GPUShader/DRW: Add Transform Feedback support.

This is a usefull feature that can be used to do a lot of precomputation on
the GPU instead of the CPU.

Implementation is simple and only covers the most usefull case.

How to use:
- Create shader with transform feedback.
- Create a pass with DRW_STATE_TRANS_FEEDBACK.
- Create a target Gwn_VertBuf (make sure it's big enough).
- Create a shading group with DRW_shgroup_transform_feedback_create().
- Add your draw calls to the shading group.
- Render your pass normaly.

Current limitation:
- Only one output buffer.
- Cannot pause/resume tfb rendering to interleave with normal drawcalls.
- Cannot get the number of verts drawn.

1 files changed, 8 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_manager_shader.c b/source/blender/draw/intern/draw_manager_shader.c
index 06a579c2208..77fcb766743 100644
--- a/source/blender/draw/intern/draw_manager_shader.c
+++ b/source/blender/draw/intern/draw_manager_shader.c
@@ -295,6 +295,14 @@ GPUShader *DRW_shader_create_with_lib(
 	return sh;
 }
 
+GPUShader *DRW_shader_create_with_transform_feedback(
+        const char *vert, const char *geom, const char *defines,
+        const GPUShaderTFBType prim_type, const char **varying_names, const int varying_count)
+{
+	return GPU_shader_create_ex(vert, NULL, geom, NULL, defines, GPU_SHADER_FLAGS_NONE,
+	                            prim_type, varying_names, varying_count);
+}
+
 GPUShader *DRW_shader_create_2D(const char *frag, const char *defines)
 {
 	return GPU_shader_create(datatoc_gpu_shader_2D_vert_glsl, frag, NULL, NULL, defines);