Fixes T91632 by stopping the sample correlation between dimensions which was causing rendering artifacts on simple scenes.

Fix T91632: Stops the sample correlation between dimensions which was causing rendering artefacts on simple scenes.

This is done by increasing the amount of jitter the Cranley Patterson Rotation is allowed to add. Also, it uses the y dimension of the of the sample table for 1D sampling which causes further decorrelation between dimensions. As an additional measure the x and y dimensions are swapped randomly to provide further decorrelation.

Maniphest Tasks: T91632

Differential Revision: https://developer.blender.org/D12610

1 files changed, 15 insertions, 17 deletions

diff --git a/intern/cycles/kernel/kernel_jitter.h b/intern/cycles/kernel/kernel_jitter.h
index 354e8115538..ab38895da54 100644
--- a/intern/cycles/kernel/kernel_jitter.h
+++ b/intern/cycles/kernel/kernel_jitter.h
@@ -74,10 +74,6 @@ ccl_device_inline float cmj_randfloat_simple(uint i, uint p)
 
 ccl_device float pmj_sample_1D(const KernelGlobals *kg, uint sample, uint rng_hash, uint dimension)
 {
-  /* The PMJ sample sets contain a sample with (x,y) with NUM_PMJ_SAMPLES so for 1D
-   *  the x part is used as the sample (TODO(@leesonw): Add using both x and y parts
-   * independently). */
-
   /* Perform Owen shuffle of the sample number to reorder the samples. */
 #ifdef _SIMPLE_HASH_
   const uint rv = cmj_hash_simple(dimension, rng_hash);
@@ -95,7 +91,10 @@ ccl_device float pmj_sample_1D(const KernelGlobals *kg, uint sample, uint rng_ha
   const uint sample_set = s / NUM_PMJ_SAMPLES;
   const uint d = (dimension + sample_set);
   const uint dim = d % NUM_PMJ_PATTERNS;
-  int index = 2 * (dim * NUM_PMJ_SAMPLES + (s % NUM_PMJ_SAMPLES));
+  
+  /* The PMJ sample sets contain a sample with (x,y) with NUM_PMJ_SAMPLES so for 1D
+   *  the x part is used for even dims and the y for odd. */
+  int index = 2 * ((dim >> 1) * NUM_PMJ_SAMPLES + (s % NUM_PMJ_SAMPLES)) + (dim & 1);
 
   float fx = kernel_tex_fetch(__sample_pattern_lut, index);
 
@@ -104,12 +103,11 @@ ccl_device float pmj_sample_1D(const KernelGlobals *kg, uint sample, uint rng_ha
 #  ifdef _SIMPLE_HASH_
   float dx = cmj_randfloat_simple(d, rng_hash);
 #  else
-  /* Only jitter within the grid interval. */
   float dx = cmj_randfloat(d, rng_hash);
 #  endif
-  fx = fx + dx * (1.0f / NUM_PMJ_SAMPLES);
+  /* Jitter sample locations and map back into [0 1]. */
+  fx = fx + dx;
   fx = fx - floorf(fx);
-
 #else
 #  warning "Not using Cranley-Patterson Rotation."
 #endif
@@ -136,12 +134,12 @@ ccl_device void pmj_sample_2D(
   /* Based on the sample number a sample pattern is selected and offset by the dimension. */
   const uint sample_set = s / NUM_PMJ_SAMPLES;
   const uint d = (dimension + sample_set);
-  const uint dim = d % NUM_PMJ_PATTERNS;
+  uint dim = d % NUM_PMJ_PATTERNS;
   int index = 2 * (dim * NUM_PMJ_SAMPLES + (s % NUM_PMJ_SAMPLES));
 
   float fx = kernel_tex_fetch(__sample_pattern_lut, index);
   float fy = kernel_tex_fetch(__sample_pattern_lut, index + 1);
-
+  
 #ifndef _NO_CRANLEY_PATTERSON_ROTATION_
   /* Use Cranley-Patterson rotation to displace the sample pattern. */
 #  ifdef _SIMPLE_HASH_
@@ -151,17 +149,17 @@ ccl_device void pmj_sample_2D(
   float dx = cmj_randfloat(d, rng_hash);
   float dy = cmj_randfloat(d + 1, rng_hash);
 #  endif
-  /* Only jitter within the grid cells. */
-  fx = fx + dx * (1.0f / NUM_PMJ_DIVISIONS);
-  fy = fy + dy * (1.0f / NUM_PMJ_DIVISIONS);
-  fx = fx - floorf(fx);
-  fy = fy - floorf(fy);
+  /* Jitter sample locations and map back to the unit square [0 1]x[0 1]. */
+  float sx = fx + dx;
+  float sy = fy + dy;
+  sx = sx - floorf(sx);
+  sy = sy - floorf(sy);
 #else
 #  warning "Not using Cranley Patterson Rotation."
 #endif
 
-  (*x) = fx;
-  (*y) = fy;
+  (*x) = sx;
+  (*y) = sy;
 }
 
 CCL_NAMESPACE_END