlEnd wraps the whole entity loop
 - ~100k entities at 60fps
 - eliminates per-call function overhead
 - vertices go straight to GPU buffer
 - 20x improvement over baseline
--- a/releases/0.3.1-batch_buffer.txt
+++ b/releases/0.3.1-batch_buffer.txt
@ -1,11 +0,0 @@
 bigger buffer, fewer flushes: squeezing out more headroom
 - increased raylib batch buffer from 8192 to 32768 vertices
 - ~140k entities at 60fps on i5-6500T
 - ~40% improvement over default buffer
 - fewer GPU flushes per frame
 - also added: release workflows for github and forgejo
 - added OPTIMIZATIONS.md documenting the journey
 - added README, UI panel with FPS display
 - heap allocated entity array to support 1 million entities
 - per-entity RGB colors
--- a/releases/0.4.0-gpu_instancing.txt
+++ b/releases/0.4.0-gpu_instancing.txt
@ -1,13 +0,0 @@
 gpu instancing: a disappointing discovery
 - drawMeshInstanced() with per-entity transform matrices
 - ~150k entities at 60fps - barely better than rlgl batching
 - negligible improvement on integrated graphics
 - why it didn't help:
  - integrated GPU shares system RAM (no PCIe transfer savings)
  - 64-byte matrix per entity vs ~80 bytes for rlgl vertices
  - bottleneck is memory bandwidth, not draw call overhead
  - rlgl batching already minimizes draw calls effectively
 - orthographic camera setup for 2D-like rendering
 - heap-allocated transforms buffer (64MB too big for stack)
 - lesson learned: not all "advanced" techniques are wins
--- a/releases/0.5.0-ssbo_instancing.txt
+++ b/releases/0.5.0-ssbo_instancing.txt
@ -1,17 +0,0 @@
 ssbo breakthrough: 5x gain by shrinking the data
 - pack entity data (x, y, color) into 12-byte struct
 - upload via shader storage buffer object (SSBO)
 - ~700k entities at 60fps (i5-6500T / HD 530)
 - ~950k entities at ~57fps
 - 5x improvement over previous best
 - 140x total from baseline
 - why it works:
  - 12 bytes vs 64 bytes (matrices) = 5.3x less bandwidth
  - 12 bytes vs 80 bytes (rlgl vertices) = 6.7x less bandwidth
  - no CPU-side matrix calculations
  - GPU does NDC conversion and color unpacking
 - custom vertex/fragment shaders
 - single rlDrawVertexArrayInstanced() call for all entities
 - shaders embedded at build time
 - removed FPS cap, added optional vsync arg
--- a/releases/0.5.1-windows_build.txt
+++ b/releases/0.5.1-windows_build.txt
@ -1,5 +0,0 @@
 cross-platform release: adding windows to the party
 - updated github release workflow
 - builds for both linux and windows now
 - no code changes, just CI/CD work
--- a/releases/0.6.0-zoom_zoom.txt
+++ b/releases/0.6.0-zoom_zoom.txt
@ -1,10 +0,0 @@
 zoom and pan: making millions of entities explorable
 - mouse wheel zoom
 - click and drag panning
 - orthographic camera transforms
 - memory panel showing entity buffer sizes
 - background draws immediately (no flicker)
 - tab key toggles UI panels
 - explained "lofivor" name in README (lo-fi survivor)
 - shader updated for zoom/pan transforms
--- a/releases/0.6.1-q_to_quit.txt
+++ b/releases/0.6.1-q_to_quit.txt
@ -1,5 +0,0 @@
 quick exit: zoom out then quit
 - q key first zooms out, second press quits
 - nice way to see the full entity field before closing
 - minor UI text fix
--- a/releases/0.7.0-compute_shader.txt
+++ b/releases/0.7.0-compute_shader.txt
@ -1,11 +0,0 @@
 compute shader: moving physics to the GPU
 - entity position updates now run on GPU via compute shader
 - GPU-based RNG for entity velocity randomization
 - full simulation loop stays on GPU, no CPU roundtrip
 - new compute.zig module for shader management
 - GpuEntity struct with position, velocity, and color
 - tracy profiling integration
 - FPS display turns green (good) or red (bad)
 - added design docs for zoom/pan and compute shader work
 - cross-platform alignment fixes for shader data
--- a/src/compute.zig
+++ b/src/compute.zig
@ -1,111 +0,0 @@
 // compute shader module for GPU entity updates
 // wraps raw GL calls that raylib doesn't expose directly
 const std = @import("std");
 const rl = @import("raylib");
 const sandbox = @import("sandbox.zig");
 const comp_source = @embedFile("shaders/entity_update.comp");
 // GL constants not exposed by raylib-zig
 const GL_SHADER_STORAGE_BARRIER_BIT: u32 = 0x00002000;
 // function pointer type for glMemoryBarrier
 const GlMemoryBarrierFn = *const fn (barriers: u32) callconv(.c) void;
 pub const ComputeShader = struct {
    program_id: u32,
    entity_count_loc: i32,
    frame_number_loc: i32,
    screen_size_loc: i32,
    center_loc: i32,
    respawn_radius_loc: i32,
    entity_speed_loc: i32,
    glMemoryBarrier: GlMemoryBarrierFn,
    pub fn init() ?ComputeShader {
        // load glMemoryBarrier dynamically
        const barrier_ptr = rl.gl.rlGetProcAddress("glMemoryBarrier");
