[Bf-blender-cvs] [21eeedfc60b] blender-v3.4-release: Fix T101562: GPU: Update fmod to match Cycles/OSL behavior

[Miguel Pozo]

Commit: 21eeedfc60b5ea8603a5c74235e736c9d0378aa8
Author: Miguel Pozo
Date:   Tue Nov 15 13:04:47 2022 +0100
Branches: blender-v3.4-release
https://developer.blender.org/rB21eeedfc60b5ea8603a5c74235e736c9d0378aa8

Fix T101562: GPU: Update fmod to match Cycles/OSL behavior

Implementation from:
https://github.com/AcademySoftwareFoundation/OpenShadingLanguage/blob/main/src/include/OSL/dual.h#L1283
https://github.com/OpenImageIO/oiio/blob/master/src/include/OpenImageIO/fmath.h#L1605

Reviewed By: fclem

Maniphest Tasks: T101562

Differential Revision: https://developer.blender.org/D16497

===================================================================

M	source/blender/gpu/shaders/common/gpu_shader_common_math_utils.glsl

===================================================================

diff --git a/source/blender/gpu/shaders/common/gpu_shader_common_math_utils.glsl b/source/blender/gpu/shaders/common/gpu_shader_common_math_utils.glsl
index 47f8e26db0b..ca9c42f2027 100644
--- a/source/blender/gpu/shaders/common/gpu_shader_common_math_utils.glsl
+++ b/source/blender/gpu/shaders/common/gpu_shader_common_math_utils.glsl
@@ -5,11 +5,14 @@ float safe_divide(float a, float b)
   return (b != 0.0) ? a / b : 0.0;
 }
 
-/* fmod function compatible with OSL using nvidia reference example. */
+/* fmod function compatible with OSL (copy from OSL/dual.h) */
 float compatible_fmod(float a, float b)
 {
-  float c = (b != 0.0) ? fract(abs(a / b)) * abs(b) : 0.0;
-  return (a < 0.0) ? -c : c;
+  if (b != 0.0f) {
+    int N = int(a / b);
+    return a - N * b;
+  }
+  return 0.0f;
 }
 
 float compatible_pow(float x, float y)