Draw instances from the GPU culling with indirect draws, occlusion culling and a depth prepass

shaders/depthprepass_alpha.frag

@@ -0,0 +1,16 @@
+// depth prepass of materials whose colour shader tests the alpha of the diffuse texture against the opacity of the
+// material (mat_default.frag and the like). the test here is stricter by one step of 8-bit alpha: a fragment which writes
+// depth here is never discarded by the colour pass, which would leave a hole with nothing drawn behind it
+
+in vec2 f_coord;
+
+#include <common>
+
+#texture (diffuse, 0, sRGB_A)
+uniform sampler2D diffuse;
+
+void main()
+{
+	if (texture(diffuse, f_coord).a < opacity + 1.0 / 255.0)
+		discard;
+}