Add entity shaders

shaders/entity.frag

@@ -0,0 +1,13 @@
+#version 430
+
+in vec2 fragTexCoord;
+in vec3 fragColor;
+
+uniform sampler2D circleTexture;
+
+out vec4 finalColor;
+
+void main() {
+    float alpha = texture(circleTexture, fragTexCoord).r;
+    finalColor = vec4(fragColor, alpha);
+}

shaders/entity.vert

@@ -0,0 +1,48 @@
+#version 430
+
+// quad corner position (-0.5 to 0.5)
+layout(location = 0) in vec2 position;
+layout(location = 1) in vec2 texCoord;
+
+// entity data from SSBO
+struct Entity {
+    float x;
+    float y;
+    uint color;
+};
+
+layout(std430, binding = 0) readonly buffer EntityData {
+    Entity entities[];
+};
+
+// screen size for NDC conversion
+uniform vec2 screenSize;
+
+out vec2 fragTexCoord;
+out vec3 fragColor;
+
+void main() {
+    // get entity data from SSBO
+    Entity e = entities[gl_InstanceID];
+
+    // 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;
+
+    // quad size in NDC (16 pixels)
+    float quadSizeNdc = 16.0 / screenSize.x;
+
+    // offset by quad corner position
+    gl_Position = vec4(ndcX + position.x * quadSizeNdc,
+                       ndcY + position.y * quadSizeNdc,
+                       0.0, 1.0);
+
+    // extract RGB from packed color (0xRRGGBB)
+    float r = float((e.color >> 16u) & 0xFFu) / 255.0;
+    float g = float((e.color >> 8u) & 0xFFu) / 255.0;
+    float b = float(e.color & 0xFFu) / 255.0;
+    fragColor = vec3(r, g, b);
+
+    fragTexCoord = texCoord;
+}