Render: Use GHash for storing render parts

Previously, render parts were stored in a linked list and every tile update
searched the entire list for the correct part. As a result, the overhead
of searching tiles increased quadratically w.r.t. the number of tiles.

By hashing the parts based on their location, this operation is much faster,
significantly reducing the tile update overhead for small tiles and/or large
renders.

For example, rendering an empty scene in 1080p at 1spp and 8x8 tiles goes
down from 9.22sec to 1.45sec on my laptop.

Reviewers: brecht, sergey

Differential Revision: https://developer.blender.org/D4896

source/blender/render/intern/include/render_types.h

@@ -41,6 +41,7 @@ struct Main;
 struct Object;
 struct RenderEngine;
 struct ReportList;
+struct GHash;
 
 /* this is handed over to threaded hiding/passes/shading engine */
 typedef struct RenderPart {
@@ -112,7 +113,7 @@ struct Render {
   struct Object *camera_override;
 
   ThreadRWMutex partsmutex;
-  ListBase parts;
+  struct GHash *parts;
 
   /* render engine */
   struct RenderEngine *engine;

source/blender/render/intern/source/external_engine.c

@@ -29,9 +29,11 @@
 
 #include "BLT_translation.h"
 
-#include "BLI_listbase.h"
-#include "BLI_string.h"
 #include "BLI_utildefines.h"
+#include "BLI_ghash.h"
+#include "BLI_listbase.h"
+#include "BLI_rect.h"
+#include "BLI_string.h"
 
 #include "DNA_object_types.h"
 
@@ -169,18 +171,10 @@ void RE_engine_free(RenderEngine *engine)
 
 static RenderPart *get_part_from_result(Render *re, RenderResult *result)
 {
-  RenderPart *pa;
+  rcti key = result->tilerect;
+  BLI_rcti_translate(&key, re->disprect.xmin, re->disprect.ymin);
 
-  for (pa = re->parts.first; pa; pa = pa->next) {
-    if (result->tilerect.xmin == pa->disprect.xmin - re->disprect.xmin &&
-        result->tilerect.ymin == pa->disprect.ymin - re->disprect.ymin &&
-        result->tilerect.xmax == pa->disprect.xmax - re->disprect.xmin &&
-        result->tilerect.ymax == pa->disprect.ymax - re->disprect.ymin) {
-      return pa;
-    }
-  }
-
-  return NULL;
+  return BLI_ghash_lookup(re->parts, &key);
 }
 
 RenderResult *RE_engine_begin_result(
@@ -458,7 +452,6 @@ rcti *RE_engine_get_current_tiles(Render *re, int *r_total_tiles, bool *r_needs_
 {
   static rcti tiles_static[BLENDER_MAX_THREADS];
   const int allocation_step = BLENDER_MAX_THREADS;
-  RenderPart *pa;
   int total_tiles = 0;
   rcti *tiles = tiles_static;
   int allocation_size = BLENDER_MAX_THREADS;
@@ -467,13 +460,15 @@ rcti *RE_engine_get_current_tiles(Render *re, int *r_total_tiles, bool *r_needs_
 
   *r_needs_free = false;
 
-  if (re->engine && (re->engine->flag & RE_ENGINE_HIGHLIGHT_TILES) == 0) {
+  if (!re->parts || (re->engine && (re->engine->flag & RE_ENGINE_HIGHLIGHT_TILES) == 0)) {
     *r_total_tiles = 0;
     BLI_rw_mutex_unlock(&re->partsmutex);
     return NULL;
   }
 
-  for (pa = re->parts.first; pa; pa = pa->next) {
+  GHashIterator pa_iter;
+  GHASH_ITER (pa_iter, re->parts) {
+    RenderPart *pa = BLI_ghashIterator_getValue(&pa_iter);
     if (pa->status == PART_STATUS_IN_PROGRESS) {
       if (total_tiles >= allocation_size) {
         /* Just in case we're using crazy network rendering with more

source/blender/render/intern/source/initrender.c

@@ -31,6 +31,7 @@
 #include "MEM_guardedalloc.h"
 
 #include "BLI_math.h"
+#include "BLI_ghash.h"
 #include "BLI_blenlib.h"
 #include "BLI_utildefines.h"
 
@@ -245,7 +246,10 @@ void RE_GetCameraModelMatrix(Render *re, struct Object *camera, float r_mat[4][4
 
 void RE_parts_free(Render *re)
 {
-  BLI_freelistN(&re->parts);
+  if (re->parts) {
+    BLI_ghash_free(re->parts, NULL, MEM_freeN);
+    re->parts = NULL;
+  }
 }
 
 void RE_parts_clamp(Render *re)
@@ -262,6 +266,9 @@ void RE_parts_init(Render *re)
 
   RE_parts_free(re);
 
+  re->parts = BLI_ghash_new(
+      BLI_ghashutil_inthash_v4_p, BLI_ghashutil_inthash_v4_cmp, "render parts");
+
   /* this is render info for caller, is not reset when parts are freed! */
   re->i.totpart = 0;
   re->i.curpart = 0;
@@ -323,7 +330,7 @@ void RE_parts_init(Render *re)
       pa->rectx = rectx;
       pa->recty = recty;
 
-      BLI_addtail(&re->parts, pa);
+      BLI_ghash_insert(re->parts, &pa->disprect, pa);
       re->i.totpart++;
     }
   }

source/blender/render/intern/source/render_result.c

@@ -29,6 +29,7 @@
 #include "MEM_guardedalloc.h"
 
 #include "BLI_utildefines.h"
+#include "BLI_ghash.h"
 #include "BLI_listbase.h"
 #include "BLI_hash_md5.h"
 #include "BLI_path_util.h"
@@ -1174,13 +1175,14 @@ static void save_render_result_tile(RenderResult *rr, RenderResult *rrpart, cons
 
 void render_result_save_empty_result_tiles(Render *re)
 {
-  RenderPart *pa;
   RenderResult *rr;
   RenderLayer *rl;
 
   for (rr = re->result; rr; rr = rr->next) {
     for (rl = rr->layers.first; rl; rl = rl->next) {
-      for (pa = re->parts.first; pa; pa = pa->next) {
+      GHashIterator pa_iter;
+      GHASH_ITER (pa_iter, re->parts) {
+        RenderPart *pa = BLI_ghashIterator_getValue(&pa_iter);
         if (pa->status != PART_STATUS_MERGED) {
           int party = pa->disprect.ymin - re->disprect.ymin;
           int partx = pa->disprect.xmin - re->disprect.xmin;