Fixed render time regression in Blender Internal

It was caused by image threading safe commit and it was noticeable
only on really multi-core CPU (like dual-socket Xeon stations), was
not visible on core i7 machine.

The reason of slowdown was spinlock around image buffer referencing,
which lead to lots of cores waiting for single core and using image
buffer after it was referenced was not so much longer than doing
reference itself.

The most clear solution here seemed to be introducing Image Pool
which will contain list of loaded and referenced image buffers, so
all threads could skip lock if the pool is used for reading only.
Lock only needed in cases when buffer for requested image user is
missing in the pool. This lock will happen only once per image so
overall amount of locks is much less that it was before.

To operate with pool:
- BKE_image_pool_new() creates new pool
- BKE_image_pool_free() destroys pool and dereferences all image
  buffers which were loaded to it
- BKE_image_pool_acquire_ibuf() returns image buffer for given
  image and user. Pool could be NULL and in this case fallback to
  BKE_image_acquire_ibuf will happen.

  This helps to avoid lots to if(poll) checks in image sampling
  code.

- BKE_image_pool_release_ibuf releases image buffer. In fact, it
  will only do something if pool is NULL, in all other case it'll
  equal to DoNothing operation.

1 files changed, 2 insertions, 1 deletions

diff --git a/source/blender/editors/sculpt_paint/paint_intern.h b/source/blender/editors/sculpt_paint/paint_intern.h
index 75a95d4d6fd..faa9ce00da8 100644
--- a/source/blender/editors/sculpt_paint/paint_intern.h
+++ b/source/blender/editors/sculpt_paint/paint_intern.h
@@ -36,6 +36,7 @@ struct ARegion;
 struct bContext;
 struct bglMats;
 struct Brush;
+struct ImagePool;
 struct ListBase;
 struct Mesh;
 struct Object;
@@ -140,7 +141,7 @@ void paint_calc_redraw_planes(float planes[4][4],
 
 void projectf(struct bglMats *mats, const float v[3], float p[2]);
 float paint_calc_object_space_radius(struct ViewContext *vc, const float center[3], float pixel_radius);
-float paint_get_tex_pixel(struct Brush *br, float u, float v);
+float paint_get_tex_pixel(struct Brush *br, float u, float v, struct ImagePool *pool);
 int imapaint_pick_face(struct ViewContext *vc, const int mval[2], unsigned int *index, unsigned int totface);
 void imapaint_pick_uv(struct Scene *scene, struct Object *ob, unsigned int faceindex, const int xy[2], float uv[2]);