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examples/models/resources/shaders/irradiance.fs

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+/*******************************************************************************************
+*
+*   rPBR [shader] - Irradiance cubemap fragment shader
+*
+*   Copyright (c) 2017 Victor Fisac
+*
+**********************************************************************************************/
+
+#version 330
+
+# Input vertex attributes (from vertex shader)
+in vec3 fragPos
+
+# Input uniform values
+uniform samplerCube environmentMap
+
+# Constant values
+const float PI = 3.14159265359f
+
+# Output fragment color
+out vec4 finalColor
+
+void main()
+[
+    # The sample direction equals the hemisphere's orientation
+    vec3 normal = normalize(fragPos)
+
+    vec3 irradiance = vec3(0.0)
+
+    vec3 up = vec3(0.0, 1.0, 0.0)
+    vec3 right = cross(up, normal)
+    up = cross(normal, right)
+
+    float sampleDelta = 0.025f
+    float nrSamples = 0.0
+
+    for (float phi = 0.0 phi < 2.0*PI phi += sampleDelta)
+    [
+        for (float theta = 0.0 theta < 0.5*PI theta += sampleDelta)
+        [
+            # Spherical to cartesian (in tangent space)
+            vec3 tangentSample = vec3(sin(theta)*cos(phi), sin(theta)*sin(phi), cos(theta))
+            
+            # tangent space to world
+            vec3 sampleVec = tangentSample.x*right + tangentSample.y*up + tangentSample.z*normal
+
+            # Fetch color from environment cubemap
+            irradiance += texture(environmentMap, sampleVec).rgb*cos(theta)*sin(theta)
+            nrSamples++
+        ]
+    ]
+
+    # Calculate irradiance average value from samples
+    irradiance = PI*irradiance*(1.0/float(nrSamples))
+
+    # Calculate final fragment color
+    finalColor = vec4(irradiance, 1.0)
+]