        const glMemoryBarrier: GlMemoryBarrierFn = @ptrCast(@alignCast(barrier_ptr));
        // compile compute shader
        const shader_id = rl.gl.rlCompileShader(comp_source, rl.gl.rl_compute_shader);
        if (shader_id == 0) {
            std.debug.print("compute: failed to compile compute shader\n", .{});
            return null;
        }
        // link compute program
        const program_id = rl.gl.rlLoadComputeShaderProgram(shader_id);
        if (program_id == 0) {
            std.debug.print("compute: failed to link compute program\n", .{});
            return null;
        }
        // get uniform locations
        const entity_count_loc = rl.gl.rlGetLocationUniform(program_id, "entityCount");
        const frame_number_loc = rl.gl.rlGetLocationUniform(program_id, "frameNumber");
        const screen_size_loc = rl.gl.rlGetLocationUniform(program_id, "screenSize");
        const center_loc = rl.gl.rlGetLocationUniform(program_id, "center");
        const respawn_radius_loc = rl.gl.rlGetLocationUniform(program_id, "respawnRadius");
        const entity_speed_loc = rl.gl.rlGetLocationUniform(program_id, "entitySpeed");
        std.debug.print("compute: shader loaded\n", .{});
        return .{
            .program_id = program_id,
            .entity_count_loc = entity_count_loc,
            .frame_number_loc = frame_number_loc,
            .screen_size_loc = screen_size_loc,
            .center_loc = center_loc,
            .respawn_radius_loc = respawn_radius_loc,
            .entity_speed_loc = entity_speed_loc,
            .glMemoryBarrier = glMemoryBarrier,
        };
    }
    pub fn deinit(self: *ComputeShader) void {
        rl.gl.rlUnloadShaderProgram(self.program_id);
    }
    pub fn dispatch(self: *ComputeShader, ssbo_id: u32, entity_count: u32, frame_number: u32) void {
        if (entity_count == 0) return;
        // constants from sandbox.zig
        const screen_w: f32 = @floatFromInt(sandbox.SCREEN_WIDTH);
        const screen_h: f32 = @floatFromInt(sandbox.SCREEN_HEIGHT);
        const center_x: f32 = screen_w / 2.0;
        const center_y: f32 = screen_h / 2.0;
        const respawn_radius: f32 = 10.0; // RESPAWN_THRESHOLD
        const entity_speed: f32 = 2.0; // ENTITY_SPEED
        // bind compute shader
        rl.gl.rlEnableShader(self.program_id);
        // set uniforms
        rl.gl.rlSetUniform(self.entity_count_loc, &entity_count, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_uint), 1);
        rl.gl.rlSetUniform(self.frame_number_loc, &frame_number, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_uint), 1);
        const screen_size = [2]f32{ screen_w, screen_h };
        rl.gl.rlSetUniform(self.screen_size_loc, &screen_size, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_vec2), 1);
        const center = [2]f32{ center_x, center_y };
        rl.gl.rlSetUniform(self.center_loc, &center, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_vec2), 1);
        rl.gl.rlSetUniform(self.respawn_radius_loc, &respawn_radius, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_float), 1);
        rl.gl.rlSetUniform(self.entity_speed_loc, &entity_speed, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_float), 1);
        // bind SSBO to binding point 0
        rl.gl.rlBindShaderBuffer(ssbo_id, 0);
        // dispatch compute workgroups: ceil(entity_count / 256)
        const groups = (entity_count + 255) / 256;
        rl.gl.rlComputeShaderDispatch(groups, 1, 1);
        // memory barrier - ensure compute writes are visible to vertex shader
        self.glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
        // unbind
        rl.gl.rlBindShaderBuffer(0, 0);
    }
 };
--- a/src/sandbox.zig
+++ b/src/sandbox.zig
@ -287,69 +287,34 @@ test "update respawns entity at edge when reaching center" {
    try std.testing.expect(on_left or on_right or on_top or on_bottom);
 }
-// GPU entity for SSBO rendering (16 bytes, matches compute shader layout)
+// GPU entity for SSBO rendering (position + color only, no velocity)
 pub const GpuEntity = extern struct {
    x: f32,
    y: f32,
    packed_vel: i32, // vx high 16 bits, vy low 16 bits (fixed-point 8.8)
    color: u32,
 };
 // pack two f32 velocities into a single i32 (fixed-point 8.8 format)
 pub fn packVelocity(vx: f32, vy: f32) i32 {
    const vx_fixed: i16 = @intFromFloat(std.math.clamp(vx * 256.0, -32768.0, 32767.0));
    const vy_fixed: i16 = @intFromFloat(std.math.clamp(vy * 256.0, -32768.0, 32767.0));
    return (@as(i32, vx_fixed) << 16) | (@as(i32, vy_fixed) & 0xFFFF);
 }
 test "GpuEntity struct has correct size for SSBO" {
-    // SSBO layout: x(4) + y(4) + packed_vel(4) + color(4) = 16 bytes
