Added shaders for PBR IBL pre-filtered environment map generation [skip ci]

data/shaders/pbribl/filtercube.vert

@@ -0,0 +1,19 @@
+#version 450
+
+layout (location = 0) in vec3 inPos;
+
+layout(push_constant) uniform PushConsts {
+	layout (offset = 0) mat4 mvp;
+} pushConsts;
+
+layout (location = 0) out vec3 outUVW;
+
+out gl_PerVertex {
+	vec4 gl_Position;
+};
+
+void main() 
+{
+	outUVW = inPos;
+	gl_Position = pushConsts.mvp * vec4(inPos.xyz, 1.0);
+}

data/shaders/pbribl/prefilterenvmap.frag

@@ -0,0 +1,90 @@
+#version 450
+
+layout (location = 0) in vec3 inPos;
+layout (location = 0) out vec4 outColor;
+
+layout (binding = 0) uniform samplerCube samplerEnv;
+
+layout(push_constant) uniform PushConsts {
+	layout (offset = 64) float roughness;
+	layout (offset = 68) uint numSamples;
+} pushConsts;
+
+const float PI = 3.1415926536;
+
+// Based omn http://byteblacksmith.com/improvements-to-the-canonical-one-liner-glsl-rand-for-opengl-es-2-0/
+float random(vec2 co)
+{
+	float a = 12.9898;
+	float b = 78.233;
+	float c = 43758.5453;
+	float dt= dot(co.xy ,vec2(a,b));
+	float sn= mod(dt,3.14);
+	return fract(sin(sn) * c);
+}
+
+vec2 hammersley2d(uint i, uint N) 
+{
+	// Radical inverse based on http://holger.dammertz.org/stuff/notes_HammersleyOnHemisphere.html
+	uint bits = (i << 16u) | (i >> 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);
+	float rdi = float(bits) * 2.3283064365386963e-10;
+	return vec2(float(i) /float(N), rdi);
+}
+
+// Based on http://blog.selfshadow.com/publications/s2013-shading-course/karis/s2013_pbs_epic_slides.pdf
+vec3 importanceSample_GGX(vec2 Xi, float roughness, vec3 normal) 
+{
+	// Maps a 2D point to a hemisphere with spread based on roughness
+	float alpha = roughness * roughness;
+	float phi = 2.0 * PI * Xi.x + random(normal.xz) * 0.1;
+	float cosTheta = sqrt((1.0 - Xi.y) / (1.0 + (alpha*alpha - 1.0) * Xi.y));
+	float sinTheta = sqrt(1.0 - cosTheta * cosTheta);
+	vec3 H = vec3(sinTheta * cos(phi), sinTheta * sin(phi), cosTheta);
+
+	// Tangent space
+	vec3 up = abs(normal.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
+	vec3 tangentX = normalize(cross(up, normal));
+	vec3 tangentY = normalize(cross(normal, tangentX));
+
+	// Convert to world Space
+	return normalize(tangentX * H.x + tangentY * H.y + normal * H.z);
+}
+
+// Normal Distribution function
+float D_GGX(float dotNH, float roughness)
+{
+	float alpha = roughness * roughness;
+	float alpha2 = alpha * alpha;
+	float denom = dotNH * dotNH * (alpha2 - 1.0) + 1.0;
+	return (alpha2)/(PI * denom*denom); 
+}
+
+vec3 prefilterEnvMap(vec3 R, float roughness)
+{
+	vec3 N = R;
+	vec3 V = R;
+	vec3 color = vec3(0.0);
+	float totalWeight = 0.0;
+	for(uint i = 0u; i < pushConsts.numSamples; i++) {
+		vec2 Xi = hammersley2d(i, pushConsts.numSamples);
+		vec3 H = importanceSample_GGX(Xi, roughness, N);
+		vec3 L = 2.0 * dot(V, H) * H - V;
+		float dotNL = clamp(dot(N, L), 0.0, 1.0);
+		if(dotNL > 0.0) {
+			color += texture(samplerEnv, L).rgb * dotNL;
+			totalWeight += dotNL;
+		}
+	}
+	return (color / totalWeight);
+}
+
+
+void main()
+{		
+	vec3 N = normalize(inPos);
+	outColor = vec4(prefilterEnvMap(N, pushConsts.roughness), 1.0);
+}