WIP

shaders/ecs_billboard.vert

@@ -0,0 +1,30 @@
+// ECS billboard instanced vertex shader.
+// Per-instance: camera-relative position and size.
+// UVs are generated per-corner from gl_VertexID.
+layout(location = 0) in vec3  i_position;
+layout(location = 1) in float i_size;
+
+out vec2 f_uv;
+out vec4 f_pos;
+
+#include <common>
+
+const vec2 corners[6] = vec2[6](
+    vec2(-0.5, -0.5), vec2( 0.5, -0.5), vec2( 0.5,  0.5),
+    vec2(-0.5, -0.5), vec2( 0.5,  0.5), vec2(-0.5,  0.5)
+);
+const vec2 uvs[6] = vec2[6](
+    vec2(0.0, 0.0), vec2(1.0, 0.0), vec2(1.0, 1.0),
+    vec2(0.0, 0.0), vec2(1.0, 1.0), vec2(0.0, 1.0)
+);
+
+void main()
+{
+    int idx = gl_VertexID;
+    vec3 right = vec3(inv_view[0]);
+    vec3 up    = vec3(inv_view[1]);
+    vec3 worldPos = i_position + (right * corners[idx].x + up * corners[idx].y) * i_size;
+    f_pos       = modelview * vec4(worldPos, 1.0);
+    gl_Position = projection * f_pos;
+    f_uv        = uvs[idx];
+}