+    // SSBO layout: x(4) + y(4) + color(4) = 12 bytes
-    try std.testing.expectEqual(@as(usize, 16), @sizeOf(GpuEntity));
+    try std.testing.expectEqual(@as(usize, 12), @sizeOf(GpuEntity));
 }
 test "GpuEntity can be created from Entity" {
    const entity = Entity{
        .x = 100.0,
        .y = 200.0,
-        .vx = 1.5,
+        .vx = 1.5, // ignored for GPU
-        .vy = -0.5,
+        .vy = -0.5, // ignored for GPU
        .color = 0x00FFFF,
    };
    const gpu_entity = GpuEntity{
        .x = entity.x,
        .y = entity.y,
        .packed_vel = packVelocity(entity.vx, entity.vy),
        .color = entity.color,
    };
    try std.testing.expectEqual(@as(f32, 100.0), gpu_entity.x);
    try std.testing.expectEqual(@as(f32, 200.0), gpu_entity.y);
    try std.testing.expectEqual(@as(u32, 0x00FFFF), gpu_entity.color);
    // unpack and verify velocity (should round-trip within precision)
    const vx_unpacked = @as(f32, @floatFromInt(@as(i16, @truncate(gpu_entity.packed_vel >> 16)))) / 256.0;
    const vy_unpacked = @as(f32, @floatFromInt(@as(i16, @truncate(gpu_entity.packed_vel)))) / 256.0;
    try std.testing.expectApproxEqAbs(@as(f32, 1.5), vx_unpacked, 0.004);
    try std.testing.expectApproxEqAbs(@as(f32, -0.5), vy_unpacked, 0.004);
 }
 test "packVelocity round-trips correctly" {
    // test positive values
    const packed1 = packVelocity(2.0, 1.5);
    const vx1 = @as(f32, @floatFromInt(@as(i16, @truncate(packed1 >> 16)))) / 256.0;
    const vy1 = @as(f32, @floatFromInt(@as(i16, @truncate(packed1)))) / 256.0;
    try std.testing.expectApproxEqAbs(@as(f32, 2.0), vx1, 0.004);
    try std.testing.expectApproxEqAbs(@as(f32, 1.5), vy1, 0.004);
    // test negative values
    const packed2 = packVelocity(-1.0, -2.5);
    const vx2 = @as(f32, @floatFromInt(@as(i16, @truncate(packed2 >> 16)))) / 256.0;
    const vy2 = @as(f32, @floatFromInt(@as(i16, @truncate(packed2)))) / 256.0;
    try std.testing.expectApproxEqAbs(@as(f32, -1.0), vx2, 0.004);
    try std.testing.expectApproxEqAbs(@as(f32, -2.5), vy2, 0.004);
    // test zero
    const packed3 = packVelocity(0.0, 0.0);
    try std.testing.expectEqual(@as(i32, 0), packed3);
 }
--- a/src/sandbox_main.zig
+++ b/src/sandbox_main.zig
@ -3,11 +3,9 @@
 const std = @import("std");
 const rl = @import("raylib");
 const ztracy = @import("ztracy");
 const sandbox = @import("sandbox.zig");
 const ui = @import("ui.zig");
 const SsboRenderer = @import("ssbo_renderer.zig").SsboRenderer;
 const ComputeShader = @import("compute.zig").ComputeShader;
 const SCREEN_WIDTH = sandbox.SCREEN_WIDTH;
 const SCREEN_HEIGHT = sandbox.SCREEN_HEIGHT;
@ -33,11 +31,6 @@ const BENCH_RAMP_AMOUNT: usize = 50_000; // entities added per ramp
 const BENCH_EXIT_THRESHOLD_MS: f32 = 25.0; // exit when frame time exceeds this
 const BENCH_EXIT_SUSTAIN: f32 = 1.0; // must stay above threshold for this long
 // zoom settings
 const ZOOM_MIN: f32 = 1.0;
 const ZOOM_MAX: f32 = 10.0;
 const ZOOM_SPEED: f32 = 0.1; // multiplier per scroll tick
 const BenchmarkLogger = struct {
    file: ?std.fs.File,
    last_logged_frame_ms: f32,
@ -164,7 +157,6 @@ pub fn main() !void {
    var use_instancing = false;
    var use_ssbo = true;
    var use_vsync = false;
    var use_compute = true; // GPU compute is now default
    var args = try std.process.argsWithAllocator(std.heap.page_allocator);
    defer args.deinit();
    _ = args.skip(); // skip program name
@ -178,8 +170,6 @@ pub fn main() !void {
            use_ssbo = false; // legacy rlgl batched path
        } else if (std.mem.eql(u8, arg, "--vsync")) {
            use_vsync = true;
        } else if (std.mem.eql(u8, arg, "--cpu")) {
            use_compute = false; // fallback to CPU update path
        }
    }
@ -189,11 +179,6 @@ pub fn main() !void {
    rl.initWindow(@intCast(SCREEN_WIDTH), @intCast(SCREEN_HEIGHT), "lofivor sandbox");
    defer rl.closeWindow();
    // show background immediately (avoid black screen during init)
    rl.beginDrawing();
    rl.clearBackground(BG_COLOR);
    rl.endDrawing();
    // use larger batch buffer: 16384 elements vs default 8192
    // fewer flushes = less driver overhead per frame
    const numElements: i32 = 8192 * 4; // quads = 4 verts
@ -261,26 +246,6 @@ pub fn main() !void {
        if (ssbo_renderer) |*r| r.deinit();
    }
    // compute shader setup (only if --compute flag)
    var compute_shader: ?ComputeShader = null;
    if (use_compute) {
        if (!use_ssbo) {
            std.debug.print("--compute requires SSBO mode (default), ignoring\n", .{});
        } else {
            compute_shader = ComputeShader.init();
            if (compute_shader == null) {
                std.debug.print("failed to initialize compute shader, falling back to CPU\n", .{});
