1 files changed, 38 insertions, 0 deletions
diff --git a/source/blender/draw/engines/eevee/shaders/random_lib.glsl b/source/blender/draw/engines/eevee/shaders/random_lib.glsl
new file mode 100644
index 00000000000..25a3e0f56b4
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+++ b/source/blender/draw/engines/eevee/shaders/random_lib.glsl
@@ -0,0 +1,38 @@
+
+/**
+ * Random numbers and low discrepency sequences utilities.
+ **/
+
+#pragma BLENDER_REQUIRE(common_math_lib.glsl)
+
+/* From: http://holger.dammertz.org/stuff/notes_HammersleyOnHemisphere.html */
+float van_der_corput_radical_inverse(uint bits)
+{
+  bits = (bits << 16u) | (bits >> 16u);
+  bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
+  bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
+  bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
+  bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
+  /* Same as dividing by 0x100000000. */
+  return float(bits) * 2.3283064365386963e-10;
+}
+
+vec2 hammersley_2d(float i, float sample_count)
+{
+  vec2 rand;
+  rand.x = i / sample_count;
+  rand.y = van_der_corput_radical_inverse(uint(i));
+  return rand;
+}
+
+/* This transform a 2d random sample (in [0..1] range) to a sample located on a cylinder of the
+ * same range. This is because the sampling functions expect such a random sample which is
+ * normally precomputed. */
+vec3 rand2d_to_cylinder(vec2 rand)
+{
+  float theta = rand.x;
+  float phi = (rand.y - 0.5) * M_2PI;
+  float cos_phi = cos(phi);
+  float sin_phi = sqrt(1.0 - sqr(cos_phi)) * sign(phi);
+  return vec3(theta, cos_phi, sin_phi);
+}