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, 13 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_manager.h b/source/blender/draw/intern/draw_manager.h
index 84bc0327aa2..d4e22c83798 100644
--- a/source/blender/draw/intern/draw_manager.h
+++ b/source/blender/draw/intern/draw_manager.h
@@ -187,6 +187,10 @@ typedef enum {
   DRW_CMD_DRAW_INSTANCE = 2,
   DRW_CMD_DRAW_INSTANCE_RANGE = 3,
   DRW_CMD_DRAW_PROCEDURAL = 4,
+
+  /* Compute Commands. */
+  DRW_CMD_COMPUTE = 8,
+
   /* Other Commands */
   DRW_CMD_CLEAR = 12,
   DRW_CMD_DRWSTATE = 13,
@@ -224,6 +228,12 @@ typedef struct DRWCommandDrawInstanceRange {
   uint inst_count;
 } DRWCommandDrawInstanceRange;
 
+typedef struct DRWCommandCompute {
+  int groups_x_len;
+  int groups_y_len;
+  int groups_z_len;
+} DRWCommandCompute;
+
 typedef struct DRWCommandDrawProcedural {
   GPUBatch *batch;
   DRWResourceHandle handle;
@@ -260,6 +270,7 @@ typedef union DRWCommand {
   DRWCommandDrawInstance instance;
   DRWCommandDrawInstanceRange instance_range;
   DRWCommandDrawProcedural procedural;
+  DRWCommandCompute compute;
   DRWCommandSetMutableState state;
   DRWCommandSetStencil stencil;
   DRWCommandSetSelectID select_id;
@@ -274,6 +285,7 @@ struct DRWCallBuffer {
 };
 
 /** Used by #DRWUniform.type */
+/* TODO(jbakker): rename to DRW_RESOURCE/DRWResourceType. */
 typedef enum {
   DRW_UNIFORM_INT = 0,
   DRW_UNIFORM_INT_COPY,
@@ -286,6 +298,7 @@ typedef enum {
   DRW_UNIFORM_BLOCK,
   DRW_UNIFORM_BLOCK_REF,
   DRW_UNIFORM_TFEEDBACK_TARGET,
+  DRW_UNIFORM_VERTEX_BUFFER_AS_STORAGE,
   /** Per drawcall uniforms/UBO */
   DRW_UNIFORM_BLOCK_OBMATS,
   DRW_UNIFORM_BLOCK_OBINFOS,