            } else {
                std.debug.print("compute shader mode enabled\n", .{});
            }
        }
    }
    defer {
        if (compute_shader) |*c| c.deinit();
    }
    // load UI font (embedded)
    const font_data = @embedFile("verdanab.ttf");
    const ui_font = rl.loadFontFromMemory(".ttf", font_data, 32, null) catch {
@ -294,11 +259,6 @@ pub fn main() !void {
    var rng = prng.random();
    var paused = false;
    // camera state for zoom/pan
    var zoom: f32 = 1.0;
    var pan = @Vector(2, f32){ 0, 0 };
    var logger = BenchmarkLogger.init();
    defer logger.deinit();
@ -306,7 +266,6 @@ pub fn main() !void {
    var update_time_us: i64 = 0;
    var render_time_us: i64 = 0;
    var elapsed: f32 = 0;
    var frame_number: u32 = 0;
    // auto-benchmark state
    var last_ramp_time: f32 = 0;
@ -352,47 +311,24 @@ pub fn main() !void {
        } else {
            // manual controls
            handleInput(&entities, &rng, &paused);
            if (handleCamera(&zoom, &pan)) break;
        }
        // update
        if (!paused) {
            const tracy_update = ztracy.ZoneN(@src(), "update");
            defer tracy_update.End();
            const update_start = std.time.microTimestamp();
-
+            sandbox.update(&entities, &rng);
            if (compute_shader == null) {
                // CPU update path (positions + respawn)
                sandbox.update(&entities, &rng);
            }
            // GPU compute path handles update in render section before draw
            update_time_us = std.time.microTimestamp() - update_start;
        }
        // render
        const tracy_render = ztracy.ZoneN(@src(), "render");
        defer tracy_render.End();
        const render_start = std.time.microTimestamp();
        rl.beginDrawing();
        rl.clearBackground(BG_COLOR);
        if (use_ssbo) {
-            // dispatch compute shader before render (if enabled)
+            // SSBO instanced rendering path (12 bytes per entity)
-            if (compute_shader) |*cs| {
+            ssbo_renderer.?.render(&entities);
                if (!paused) {
                    const tracy_compute = ztracy.ZoneN(@src(), "compute_dispatch");
                    defer tracy_compute.End();
                    cs.dispatch(ssbo_renderer.?.ssbo_id, @intCast(entities.count), frame_number);
                    frame_number +%= 1;
                }
                // GPU compute mode - only upload new entities, positions updated on GPU
                ssbo_renderer.?.renderComputeMode(&entities, zoom, pan);
            } else {
                // CPU mode - upload entity data to GPU
                ssbo_renderer.?.render(&entities, zoom, pan);
            }
        } else if (use_instancing) {
            // GPU instancing path (64 bytes per entity)
            const xforms = transforms.?;
@ -443,8 +379,7 @@ pub fn main() !void {
        // metrics overlay (skip in bench mode for cleaner headless run)
        if (!bench_mode) {
-            ui.drawMetrics(&entities, update_time_us, render_time_us, paused, zoom, ui_font);
+            ui.drawMetrics(&entities, update_time_us, render_time_us, paused, ui_font);
            ui.drawMemory(entities.count, ui_font);
        }
        rl.endDrawing();
@ -455,9 +390,6 @@ pub fn main() !void {
        const update_ms = @as(f32, @floatFromInt(update_time_us)) / 1000.0;
        const render_ms = @as(f32, @floatFromInt(render_time_us)) / 1000.0;
        logger.log(elapsed, entities.count, frame_ms, update_ms, render_ms);
        // tracy frame mark
        ztracy.FrameMark();
    }
 }
@ -512,86 +444,4 @@ fn handleInput(entities: *sandbox.Entities, rng: *std.Random, paused: *bool) voi
    if (rl.isKeyPressed(.space)) {
        paused.* = !paused.*;
    }
    // toggle ui: tab
    if (rl.isKeyPressed(.tab)) {
        ui.show_ui = !ui.show_ui;
    }
 }
 fn handleCamera(zoom: *f32, pan: *@Vector(2, f32)) bool {
    const wheel = rl.getMouseWheelMove();
    if (wheel != 0) {
        const mouse_pos = rl.getMousePosition();
        const old_zoom = zoom.*;
        // calculate new zoom
        const zoom_factor = if (wheel > 0) (1.0 + ZOOM_SPEED) else (1.0 / (1.0 + ZOOM_SPEED));
        var new_zoom = old_zoom * zoom_factor;
        new_zoom = std.math.clamp(new_zoom, ZOOM_MIN, ZOOM_MAX);
        if (new_zoom != old_zoom) {
            // zoom toward mouse cursor:
            // keep the world point under the cursor stationary
            // world_pos = (screen_pos / old_zoom) + old_pan
            // new_pan = world_pos - (screen_pos / new_zoom)
            const world_x = (mouse_pos.x / old_zoom) + pan.*[0];
