Fix T94881: GPU subdivision fails with high polycount coarse meshes

Coarse meshes with high polycount would show as corrupted when GPU
subdivision is used with AMD cards This was caused by the OpenSubdiv
library not taking `GL_MAX_COMPUTE_WORK_GROUP_COUNT` into account when
dispatching computes. AMD drivers tend to set the limit lower than
NVidia ones (2^16 for the former, and 2^32 for the latter, at least
on my machine).

This moves the `GLComputeEvaluator` from the OpenSubdiv library into
`intern/opensubdiv` and modifies it to compute a dispatch size in a
similar way as for the draw code: we split the dispatch size into a 2
dimensional value based on `GL_MAX_COMPUTE_WORK_GROUP_COUNT` and
manually compute an index in the shader.

We could have patched the OpenSubdiv library and sent the fix upstream
(which can still be done), however, moving it to our side allows us to
better control the `GLComputeEvaluator` and in the future remove some
redundant work that it does compared to Blender (see T94644) and
probably prepare the ground for Vulkan support. As a matter of fact,
this patch also removes the OpenGL initialization that OpenSubdiv would
do here. This removal is not related to the bug fix, but necessary to not
have to copy more files/code over.

Differential Revision: https://developer.blender.org/D14131

1 files changed, 1 insertions, 3 deletions

diff --git a/intern/opensubdiv/internal/evaluator/eval_output_gpu.h b/intern/opensubdiv/internal/evaluator/eval_output_gpu.h
index 783efd484aa..dc137e4322e 100644
--- a/intern/opensubdiv/internal/evaluator/eval_output_gpu.h
+++ b/intern/opensubdiv/internal/evaluator/eval_output_gpu.h
@@ -20,13 +20,11 @@
 #define OPENSUBDIV_EVAL_OUTPUT_GPU_H_
 
 #include "internal/evaluator/eval_output.h"
+#include "internal/evaluator/gl_compute_evaluator.h"
 
-#include <opensubdiv/osd/glComputeEvaluator.h>
 #include <opensubdiv/osd/glPatchTable.h>
 #include <opensubdiv/osd/glVertexBuffer.h>
 
-using OpenSubdiv::Osd::GLComputeEvaluator;
-using OpenSubdiv::Osd::GLStencilTableSSBO;
 using OpenSubdiv::Osd::GLVertexBuffer;
 
 namespace blender {