diff --git a/.gitignore b/.gitignore
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--- a/.gitignore
+++ b/.gitignore
@@ -0,0 +1 @@
+.ipynb_checkpoints/
diff --git a/notebook.ipynb b/notebook.ipynb
new file mode 100644
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--- /dev/null
+++ b/notebook.ipynb
@@ -0,0 +1,193 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# perspective projection\n",
+    "\n",
+    "```\n",
+    "x' = x / z\n",
+    "y' = y / z\n",
+    "```\n",
+    "\n",
+    "divide by distance. that's it."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# a cube: 8 vertices, 12 edges\n",
+    "\n",
+    "vertices = [\n",
+    "    (-1, -1, -1),\n",
+    "    ( 1, -1, -1),\n",
+    "    ( 1,  1, -1),\n",
+    "    (-1,  1, -1),\n",
+    "    (-1, -1,  1),\n",
+    "    ( 1, -1,  1),\n",
+    "    ( 1,  1,  1),\n",
+    "    (-1,  1,  1),\n",
+    "]\n",
+    "\n",
+    "edges = [\n",
+    "    (0, 1), (1, 2), (2, 3), (3, 0),  # front\n",
+    "    (4, 5), (5, 6), (6, 7), (7, 4),  # back\n",
+    "    (0, 4), (1, 5), (2, 6), (3, 7),  # connecting\n",
+    "]\n",
+    "\n",
+    "print(f\"{len(vertices)} vertices, {len(edges)} edges\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# the formula\n",
+    "\n",
+    "def project(x, y, z):\n",
+    "    return (x / z, y / z)\n",
+    "\n",
+    "# example: a point at (2, 1, 4)\n",
+    "x, y, z = 2, 1, 4\n",
+    "x_proj, y_proj = project(x, y, z)\n",
+    "\n",
+    "print(f\"3d point: ({x}, {y}, {z})\")\n",
+    "print(f\"2d projection: ({x_proj}, {y_proj})\")\n",
+    "print(f\"\\nfarther away = smaller on screen\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# static cube\n",
+    "\n",
+    "from IPython.display import HTML\n",
+    "\n",
+    "HTML(\"\"\"\n",
+    "<canvas id=\"static\" width=\"300\" height=\"300\" style=\"background:#111\"></canvas>\n",
+    "<script>\n",
+    "(function() {\n",
+    "    const canvas = document.getElementById('static');\n",
+    "    const ctx = canvas.getContext('2d');\n",
+    "    const w = canvas.width, h = canvas.height;\n",
+    "    \n",
+    "    const vertices = [\n",
+    "        [-1,-1,-1], [1,-1,-1], [1,1,-1], [-1,1,-1],\n",
+    "        [-1,-1, 1], [1,-1, 1], [1,1, 1], [-1,1, 1]\n",
+    "    ];\n",
+    "    const edges = [\n",
+    "        [0,1],[1,2],[2,3],[3,0],\n",
+    "        [4,5],[5,6],[6,7],[7,4],\n",
+    "        [0,4],[1,5],[2,6],[3,7]\n",
+    "    ];\n",
+    "    \n",
+    "    function project(x, y, z) {\n",
+    "        z += 4;  // push back so z > 0\n",
+    "        return [x/z * 100 + w/2, y/z * 100 + h/2];\n",
+    "    }\n",
+    "    \n",
+    "    ctx.strokeStyle = '#0f0';\n",
+    "    ctx.lineWidth = 2;\n",
+    "    \n",
+    "    for (const [i, j] of edges) {\n",
+    "        const [x1, y1] = project(...vertices[i]);\n",
+    "        const [x2, y2] = project(...vertices[j]);\n",
+    "        ctx.beginPath();\n",
+    "        ctx.moveTo(x1, y1);\n",
+    "        ctx.lineTo(x2, y2);\n",
+    "        ctx.stroke();\n",
+    "    }\n",
+    "})();\n",
+    "</script>\n",
+    "\"\"\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# spinning cube\n",
+    "\n",
+    "from IPython.display import HTML\n",
+    "\n",
+    "HTML(\"\"\"\n",
+    "<canvas id=\"spin\" width=\"300\" height=\"300\" style=\"background:#111\"></canvas>\n",
+    "<script>\n",
+    "(function() {\n",
+    "    const canvas = document.getElementById('spin');\n",
+    "    const ctx = canvas.getContext('2d');\n",
+    "    const w = canvas.width, h = canvas.height;\n",
+    "    \n",
+    "    const vertices = [\n",
+    "        [-1,-1,-1], [1,-1,-1], [1,1,-1], [-1,1,-1],\n",
+    "        [-1,-1, 1], [1,-1, 1], [1,1, 1], [-1,1, 1]\n",
+    "    ];\n",
+    "    const edges = [\n",
+    "        [0,1],[1,2],[2,3],[3,0],\n",
+    "        [4,5],[5,6],[6,7],[7,4],\n",
+    "        [0,4],[1,5],[2,6],[3,7]\n",
+    "    ];\n",
+    "    \n",
+    "    function rotateY(x, y, z, a) {\n",
+    "        const c = Math.cos(a), s = Math.sin(a);\n",
+    "        return [x*c - z*s, y, x*s + z*c];\n",
+    "    }\n",
+    "    \n",
+    "    function project(x, y, z) {\n",
+    "        z += 4;\n",
+    "        return [x/z * 100 + w/2, y/z * 100 + h/2];\n",
+    "    }\n",
+    "    \n",
+    "    let angle = 0;\n",
+    "    function draw() {\n",
+    "        ctx.fillStyle = '#111';\n",
+    "        ctx.fillRect(0, 0, w, h);\n",
+    "        ctx.strokeStyle = '#0f0';\n",
+    "        ctx.lineWidth = 2;\n",
+    "        \n",
+    "        for (const [i, j] of edges) {\n",
+    "            const a = rotateY(...vertices[i], angle);\n",
+    "            const b = rotateY(...vertices[j], angle);\n",
+    "            const [x1, y1] = project(...a);\n",
+    "            const [x2, y2] = project(...b);\n",
+    "            ctx.beginPath();\n",
+    "            ctx.moveTo(x1, y1);\n",
+    "            ctx.lineTo(x2, y2);\n",
+    "            ctx.stroke();\n",
+    "        }\n",
+    "        \n",
+    "        angle += 0.02;\n",
+    "        requestAnimationFrame(draw);\n",
+    "    }\n",
+    "    draw();\n",
+    "})();\n",
+    "</script>\n",
+    "\"\"\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "name": "python",
+   "version": "3.11.0"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}