            const world_y = (mouse_pos.y / old_zoom) + pan.*[1];
            pan.*[0] = world_x - (mouse_pos.x / new_zoom);
            pan.*[1] = world_y - (mouse_pos.y / new_zoom);
            zoom.* = new_zoom;
            // clamp pan to bounds
            clampPan(pan, zoom.*);
        }
    }
    // pan with any mouse button drag (only when zoomed in)
    if (zoom.* > 1.0) {
        const any_button = rl.isMouseButtonDown(.left) or
            rl.isMouseButtonDown(.right) or
            rl.isMouseButtonDown(.middle);
        if (any_button) {
            const delta = rl.getMouseDelta();
            // drag down = view down, drag right = view right
            pan.*[0] -= delta.x / zoom.*;
            pan.*[1] += delta.y / zoom.*;
            clampPan(pan, zoom.*);
        }
    }
    // reset on Return or Enter
    if (rl.isKeyPressed(.enter) or rl.isKeyPressed(.kp_enter)) {
        zoom.* = 1.0;
        pan.* = @Vector(2, f32){ 0, 0 };
    }
    // q: reset zoom if zoomed in, otherwise quit
    if (rl.isKeyPressed(.q)) {
        if (zoom.* > 1.0) {
            zoom.* = 1.0;
            pan.* = @Vector(2, f32){ 0, 0 };
        } else {
            return true; // signal to quit
        }
    }
    return false;
 }
 fn clampPan(pan: *@Vector(2, f32), zoom: f32) void {
    // when zoomed in, limit pan so viewport stays in simulation bounds
    // visible area = screen_size / zoom
    // max pan = world_size - visible_area
    const screen_w: f32 = @floatFromInt(SCREEN_WIDTH);
    const screen_h: f32 = @floatFromInt(SCREEN_HEIGHT);
    const visible_w = screen_w / zoom;
    const visible_h = screen_h / zoom;
    const max_pan_x = @max(0, screen_w - visible_w);
    const max_pan_y = @max(0, screen_h - visible_h);
    pan.*[0] = std.math.clamp(pan.*[0], 0, max_pan_x);
    pan.*[1] = std.math.clamp(pan.*[1], 0, max_pan_y);
 }
--- a/src/shaders/entity.vert
+++ b/src/shaders/entity.vert
@ -4,11 +4,10 @@
 layout(location = 0) in vec2 position;
 layout(location = 1) in vec2 texCoord;
-// entity data from SSBO (16 bytes, matches compute shader layout)
+// entity data from SSBO
 struct Entity {
    float x;
    float y;
    int packedVel;  // vx high 16 bits, vy low 16 bits (fixed-point 8.8), unused in vertex shader
    uint color;
 };
@ -18,8 +17,6 @@ layout(std430, binding = 0) readonly buffer EntityData {
 // screen size for NDC conversion
 uniform vec2 screenSize;
 uniform float zoom;
 uniform vec2 pan;
 out vec2 fragTexCoord;
 out vec3 fragColor;
@ -28,13 +25,13 @@ void main() {
    // get entity data from SSBO
    Entity e = entities[gl_InstanceID];
-    // apply pan offset and zoom to convert to NDC
+    // convert entity position to NDC
-    // pan is in screen pixels, zoom scales the view
+    // entity coords are in screen pixels, convert to [-1, 1]
-    float ndcX = ((e.x - pan.x) * zoom / screenSize.x) * 2.0 - 1.0;
+    float ndcX = (e.x / screenSize.x) * 2.0 - 1.0;
-    float ndcY = ((e.y - pan.y) * zoom / screenSize.y) * 2.0 - 1.0;
+    float ndcY = (e.y / screenSize.y) * 2.0 - 1.0;
-    // quad size in NDC (16 pixels, scaled by zoom)
+    // quad size in NDC (16 pixels)
-    float quadSizeNdc = (16.0 * zoom) / screenSize.x;
+    float quadSizeNdc = 16.0 / screenSize.x;
    // offset by quad corner position
    gl_Position = vec4(ndcX + position.x * quadSizeNdc,
--- a/src/shaders/entity_update.comp
+++ b/src/shaders/entity_update.comp
@ -1,97 +0,0 @@
 #version 430
 layout(local_size_x = 256) in;
 struct Entity {
    float x;
    float y;
    int packedVel;  // vx high 16 bits, vy low 16 bits (fixed-point 8.8)
    uint color;
 };
 layout(std430, binding = 0) buffer Entities {
    Entity entities[];
 };
 uniform uint entityCount;
 uniform uint frameNumber;
 uniform vec2 screenSize;
 uniform vec2 center;
 uniform float respawnRadius;
 uniform float entitySpeed;
 // PCG-style GPU RNG - returns value in [0, 1)
 uint pcg(inout uint state) {
    state = state * 747796405u + 2891336453u;
    uint word = ((state >> ((state >> 28u) + 4u)) ^ state) * 277803737u;
    return (word >> 22u) ^ word;
 }
 float randFloat(inout uint state) {
    return float(pcg(state)) / 4294967296.0;
 }
 // pack velocity into fixed-point 8.8 format
 int packVelocity(float vx, float vy) {
    int vx_fixed = int(clamp(vx * 256.0, -32768.0, 32767.0));
    int vy_fixed = int(clamp(vy * 256.0, -32768.0, 32767.0));
    return (vx_fixed << 16) | (vy_fixed & 0xFFFF);
 }
 void main() {
    uint id = gl_GlobalInvocationID.x;
    if (id >= entityCount) return;
    Entity e = entities[id];
    // unpack velocity (fixed-point 8.8)
    float vx = float(e.packedVel >> 16) / 256.0;
    float vy = float((e.packedVel << 16) >> 16) / 256.0;  // sign-extend low 16 bits
    // update position
