DrawManager: Use Compute Shader to Update Hair.

This patch will use compute shaders to create the VBO for hair.
The previous implementation uses transform feedback.

Timings before: between 0.000069s and 0.000362s.
Timings after:  between 0.000032s and 0.000092s.

Speedup isn't noticeable by end-users. The patch is used to test
the new compute shader pipeline and integrate it with the draw
manager. Allowing EEVEE, Workbench and other draw engines to
use compute shaders with the introduction of `DRW_shgroup_call_compute`
and `DRW_shgroup_vertex_buffer`.

Future improvements are possible by generating the index buffer
of hair directly on the GPU.

NOTE: that compute shaders aren't supported by Apple and still use
the transform feedback workaround.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D11057

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/draw/intern/DRW_render.h b/source/blender/draw/intern/DRW_render.h
index 2545cfa65dc..5071658fd82 100644
--- a/source/blender/draw/intern/DRW_render.h
+++ b/source/blender/draw/intern/DRW_render.h
@@ -438,6 +438,10 @@ void DRW_shgroup_call_range(
 void DRW_shgroup_call_instance_range(
     DRWShadingGroup *shgroup, Object *ob, struct GPUBatch *geom, uint i_sta, uint i_ct);
 
+void DRW_shgroup_call_compute(DRWShadingGroup *shgroup,
+                              int groups_x_len,
+                              int groups_y_len,
+                              int groups_z_len);
 void DRW_shgroup_call_procedural_points(DRWShadingGroup *sh, Object *ob, uint point_count);
 void DRW_shgroup_call_procedural_lines(DRWShadingGroup *sh, Object *ob, uint line_count);
 void DRW_shgroup_call_procedural_triangles(DRWShadingGroup *sh, Object *ob, uint tri_count);
@@ -575,6 +579,9 @@ void DRW_shgroup_uniform_vec4_array_copy(DRWShadingGroup *shgroup,
                                          const char *name,
                                          const float (*value)[4],
                                          int arraysize);
+void DRW_shgroup_vertex_buffer(DRWShadingGroup *shgroup,
+                               const char *name,
+                               struct GPUVertBuf *vertex_buffer);
 
 bool DRW_shgroup_is_empty(DRWShadingGroup *shgroup);