Begin work on glitter

1 files changed, 74 insertions, 0 deletions

diff --git a/glitter.slang b/glitter.slang
new file mode 100644
index 0000000..5442a0f
--- /dev/null
+++ b/glitter.slang
@@ -0,0 +1,74 @@
+#ifndef __GLITTER_INC
+#define __GLITTER_INC
+
+#define PI 3.1415926535897932384626433832795028841971
+
+float gaussian(float3 x, float3 mu, float sigma) {
+  float3 x_minus_mu = x - mu;
+  return exp(-dot(x_minus_mu, x_minus_mu) / (2 * sigma * sigma)) / (sigma * sqrt(2 * PI));
+}
+
+float det(float2x2 m) {
+  return m[0][0] * m[1][1] - m[0][1] * m[1][0];
+}
+
+float dirac(float3 x) {
+  // Ternary operator short-circuits in slang >:(
+  return any(abs(x) < 1e-4) ? 1e4 : 0;
+}
+
+// Maps a point on the unit hemisphere to an inscribed circle.
+float2 hemisphere_to_inscribed_circle(float3 p) {
+  // TODO
+  return 0;
+}
+
+float3 rand3_hash(float3 p)
+{
+    // Improved Murmurhash3 by Squirrel Eiserloh (GDC 2017)
+    p = float3(dot(p, float3(127.1, 311.7, 74.7)),
+               dot(p, float3(269.5, 183.3, 246.1)),
+               dot(p, float3(113.5, 271.9, 124.6)));
+    return -1.0 + 2.0 * frac(sin(p) * 43758.5453123);
+}
+
+public float D_Kemppinen(
+  float3 worldPos,
+  float3 H_tan,  // halfway vector in tangent space
+  float amount,
+  float roughness)
+{
+  float2x2 J_T__omega_h = 0;  // TODO
+  float det_J_T__omega_h = det(J_T__omega_h);
+  
+  float sum = 0;
+  // x is the current world space position.
+  float3 x = worldPos;
+  // omega_h is the halfway vector *in TBN coordinates.*
+  float3 omega_h = H_tan;
+  float3 T_omega_h = float3(
+      hemisphere_to_inscribed_circle(omega_h),
+      0);
+  uint K_p = 1;  // TODO
+  for (uint i = 0; i < K_p; ++i) {
+    // x_i is the position of the facet.
+    float3 x_i = worldPos;  // TODO randomize position
+    // mu_i is the orientation of the facet.
+    float3 mu_i = abs(rand3_hash(x_i));
+
+    float a_star = roughness;
+
+    float cur_gauss = gaussian(
+        T_omega_h,
+        mu_i,
+        a_star * sqrt(det_J_T__omega_h));
+
+    sum += cur_gauss * dirac(x_i - x);
+  }
+
+  float scale = det_J_T__omega_h / K_p;
+  return sum * scale;
+}
+
+#endif  // __GLITTER_INC
+