    e.x += vx;
    e.y += vy;
    // check if reached center - respawn at edge
    float dx = e.x - center.x;
    float dy = e.y - center.y;
    if (dx*dx + dy*dy < respawnRadius * respawnRadius) {
        // init RNG with entity id and frame number
        uint rng = id * 1103515245u + frameNumber * 12345u + 1u;
        // pick random edge: 0=top, 1=bottom, 2=left, 3=right
        uint edge = pcg(rng) & 3u;
        float t = randFloat(rng);
        // spawn on edge
        if (edge == 0u) {  // top
            e.x = t * screenSize.x;
            e.y = 0.0;
        } else if (edge == 1u) {  // bottom
            e.x = t * screenSize.x;
            e.y = screenSize.y;
        } else if (edge == 2u) {  // left
            e.x = 0.0;
            e.y = t * screenSize.y;
        } else {  // right
            e.x = screenSize.x;
            e.y = t * screenSize.y;
        }
        // velocity toward center
        dx = center.x - e.x;
        dy = center.y - e.y;
        float dist = sqrt(dx*dx + dy*dy);
        vx = (dx / dist) * entitySpeed;
        vy = (dy / dist) * entitySpeed;
        e.packedVel = packVelocity(vx, vy);
        // new random color
        uint r = pcg(rng) & 0xFFu;
        uint g = pcg(rng) & 0xFFu;
        uint b = pcg(rng) & 0xFFu;
        e.color = (r << 16u) | (g << 8u) | b;
    }
    entities[id] = e;
 }
--- a/src/ssbo_renderer.zig
+++ b/src/ssbo_renderer.zig
@ -3,7 +3,6 @@
 const std = @import("std");
 const rl = @import("raylib");
 const ztracy = @import("ztracy");
 const sandbox = @import("sandbox.zig");
 const SCREEN_WIDTH = sandbox.SCREEN_WIDTH;
@ -20,11 +19,8 @@ pub const SsboRenderer = struct {
    ssbo_id: u32,
    screen_size_loc: i32,
    circle_texture_loc: i32,
    zoom_loc: i32,
    pan_loc: i32,
    circle_texture_id: u32,
    gpu_buffer: []sandbox.GpuEntity,
    last_entity_count: usize, // track count to detect when entities are added
    const QUAD_SIZE: f32 = 16.0;
@ -57,8 +53,6 @@ pub const SsboRenderer = struct {
        // get uniform locations
        const screen_size_loc = rl.gl.rlGetLocationUniform(shader_id, "screenSize");
        const circle_texture_loc = rl.gl.rlGetLocationUniform(shader_id, "circleTexture");
        const zoom_loc = rl.gl.rlGetLocationUniform(shader_id, "zoom");
        const pan_loc = rl.gl.rlGetLocationUniform(shader_id, "pan");
        if (screen_size_loc < 0) {
            std.debug.print("ssbo: warning - screenSize uniform not found\n", .{});
@ -100,7 +94,7 @@ pub const SsboRenderer = struct {
        rl.gl.rlSetVertexAttribute(1, 2, rl.gl.rl_float, false, 4 * @sizeOf(f32), 2 * @sizeOf(f32));
        rl.gl.rlEnableVertexAttribute(1);
-        // create SSBO for entity data (16 bytes per entity, 1M entities = 16MB)
+        // create SSBO for entity data (12 bytes per entity, 1M entities = 12MB)
        const ssbo_size: u32 = @intCast(sandbox.MAX_ENTITIES * @sizeOf(sandbox.GpuEntity));
        const ssbo_id = rl.gl.rlLoadShaderBuffer(ssbo_size, null, rl.gl.rl_dynamic_draw);
        if (ssbo_id == 0) {
@ -122,11 +116,8 @@ pub const SsboRenderer = struct {
            .ssbo_id = ssbo_id,
            .screen_size_loc = screen_size_loc,
            .circle_texture_loc = circle_texture_loc,
            .zoom_loc = zoom_loc,
            .pan_loc = pan_loc,
            .circle_texture_id = circle_texture.id,
            .gpu_buffer = gpu_buffer,
            .last_entity_count = 0,
        };
    }
@ -138,80 +129,25 @@ pub const SsboRenderer = struct {
        std.heap.page_allocator.free(self.gpu_buffer);
    }
-    pub fn render(self: *SsboRenderer, entities: *const sandbox.Entities, zoom: f32, pan: @Vector(2, f32)) void {
+    pub fn render(self: *SsboRenderer, entities: *const sandbox.Entities) void {
        self.renderInternal(entities, zoom, pan, false);
    }
    pub fn renderComputeMode(self: *SsboRenderer, entities: *const sandbox.Entities, zoom: f32, pan: @Vector(2, f32)) void {
        if (entities.count == 0) return;
        // flush raylib's internal render batch before our custom GL calls
        rl.gl.rlDrawRenderBatchActive();
-        // upload NEW entities when count increases (entities added on CPU)
+        // copy entity data to GPU buffer (position + color only)
-        if (entities.count > self.last_entity_count) {
+        for (entities.items[0..entities.count], 0..) |entity, i| {
-            const zone = ztracy.ZoneN(@src(), "ssbo_upload_new");
+            self.gpu_buffer[i] = .{
-            defer zone.End();
+                .x = entity.x,
-
+                .y = entity.y,
-            // copy new entities to GPU buffer
+                .color = entity.color,
-            for (entities.items[self.last_entity_count..entities.count], self.last_entity_count..) |entity, i| {
