Fix slow continuous depsgraph updates in sculpt paint mode in some cases

Updates for cursor could cause the paint data to be continuously refreshed,
which is pretty cheap by itself, but not when it starts tagging the depsgraph.

The paint slot refresh code ideally should not be doing depsgraph tags at all,
but checking if there were changes at least avoids continuous updates.

1 files changed, 35 insertions, 28 deletions

diff --git a/source/blender/blenkernel/intern/material.c b/source/blender/blenkernel/intern/material.c
index 6c6d2298dbd..51e27f173c8 100644
--- a/source/blender/blenkernel/intern/material.c
+++ b/source/blender/blenkernel/intern/material.c
@@ -1512,58 +1512,65 @@ static ePaintSlotFilter material_paint_slot_filter(const struct Object *ob)
 
 void BKE_texpaint_slot_refresh_cache(Scene *scene, Material *ma, const struct Object *ob)
 {
-  int count = 0;
-
   if (!ma) {
     return;
   }
 
   const ePaintSlotFilter slot_filter = material_paint_slot_filter(ob);
 
-  /* COW needed when adding texture slot on an object with no materials. */
-  DEG_id_tag_update(&ma->id, ID_RECALC_SHADING | ID_RECALC_COPY_ON_WRITE);
+  const TexPaintSlot *prev_texpaintslot = ma->texpaintslot;
+  const int prev_paint_active_slot = ma->paint_active_slot;
+  const int prev_paint_clone_slot = ma->paint_clone_slot;
+  const int prev_tot_slots = ma->tot_slots;
 
-  if (ma->texpaintslot) {
-    MEM_freeN(ma->texpaintslot);
-    ma->tot_slots = 0;
-    ma->texpaintslot = NULL;
-  }
+  ma->texpaintslot = NULL;
+  ma->tot_slots = 0;
 
   if (scene->toolsettings->imapaint.mode == IMAGEPAINT_MODE_IMAGE) {
     ma->paint_active_slot = 0;
     ma->paint_clone_slot = 0;
-    return;
   }
-
-  if (!(ma->nodetree)) {
+  else if (!(ma->nodetree)) {
     ma->paint_active_slot = 0;
     ma->paint_clone_slot = 0;
-    return;
   }
+  else {
+    int count = count_texture_nodes_recursive(ma->nodetree, slot_filter);
 
-  count = count_texture_nodes_recursive(ma->nodetree, slot_filter);
-
-  if (count == 0) {
-    ma->paint_active_slot = 0;
-    ma->paint_clone_slot = 0;
-    return;
-  }
+    if (count == 0) {
+      ma->paint_active_slot = 0;
+      ma->paint_clone_slot = 0;
+    }
+    else {
+      ma->texpaintslot = MEM_callocN(sizeof(*ma->texpaintslot) * count, "texpaint_slots");
 
-  ma->texpaintslot = MEM_callocN(sizeof(*ma->texpaintslot) * count, "texpaint_slots");
+      bNode *active_node = nodeGetActivePaintCanvas(ma->nodetree);
 
-  bNode *active_node = nodeGetActivePaintCanvas(ma->nodetree);
+      fill_texpaint_slots_recursive(ma->nodetree, active_node, ob, ma, count, slot_filter);
 
-  fill_texpaint_slots_recursive(ma->nodetree, active_node, ob, ma, count, slot_filter);
+      ma->tot_slots = count;
 
-  ma->tot_slots = count;
+      if (ma->paint_active_slot >= count) {
+        ma->paint_active_slot = count - 1;
+      }
 
-  if (ma->paint_active_slot >= count) {
-    ma->paint_active_slot = count - 1;
+      if (ma->paint_clone_slot >= count) {
+        ma->paint_clone_slot = count - 1;
+      }
+    }
   }
 
-  if (ma->paint_clone_slot >= count) {
-    ma->paint_clone_slot = count - 1;
+  /* COW needed when adding texture slot on an object with no materials.
+   * But do it only when slots actually change to avoid continuous depsgrap updates. */
+  if (ma->tot_slots != prev_tot_slots || ma->paint_active_slot != prev_paint_active_slot ||
+      ma->paint_clone_slot != prev_paint_clone_slot ||
+      (ma->texpaintslot && prev_texpaintslot &&
+       memcmp(ma->texpaintslot, prev_texpaintslot, sizeof(*ma->texpaintslot) * ma->tot_slots) !=
+           0)) {
+    DEG_id_tag_update(&ma->id, ID_RECALC_SHADING | ID_RECALC_COPY_ON_WRITE);
   }
+
+  MEM_SAFE_FREE(prev_texpaintslot);
 }
 
 void BKE_texpaint_slots_refresh_object(Scene *scene, struct Object *ob)