GPU: Add remarks about point topology

include/SDL3/SDL_gpu.h

@@ -515,6 +515,13 @@ typedef struct SDL_GPUFence SDL_GPUFence;
 /**
  * Specifies the primitive topology of a graphics pipeline.
  *
+ * If you are using POINTLIST you must include a point size output in the vertex shader.
+ * For HLSL compiling to SPIRV you must decorate a float output with [[vk::builtin("PointSize")]].
+ * FOR GLSL you must set the gl_PointSize builtin.
+ * For MSL you must include a float output with the [[point_size]] decorator.
+ * Note that sized point topology is totally unsupported on D3D12. Any size other than 1 will be ignored.
+ * In general, you should avoid using point topology for both compatibility and performance reasons. You WILL regret using it.
+ *
  * \since This enum is available since SDL 3.1.3
  *
  * \sa SDL_CreateGPUGraphicsPipeline