+            };
                self.gpu_buffer[i] = .{
                    .x = entity.x,
                    .y = entity.y,
                    .packed_vel = sandbox.packVelocity(entity.vx, entity.vy),
                    .color = entity.color,
                };
            }
            // upload only the new portion to SSBO
            const offset: u32 = @intCast(self.last_entity_count * @sizeOf(sandbox.GpuEntity));
            const new_count = entities.count - self.last_entity_count;
            const data_size: u32 = @intCast(new_count * @sizeOf(sandbox.GpuEntity));
            rl.gl.rlUpdateShaderBuffer(self.ssbo_id, &self.gpu_buffer[self.last_entity_count], data_size, offset);
            self.last_entity_count = entities.count;
        } else if (entities.count < self.last_entity_count) {
            // entities were removed, update count
            self.last_entity_count = entities.count;
        }
-        self.drawInstanced(entities.count, zoom, pan);
+        // upload to SSBO
-    }
+        const data_size: u32 = @intCast(entities.count * @sizeOf(sandbox.GpuEntity));
        rl.gl.rlUpdateShaderBuffer(self.ssbo_id, self.gpu_buffer.ptr, data_size, 0);
    fn renderInternal(self: *SsboRenderer, entities: *const sandbox.Entities, zoom: f32, pan: @Vector(2, f32), skip_upload: bool) void {
        if (entities.count == 0) return;
        // flush raylib's internal render batch before our custom GL calls
        rl.gl.rlDrawRenderBatchActive();
        if (!skip_upload) {
            // copy entity data to GPU buffer (position + packed velocity + color)
            {
                const zone = ztracy.ZoneN(@src(), "ssbo_copy");
                defer zone.End();
                for (entities.items[0..entities.count], 0..) |entity, i| {
                    self.gpu_buffer[i] = .{
                        .x = entity.x,
                        .y = entity.y,
                        .packed_vel = sandbox.packVelocity(entity.vx, entity.vy),
                        .color = entity.color,
                    };
                }
            }
            // upload to SSBO
            {
                const zone = ztracy.ZoneN(@src(), "ssbo_upload");
                defer zone.End();
                const data_size: u32 = @intCast(entities.count * @sizeOf(sandbox.GpuEntity));
                rl.gl.rlUpdateShaderBuffer(self.ssbo_id, self.gpu_buffer.ptr, data_size, 0);
            }
        }
        self.drawInstanced(entities.count, zoom, pan);
    }
    fn drawInstanced(self: *SsboRenderer, entity_count: usize, zoom: f32, pan: @Vector(2, f32)) void {
        // bind shader
        rl.gl.rlEnableShader(self.shader_id);
@ -219,13 +155,6 @@ pub const SsboRenderer = struct {
        const screen_size = [2]f32{ @floatFromInt(SCREEN_WIDTH), @floatFromInt(SCREEN_HEIGHT) };
        rl.gl.rlSetUniform(self.screen_size_loc, &screen_size, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_vec2), 1);
        // set zoom uniform
        rl.gl.rlSetUniform(self.zoom_loc, &zoom, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_float), 1);
        // set pan uniform
        const pan_arr = [2]f32{ pan[0], pan[1] };
        rl.gl.rlSetUniform(self.pan_loc, &pan_arr, @intFromEnum(rl.gl.rlShaderUniformDataType.rl_shader_uniform_vec2), 1);
        // bind texture
        rl.gl.rlActiveTextureSlot(0);
        rl.gl.rlEnableTexture(self.circle_texture_id);
@ -241,13 +170,9 @@ pub const SsboRenderer = struct {
        rl.gl.rlSetBlendMode(@intFromEnum(rl.gl.rlBlendMode.rl_blend_alpha));
        // bind VAO and draw
-        {
+        _ = rl.gl.rlEnableVertexArray(self.vao_id);
-            const zone = ztracy.ZoneN(@src(), "ssbo_draw");
+        rl.gl.rlEnableVertexBuffer(self.vbo_id);
-            defer zone.End();
+        rl.gl.rlDrawVertexArrayInstanced(0, 6, @intCast(entities.count));
            _ = rl.gl.rlEnableVertexArray(self.vao_id);
            rl.gl.rlEnableVertexBuffer(self.vbo_id);
            rl.gl.rlDrawVertexArrayInstanced(0, 6, @intCast(entity_count));
        }
        // cleanup - restore raylib's expected state
        rl.gl.rlDisableVertexArray();
--- a/src/ui.zig
+++ b/src/ui.zig
@ -19,23 +19,13 @@ pub const box_padding: f32 = 8;
 pub const text_color = rl.Color.white;
 pub const dim_text_color = rl.Color.gray;
 pub const highlight_color = rl.Color.yellow;
 pub const fps_good_color = rl.Color.green;
 pub const fps_bad_color = rl.Color.red;
 pub const box_bg = rl.Color{ .r = 0, .g = 0, .b = 0, .a = 200 };
 // =============================================================================
 // state
 // =============================================================================
