Move phase functions into a library

data/shaders/opengl/lib.glsl

@@ -12,6 +12,25 @@ struct Surface {
  float ambientOcclusion;
 };
 
+// Phase functions
+// https://www.scratchapixel.com/lessons/procedural-generation-virtual-worlds/simulating-sky/simulating-colors-of-the-sky.html
+float miePhaseFunction(const float g, const float mu)
+{
+ /*
+ * Mie phase function:
+ */
+ return 3.f / (8.f * 3.141592) * ((1.f - g * g) * (1.f + mu * mu)) / ((2.f + g * g) * pow(1.f + g * g - 2.f * g * mu, 1.5f));
+}
+
+float rayleighPhaseFunction(const float mu)
+{
+ /*
+ * Rayleigh phase function:
+ */
+ return 3.f / (16.f * 3.141592) * (1 + mu * mu);
+}
+
+
 // Currently used by: hopefully everything
 // Evaluates a standard blinn-phong diffuse+specular, with the addition of a
 // light intensity term to scale the lighting contribution based on (pre-calculated)

data/shaders/opengl/planetrings.frag

@@ -28,11 +28,11 @@ void main(void)
 
  // second term: diffuse mie (scattering through ring)
  float g = 0.76f;
- float phaseThrough = 3.f / (8.f * 3.141592) * ((1.f - g * g) * (1.f + mu * mu)) / ((2.f + g * g) * pow(1.f + g * g - 2.f * g * mu, 1.5f));
+ float phaseThrough = miePhaseFunction(g, mu);
 
  // third term: reflect mie (imitate albedo >= 1.0)
  float muRev = dot(-normalize(vec3(uLight[i].position)), eyenorm);
- float phaseReflect = 3.f / (8.f * 3.141592) * ((1.f - g * g) * (1.f + muRev * muRev)) / ((2.f + g * g) * pow(1.f + g * g - 2.f * g * muRev, 1.5f));
+ float phaseReflect = miePhaseFunction(g, muRev);
 
  col = col + texCol * (diffuse + phaseThrough + phaseReflect) * uLight[i].diffuse;
  }