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

4 files changed, 22 insertions, 0 deletions

diff --git a/source/blender/gpu/GPU_capabilities.h b/source/blender/gpu/GPU_capabilities.h
index 45c656b49be..0c054d4f264 100644
--- a/source/blender/gpu/GPU_capabilities.h
+++ b/source/blender/gpu/GPU_capabilities.h
@@ -37,6 +37,8 @@ int GPU_max_textures(void);
 int GPU_max_textures_vert(void);
 int GPU_max_textures_geom(void);
 int GPU_max_textures_frag(void);
+int GPU_max_work_group_count(int index);
+int GPU_max_work_group_size(int index);
 int GPU_max_uniforms_vert(void);
 int GPU_max_uniforms_frag(void);
 int GPU_max_batch_indices(void);
diff --git a/source/blender/gpu/intern/gpu_capabilities.cc b/source/blender/gpu/intern/gpu_capabilities.cc
index bedc9ad3092..c6e9dc210cb 100644
--- a/source/blender/gpu/intern/gpu_capabilities.cc
+++ b/source/blender/gpu/intern/gpu_capabilities.cc
@@ -82,6 +82,16 @@ int GPU_max_textures(void)
   return GCaps.max_textures;
 }
 
+int GPU_max_work_group_count(int index)
+{
+  return GCaps.max_work_group_count[index];
+}
+
+int GPU_max_work_group_size(int index)
+{
+  return GCaps.max_work_group_size[index];
+}
+
 int GPU_max_uniforms_vert(void)
 {
   return GCaps.max_uniforms_vert;
diff --git a/source/blender/gpu/intern/gpu_capabilities_private.hh b/source/blender/gpu/intern/gpu_capabilities_private.hh
index ee7ef1e69e6..95cf7fd335d 100644
--- a/source/blender/gpu/intern/gpu_capabilities_private.hh
+++ b/source/blender/gpu/intern/gpu_capabilities_private.hh
@@ -41,6 +41,8 @@ struct GPUCapabilities {
   int max_textures_vert = 0;
   int max_textures_geom = 0;
   int max_textures_frag = 0;
+  int max_work_group_count[3] = {0, 0, 0};
+  int max_work_group_size[3] = {0, 0, 0};
   int max_uniforms_vert = 0;
   int max_uniforms_frag = 0;
   int max_batch_indices = 0;
diff --git a/source/blender/gpu/opengl/gl_backend.cc b/source/blender/gpu/opengl/gl_backend.cc
index fb03a2c2d2a..d85f9f7684d 100644
--- a/source/blender/gpu/opengl/gl_backend.cc
+++ b/source/blender/gpu/opengl/gl_backend.cc
@@ -438,6 +438,14 @@ void GLBackend::capabilities_init()
   GCaps.mem_stats_support = GLEW_NVX_gpu_memory_info || GLEW_ATI_meminfo;
   GCaps.shader_image_load_store_support = GLEW_ARB_shader_image_load_store;
   GCaps.compute_shader_support = GLEW_ARB_compute_shader;
+  if (GCaps.compute_shader_support) {
+    glGetIntegeri_v(GL_MAX_COMPUTE_WORK_GROUP_COUNT, 0, &GCaps.max_work_group_count[0]);
+    glGetIntegeri_v(GL_MAX_COMPUTE_WORK_GROUP_COUNT, 1, &GCaps.max_work_group_count[1]);
+    glGetIntegeri_v(GL_MAX_COMPUTE_WORK_GROUP_COUNT, 2, &GCaps.max_work_group_count[2]);
+    glGetIntegeri_v(GL_MAX_COMPUTE_WORK_GROUP_SIZE, 0, &GCaps.max_work_group_size[0]);
+    glGetIntegeri_v(GL_MAX_COMPUTE_WORK_GROUP_SIZE, 1, &GCaps.max_work_group_size[1]);
+    glGetIntegeri_v(GL_MAX_COMPUTE_WORK_GROUP_SIZE, 2, &GCaps.max_work_group_size[2]);
+  }
   GCaps.shader_storage_buffer_objects_support = GLEW_ARB_shader_storage_buffer_object;
   /* GL specific capabilities. */
   glGetIntegerv(GL_MAX_3D_TEXTURE_SIZE, &GLContext::max_texture_3d_size);