 pub var show_ui: bool = true;
 // =============================================================================
 // drawing functions
 // =============================================================================
-pub fn drawMetrics(entities: *const sandbox.Entities, update_us: i64, render_us: i64, paused: bool, zoom: f32, font: rl.Font) void {
+pub fn drawMetrics(entities: *const sandbox.Entities, update_us: i64, render_us: i64, paused: bool, font: rl.Font) void {
    if (!show_ui) return;
    var buf: [256]u8 = undefined;
    // fps box (above metrics)
@ -43,16 +33,13 @@ pub fn drawMetrics(entities: *const sandbox.Entities, update_us: i64, render_us:
    rl.drawRectangle(5, 5, 180, fps_box_height, box_bg);
    const frame_ms = rl.getFrameTime() * 1000.0;
    const fps = if (frame_ms > 0) 1000.0 / frame_ms else 0;
-    rl.drawTextEx(font, "FPS: ", .{ .x = padding, .y = padding }, font_size, 0, text_color);
+    const fps_text = std.fmt.bufPrintZ(&buf, "FPS: {d:.0}", .{fps}) catch "?";
-    const fps_text = std.fmt.bufPrintZ(&buf, "{d:.0}", .{fps}) catch "?";
+    rl.drawTextEx(font, fps_text, .{ .x = padding, .y = padding }, font_size, 0, text_color);
    const fps_color = if (fps >= 60.0) fps_good_color else fps_bad_color;
    const label_width = rl.measureTextEx(font, "FPS: ", font_size, 0).x;
    rl.drawTextEx(font, fps_text, .{ .x = padding + label_width, .y = padding }, font_size, 0, fps_color);
    // metrics box (below fps)
    const metrics_y: i32 = 5 + fps_box_height + 5;
    var y: f32 = @as(f32, @floatFromInt(metrics_y)) + box_padding;
-    const bg_height: i32 = if (paused) 150 else 120;
+    const bg_height: i32 = if (paused) 130 else 100;
    rl.drawRectangle(5, metrics_y, 180, bg_height, box_bg);
    // entity count
@ -77,11 +64,6 @@ pub fn drawMetrics(entities: *const sandbox.Entities, update_us: i64, render_us:
    rl.drawTextEx(font, render_text, .{ .x = padding, .y = y }, font_size, 0, text_color);
    y += line_height;
    // zoom level
    const zoom_text = std.fmt.bufPrintZ(&buf, "zoom:     {d:.1}x", .{zoom}) catch "?";
    rl.drawTextEx(font, zoom_text, .{ .x = padding, .y = y }, font_size, 0, if (zoom > 1.0) highlight_color else text_color);
    y += line_height;
    // paused indicator
    if (paused) {
        y += line_height;
@ -92,43 +74,8 @@ pub fn drawMetrics(entities: *const sandbox.Entities, update_us: i64, render_us:
    drawControls(font, metrics_y + bg_height);
 }
 pub fn drawMemory(entity_count: usize, font: rl.Font) void {
    if (!show_ui) return;
    var buf: [256]u8 = undefined;
    const box_width: i32 = 160;
    const box_height: i32 = @intFromFloat(line_height * 3 + box_padding * 2);
    const box_x: i32 = @as(i32, @intCast(sandbox.SCREEN_WIDTH)) - box_width - 5;
    const box_y: i32 = 5;
    rl.drawRectangle(box_x, box_y, box_width, box_height, box_bg);
    var y: f32 = @as(f32, @floatFromInt(box_y)) + box_padding;
    const x: f32 = @floatFromInt(box_x + @as(i32, @intFromFloat(box_padding)));
    // entity memory (CPU side)
    const entity_bytes = entity_count * @sizeOf(sandbox.Entity);
    const entity_mb = @as(f32, @floatFromInt(entity_bytes)) / (1024.0 * 1024.0);
    const entity_text = std.fmt.bufPrintZ(&buf, "cpu:  {d:.1} MB", .{entity_mb}) catch "?";
    rl.drawTextEx(font, entity_text, .{ .x = x, .y = y }, font_size, 0, text_color);
    y += line_height;
    // GPU buffer memory (SSBO)
    const gpu_bytes = entity_count * @sizeOf(sandbox.GpuEntity);
    const gpu_mb = @as(f32, @floatFromInt(gpu_bytes)) / (1024.0 * 1024.0);
    const gpu_text = std.fmt.bufPrintZ(&buf, "gpu:  {d:.1} MB", .{gpu_mb}) catch "?";
    rl.drawTextEx(font, gpu_text, .{ .x = x, .y = y }, font_size, 0, text_color);
    y += line_height;
    // total
    const total_mb = entity_mb + gpu_mb;
    const total_text = std.fmt.bufPrintZ(&buf, "total: {d:.1} MB", .{total_mb}) catch "?";
    rl.drawTextEx(font, total_text, .{ .x = x, .y = y }, font_size, 0, dim_text_color);
 }
 fn drawControls(font: rl.Font, metrics_bottom: i32) void {
-    const ctrl_box_height: i32 = @intFromFloat(small_line_height * 7 + box_padding * 2);
+    const ctrl_box_height: i32 = @intFromFloat(small_line_height * 4 + box_padding * 2);
    const ctrl_box_y: i32 = metrics_bottom + 5;
    rl.drawRectangle(5, ctrl_box_y, 175, ctrl_box_height, box_bg);
@ -137,11 +84,8 @@ fn drawControls(font: rl.Font, metrics_bottom: i32) void {
    const controls = [_][]const u8{
        "+/-: 10k entities",
        "shift +/-: 50k",
-        "scroll: zoom",
+        "space: pause",
-        "drag: pan (zoomed)",
+        "r: reset",
        "space: pause, r: reset",
        "q: zoom out / quit",
        "tab: toggle ui",
    };
    for (controls) |text| {