Fix T51133: Bad performance with texture painting depending on multi-thread settings.

This is more of a temp urgent hack than a proper fix, chenages required
for the later are too involved for 2.80 at that point of time and will
be done later.

That commit merely keeps the whole existing logic for 3D painting
textures, but instead of re-creating a pool of threads for *every* (!)
stroke evaluation (i.e. mouse move event during painting), we instead
use Blender's task scheduler.

That remains sub-optimal, there are likely more improvements possible in
that code, but it should address the main issue reported (which is
presumably caused by  windows thread launching being rather heavy process).

1 files changed, 19 insertions, 14 deletions

diff --git a/source/blender/editors/sculpt_paint/paint_image_proj.c b/source/blender/editors/sculpt_paint/paint_image_proj.c
index 303c3fac363..90ef64b01b7 100644
--- a/source/blender/editors/sculpt_paint/paint_image_proj.c
+++ b/source/blender/editors/sculpt_paint/paint_image_proj.c
@@ -40,6 +40,7 @@
 #include "BLI_math_bits.h"
 #include "BLI_math_color_blend.h"
 #include "BLI_memarena.h"
+#include "BLI_task.h"
 #include "BLI_threads.h"
 #include "BLI_utildefines.h"
 
@@ -5103,7 +5104,9 @@ static void image_paint_partial_redraw_expand(ImagePaintPartialRedraw *cell,
 }
 
 /* run this for single and multithreaded painting */
-static void *do_projectpaint_thread(void *ph_v)
+static void do_projectpaint_thread(TaskPool *__restrict UNUSED(pool),
+                                   void *ph_v,
+                                   int UNUSED(threadid))
 {
   /* First unpack args from the struct */
   ProjPaintState *ps = ((ProjectHandle *)ph_v)->ps;
@@ -5535,8 +5538,6 @@ static void *do_projectpaint_thread(void *ph_v)
 
     BLI_memarena_free(softenArena);
   }
-
-  return NULL;
 }
 
 static bool project_paint_op(void *state, const float lastpos[2], const float pos[2])
@@ -5546,20 +5547,22 @@ static bool project_paint_op(void *state, const float lastpos[2], const float po
   bool touch_any = false;
 
   ProjectHandle handles[BLENDER_MAX_THREADS];
-  ListBase threads;
+  TaskScheduler *scheduler = NULL;
+  TaskPool *task_pool = NULL;
   int a, i;
 
-  struct ImagePool *pool;
+  struct ImagePool *image_pool;
 
   if (!project_bucket_iter_init(ps, pos)) {
     return touch_any;
   }
 
   if (ps->thread_tot > 1) {
-    BLI_threadpool_init(&threads, do_projectpaint_thread, ps->thread_tot);
+    scheduler = BLI_task_scheduler_get();
+    task_pool = BLI_task_pool_create_suspended(scheduler, NULL);
   }
 
-  pool = BKE_image_pool_new();
+  image_pool = BKE_image_pool_new();
 
   /* get the threads running */
   for (a = 0; a < ps->thread_tot; a++) {
@@ -5588,21 +5591,23 @@ static bool project_paint_op(void *state, const float lastpos[2], const float po
              sizeof(ImagePaintPartialRedraw) * PROJ_BOUNDBOX_SQUARED);
     }
 
-    handles[a].pool = pool;
+    handles[a].pool = image_pool;
 
-    if (ps->thread_tot > 1) {
-      BLI_threadpool_insert(&threads, &handles[a]);
+    if (task_pool != NULL) {
+      BLI_task_pool_push(
+          task_pool, do_projectpaint_thread, &handles[a], false, TASK_PRIORITY_HIGH);
     }
   }
 
-  if (ps->thread_tot > 1) { /* wait for everything to be done */
-    BLI_threadpool_end(&threads);
+  if (task_pool != NULL) { /* wait for everything to be done */
+    BLI_task_pool_work_and_wait(task_pool);
+    BLI_task_pool_free(task_pool);
   }
   else {
-    do_projectpaint_thread(&handles[0]);
+    do_projectpaint_thread(NULL, &handles[0], 0);
   }
 
-  BKE_image_pool_free(pool);
+  BKE_image_pool_free(image_pool);
 
   /* move threaded bounds back into ps->projectPartialRedraws */
   for (i = 0; i < ps->image_tot; i++) {