X-Git-Url: http://git.lukelau.me/?p=opengl.git;a=blobdiff_plain;f=prefilterfrag.glsl;fp=prefilterfrag.glsl;h=87cd70e4dae93209cbd03d598fa57baefbd9b748;hp=0000000000000000000000000000000000000000;hb=d80972d96e5fcd444657f937ab2700039efa83d2;hpb=9e43c799021b7bcca324b988aae44e98b05d10b4

diff --git a/prefilterfrag.glsl b/prefilterfrag.glsl
new file mode 100644
index 0000000..87cd70e
--- /dev/null
+++ b/prefilterfrag.glsl
@@ -0,0 +1,67 @@
+#version 330
+
+in vec3 localPos, normal;
+out vec4 fragColor;
+
+uniform samplerCube environmentMap;
+uniform float roughness;
+
+const float PI = 3.14159265359;
+
+//TODO: Put this in a separate shader program
+float radicalInverse(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);
+    return float(bits) * 2.3283064365386963e-10;
+}
+
+vec2 hammersley(uint i, uint N) {
+	return vec2(float(i) / float(N), radicalInverse(i));
+}
+
+vec3 importanceSampleGGX(vec2 Xi, vec3 N, float roughness) {
+	float a = roughness * roughness;
+
+	float phi = 2.f * PI * Xi.x;
+	float cosTheta = sqrt((1.f - Xi.y) / (1.f + (a * a - 1.f) * Xi.y));
+	float sinTheta = sqrt(1.f - cosTheta * cosTheta);
+
+	// spherical -> cartesian
+	vec3 H = vec3(cos(phi) * sinTheta, sin(phi) * sinTheta, cosTheta);
+
+	vec3 up = abs(N.z) < 0.999 ? vec3(0, 0, 1) : vec3(1, 0, 0);
+	vec3 tangent = normalize(cross(up, N));
+	vec3 bitangent = cross(N, tangent);
+
+	vec3 sampleVec = tangent * H.x + bitangent * H.y + N * H.z;
+	return normalize(sampleVec);
+}
+
+void main() {
+	vec3 N = normalize(localPos);
+
+	// approximate view direction - no grazing specular reflections
+	vec3 R = N;
+	vec3 V = R;
+
+	const uint sampleCount = 1024u;
+	float totalWeight = 0;
+	vec3 prefilteredColor = vec3(0);
+	for (uint i = 0u; i < sampleCount; i++) {
+		vec2 Xi = hammersley(i, sampleCount);
+		vec3 H = importanceSampleGGX(Xi, N, roughness);
+		vec3 L = normalize(2.f * dot(V, H) * H - V);
+
+		float NdotL = max(dot(N, L), 0.f);
+		if (NdotL > 0) {
+			prefilteredColor += texture(environmentMap, L).rgb * NdotL;
+			totalWeight += NdotL;
+		}
+	}
+
+	prefilteredColor = prefilteredColor / totalWeight;
+	fragColor = vec4(prefilteredColor, 1.f);
+}