Cycles: Scrambling distance for the PMJ sampler

Adds scrambling distance to the PMJ sampler. This is based
on the work by Mathieu Menuet in D12318 who created the original
implementation for the Sobol sampler.

Reviewed By: brecht

Maniphest Tasks: T92181

Differential Revision: https://developer.blender.org/D12854

1 files changed, 3 insertions, 33 deletions

diff --git a/intern/cycles/integrator/tile.cpp b/intern/cycles/integrator/tile.cpp
index b49e1b27b83..4a1558cce09 100644
--- a/intern/cycles/integrator/tile.cpp
+++ b/intern/cycles/integrator/tile.cpp
@@ -74,39 +74,9 @@ TileSize tile_calculate_best_size(const int2 &image_size,
   TileSize tile_size;
   const int num_path_states_per_sample = max_num_path_states / num_samples;
   if (scrambling_distance < 0.9f) {
-    /* Prefer large tiles for scrambling distance. */
-    if (image_size.x * image_size.y <= num_path_states_per_sample) {
-      tile_size.width = image_size.x;
-      tile_size.height = image_size.y;
-    }
-    else {
-      /* Pick the option with the biggest tile size */
-      int heightOption = num_path_states_per_sample / image_size.x;
-      int widthOption = num_path_states_per_sample / image_size.y;
-      // Check if these options are possible
-      if ((heightOption > 0) || (widthOption > 0)) {
-        int area1 = image_size.x * heightOption;
-        int area2 = widthOption * image_size.y;
-        /* The option with the biggest pixel area */
-        if (area1 >= area2) {
-          tile_size.width = image_size.x;
-          tile_size.height = heightOption;
-        }
-        else {
-          tile_size.width = widthOption;
-          tile_size.height = image_size.y;
-        }
-      }
-      else {  // Large tiles are not an option so use square tiles
-        if (num_path_states_per_sample != 0) {
-          tile_size.width = round_down_to_power_of_two(lround(sqrt(num_path_states_per_sample)));
-          tile_size.height = tile_size.width;
-        }
-        else {
-          tile_size.width = tile_size.height = 1;
-        }
-      }
-    }
+    /* Prefer large tiles for scrambling distance, bounded by max num path states. */
+    tile_size.width = min(image_size.x, max_num_path_states);
+    tile_size.height = min(image_size.y, max(max_num_path_states / tile_size.width, 1));
   }
   else {
     /* Calculate tile size as if it is the most possible one to fit an entire range of samples.