From e5410e23a2c92cacbd7060f7371f4c6f3acd18f8 Mon Sep 17 00:00:00 2001
From: Vincent Lejeune <vljn@ovi.com>
Date: Sun, 11 May 2014 18:00:30 +0200
Subject: [PATCH] Use Alchemy SSAO

---
 data/shaders/ssao.frag | 79 ++++++++++++++++++++++--------------------
 1 file changed, 42 insertions(+), 37 deletions(-)

diff --git a/data/shaders/ssao.frag b/data/shaders/ssao.frag
index 110b0b51d..6179cb46c 100644
--- a/data/shaders/ssao.frag
+++ b/data/shaders/ssao.frag
@@ -1,3 +1,5 @@
+// From paper http://graphics.cs.williams.edu/papers/AlchemyHPG11/
+
 uniform sampler2D ntex;
 uniform sampler2D dtex;
 uniform sampler2D noise_texture;
@@ -22,57 +24,60 @@ layout (std140) uniform MatrixesData
 in vec2 uv;
 out float AO;
 
-const float strengh = 5.;
-const float radius = 1.f;
+const float sigma = 1.;
+const float beta = 0.0001;
+const float epsilon = .00001;
+const float radius = .1;
+const float k = 1.;
 
 #define SAMPLES 16
 
-const float invSamples = strengh / SAMPLES;
-
-vec3 rand(vec2 co)
-{
-	float noiseX = clamp(fract(sin(dot(co ,vec2(12.9898,78.233))) * 43758.5453),0.0,1.0)*2.0-1.0;
-	float noiseY = clamp(fract(sin(dot(co ,vec2(12.9898,78.233)*2.0)) * 43758.5453),0.0,1.0)*2.0-1.0;
-   return vec3(noiseX, noiseY, length(texture(noise_texture, co * pow(3.14159265359, 2.)).xyz));
-}
+const float invSamples = 1. / SAMPLES;
 
 vec3 DecodeNormal(vec2 n);
 vec4 getPosFromUVDepth(vec3 uvDepth, mat4 InverseProjectionMatrix);
 
+vec3 rand(vec2 co)
+{
+    float noiseX = clamp(fract(sin(dot(co ,vec2(12.9898,78.233))) * 43758.5453),0.0,1.0)*2.0-1.0;
+    float noiseY = clamp(fract(sin(dot(co ,vec2(12.9898,78.233)*2.0)) * 43758.5453),0.0,1.0)*2.0-1.0;
+    return vec3(noiseX, noiseY, length(texture(noise_texture, co * pow(3.14159265359, 2.)).xyz));
+}
+
 void main(void)
 {
-	vec4 cur = texture(ntex, uv);
-	float curdepth = texture(dtex, uv).x;
+    vec4 cur = texture(ntex, uv);
+    float curdepth = texture(dtex, uv).x;
     vec4 FragPos = getPosFromUVDepth(vec3(uv, curdepth), InverseProjectionMatrix);
+	if (FragPos.z < 0.) discard;
 
-	// get the normal of current fragment
-	vec3 norm = normalize(DecodeNormal(2. * texture(ntex, uv).xy - 1.));
-	// Workaround for nvidia and skyboxes
-	float len = dot(vec3(1.0), abs(cur.xyz));
-	if (len < 0.2 || curdepth > 0.9955) discard;
-	// Make a tangent as random as possible
-	vec3 randvect = rand(uv);
-	vec3 tangent = normalize(cross(norm, randvect));
-	vec3 bitangent = cross(norm, tangent);
+    // get the normal of current fragment
+    vec3 norm = normalize(DecodeNormal(2. * texture(ntex, uv).xy - 1.));
+    // Workaround for nvidia and skyboxes
+    float len = dot(vec3(1.0), abs(cur.xyz));
+    if (len < 0.2 || curdepth > 0.9955) discard;
 
-	float bl = 0.0;
+    float randAngle = rand(uv).x;
+    vec2 Xaxis = vec2(cos(randAngle), sin(randAngle));
+    Xaxis = normalize(Xaxis);
+    vec2 Yaxis = vec2(sin(randAngle), -cos(randAngle));
+    Yaxis = normalize(Yaxis);
 
-	for(int i = 0; i < SAMPLES; ++i) {
-		vec3 sampleDir = samplePoints[i].x * tangent + samplePoints[i].y * bitangent + samplePoints[i].z * norm;
-		sampleDir *= samplePoints[i].w;
-		vec4 samplePos = FragPos + radius * vec4(sampleDir, 0.0);
-		vec4 sampleProj = ProjectionMatrix * samplePos;
-		sampleProj /= sampleProj.w;
+    float bl = 0.0;
 
-		bool isInsideTexture = (sampleProj.x > -1.) && (sampleProj.x < 1.) && (sampleProj.y > -1.) && (sampleProj.y < 1.);
-		// get the depth of the occluder fragment
-		float occluderFragmentDepth = texture(dtex, (sampleProj.xy * 0.5) + 0.5).x;
-		// Position of the occluder fragment in worldSpace
-		vec4 occluderPos = getPosFromUVDepth(vec3((sampleProj.xy * 0.5) + 0.5, occluderFragmentDepth), InverseProjectionMatrix);
+    for(int i = 0; i < SAMPLES; ++i) {
+        vec2 occluder_uv = samplePoints[i].x * Xaxis + samplePoints[i].y * Yaxis;
+        occluder_uv *= samplePoints[i].w * radius;
+        occluder_uv += uv;
 
-		bool isOccluded = isInsideTexture && (sampleProj.z > (2. * occluderFragmentDepth - 1.0)) && (distance(FragPos, occluderPos) < radius);
-		bl += isOccluded ? samplePoints[i].z * smoothstep(5 * radius, 0, distance(samplePos, FragPos)) : 0.;
-	}
+        if (occluder_uv.x < 0. || occluder_uv.x > 1. || occluder_uv.y < 0. || occluder_uv.y > 1.) continue;
 
-	AO = max(1.0 - bl * invSamples, 0.);
+        float occluderFragmentDepth = texture(dtex, occluder_uv).x;
+        vec4 OccluderPos = getPosFromUVDepth(vec3(occluder_uv, occluderFragmentDepth), InverseProjectionMatrix);
+
+        vec3 vi = (OccluderPos - FragPos).xyz;
+        bl += max(0, dot(vi, norm) - FragPos.z * beta) / (dot(vi, vi) + epsilon);
+    }
+
+    AO = max(pow(1.0 - 2. * sigma * bl * invSamples, k), 0.);
 }