OpenSubDiv: add support for an OpenGL evaluator

This evaluator is used in order to evaluate subdivision at render time, allowing for
faster renders of meshes with a subdivision surface modifier placed at the last
position in the modifier list.

When evaluating the subsurf modifier, we detect whether we can delegate evaluation
to the draw code. If so, the subdivision is first evaluated on the GPU using our own
custom evaluator (only the coarse data needs to be initially sent to the GPU), then,
buffers for the final `MeshBufferCache` are filled on the GPU using a set of
compute shaders. However, some buffers are still filled on the CPU side, if doing so
on the GPU is impractical (e.g. the line adjacency buffer used for x-ray, whose
logic is hardly GPU compatible).

This is done at the mesh buffer extraction level so that the result can be readily used
in the various OpenGL engines, without having to write custom geometry or tesselation
shaders.

We use our own subdivision evaluation shaders, instead of OpenSubDiv's vanilla one, in
order to control the data layout, and interpolation. For example, we store vertex colors
as compressed 16-bit integers, while OpenSubDiv's default evaluator only work for float
types.

In order to still access the modified geometry on the CPU side, for use in modifiers
or transform operators, a dedicated wrapper type is added `MESH_WRAPPER_TYPE_SUBD`.
Subdivision will be lazily evaluated via `BKE_object_get_evaluated_mesh` which will
create such a wrapper if possible. If the final subdivision surface is not needed on
the CPU side, `BKE_object_get_evaluated_mesh_no_subsurf` should be used.

Enabling or disabling GPU subdivision can be done through the user preferences (under
Viewport -> Subdivision).

See patch description for benchmarks.

Reviewed By: campbellbarton, jbakker, fclem, brecht, #eevee_viewport

Differential Revision: https://developer.blender.org/D12406

1 files changed, 6 insertions, 1 deletions

diff --git a/source/blender/gpu/GPU_vertex_buffer.h b/source/blender/gpu/GPU_vertex_buffer.h
index 62a495abfb3..43a8e7fc4cb 100644
--- a/source/blender/gpu/GPU_vertex_buffer.h
+++ b/source/blender/gpu/GPU_vertex_buffer.h
@@ -91,6 +91,8 @@ void GPU_vertbuf_handle_ref_remove(GPUVertBuf *verts);
 
 void GPU_vertbuf_init_with_format_ex(GPUVertBuf *, const GPUVertFormat *, GPUUsageType);
 
+void GPU_vertbuf_init_build_on_device(GPUVertBuf *verts, GPUVertFormat *format, uint v_len);
+
 #define GPU_vertbuf_init_with_format(verts, format) \
   GPU_vertbuf_init_with_format_ex(verts, format, GPU_USAGE_STATIC)
 
@@ -172,6 +174,7 @@ const GPUVertFormat *GPU_vertbuf_get_format(const GPUVertBuf *verts);
 uint GPU_vertbuf_get_vertex_alloc(const GPUVertBuf *verts);
 uint GPU_vertbuf_get_vertex_len(const GPUVertBuf *verts);
 GPUVertBufStatus GPU_vertbuf_get_status(const GPUVertBuf *verts);
+void GPU_vertbuf_tag_dirty(GPUVertBuf *verts);
 
 /**
  * Should be rename to #GPU_vertbuf_data_upload.
@@ -179,12 +182,14 @@ GPUVertBufStatus GPU_vertbuf_get_status(const GPUVertBuf *verts);
 void GPU_vertbuf_use(GPUVertBuf *);
 void GPU_vertbuf_bind_as_ssbo(struct GPUVertBuf *verts, int binding);
 
+void GPU_vertbuf_wrap_handle(GPUVertBuf *verts, uint64_t handle);
+
 /**
  * XXX: do not use!
  * This is just a wrapper for the use of the Hair refine workaround.
  * To be used with #GPU_vertbuf_use().
  */
-void GPU_vertbuf_update_sub(GPUVertBuf *verts, uint start, uint len, void *data);
+void GPU_vertbuf_update_sub(GPUVertBuf *verts, uint start, uint len, const void *data);
 
 /* Metrics */
 uint GPU_vertbuf_get_memory_usage(void);