EEVEE: Motion Blur: Add accumulation motion blur for better precision

This revisit the render pipeline to support time slicing for better motion
blur.

We support accumulation with or without the Post-process motion blur.

If using the post-process, we reuse last step next motion data to avoid
another scene reevaluation.

This also adds support for hair motion blur which is handled in a similar
way as mesh motion blur.

The total number of samples is distributed evenly accross all timesteps to
avoid sampling weighting issues. For this reason, the sample count is
(internally) rounded up to the next multiple of the step count.

Only FX Motion BLur: {F8632258}

FX Motion Blur + 4 time steps: {F8632260}

FX Motion Blur + 32 time steps: {F8632261}

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D8079

1 files changed, 13 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_manager.c b/source/blender/draw/intern/draw_manager.c
index 55dc1d6c5d7..5b1276d0d6b 100644
--- a/source/blender/draw/intern/draw_manager.c
+++ b/source/blender/draw/intern/draw_manager.c
@@ -1942,6 +1942,19 @@ void DRW_custom_pipeline(DrawEngineType *draw_engine_type,
 #endif
 }
 
+/* Used when the render engine want to redo another cache populate inside the same render frame. */
+void DRW_cache_restart(void)
+{
+  /* Force cache to reset. */
+  drw_viewport_cache_resize();
+
+  drw_viewport_var_init();
+
+  DST.buffer_finish_called = false;
+
+  DRW_hair_init();
+}
+
 static struct DRWSelectBuffer {
   struct GPUFrameBuffer *framebuffer_depth_only;
   struct GPUTexture *texture_depth;