From ef2416493d4b639d763940d4188397e482426ffe Mon Sep 17 00:00:00 2001
From: Jonathan Olson <olsonsjc@gmail.com>
Date: Sun, 23 Feb 2014 21:10:32 -0700
Subject: [PATCH] Gamma correction, quadratic light falloff, and randomness
 improvements.

Adding gamma correction so that samples are blended linearly and then displayed for more accurate colors (adjusted colors to match current behavior). Added quadratic light falloff for realism (a light next to a colored wall will now correctly light the area more with that color). Improved random sampling to minimize banding behavior and prevent artifacts from rendering after it's been left open for a few days.
---
 webgl-path-tracing.js | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/webgl-path-tracing.js b/webgl-path-tracing.js
index 5d004dd..43c8751 100644
--- a/webgl-path-tracing.js
+++ b/webgl-path-tracing.js
@@ -30,6 +30,9 @@
 // shader strings
 ////////////////////////////////////////////////////////////////////////////////
 
+var gamma = 2.2;
+var invGamma = 1/gamma;
+
 // vertex shader for drawing a textured quad
 var renderVertexSource =
 ' attribute vec3 vertex;' +
@@ -46,6 +49,7 @@ var renderFragmentSource =
 ' uniform sampler2D texture;' +
 ' void main() {' +
 '   gl_FragColor = texture2D(texture, texCoord);' +
+'   gl_FragColor.rgb = pow( gl_FragColor.rgb*0.7, vec3( ' + invGamma + ' ) );' +
 ' }';
 
 // vertex shader for drawing a line
@@ -145,8 +149,11 @@ var normalForSphereSource =
 
 // use the fragment position for randomness
 var randomSource =
-' float random(vec3 scale, float seed) {' +
-'   return fract(sin(dot(gl_FragCoord.xyz + seed, scale)) * 43758.5453 + seed);' +
+' highp float random(highp vec3 scale, float seed) {' +
+'   highp float d = 43758.5453;' +
+'   highp float dt = dot(gl_FragCoord.xyz + seed,scale);' +
+'   highp float sn = mod(dt,3.1415926);' +
+'   return fract(sin(sn) * d);' +
 ' }';
 
 // random cosine-weighted distributed vector
@@ -208,12 +215,12 @@ var newGlossyRay =
 ' specularHighlight = pow(specularHighlight, 3.0);';
 
 var yellowBlueCornellBox =
-' if(hit.x < -0.9999) surfaceColor = vec3(0.1, 0.5, 1.0);' + // blue
-' else if(hit.x > 0.9999) surfaceColor = vec3(1.0, 0.9, 0.1);'; // yellow
+' if(hit.x < -0.9999) surfaceColor = pow(vec3(0.1, 0.5, 1.0), vec3(' + gamma + '));' + // blue
+' else if(hit.x > 0.9999) surfaceColor = pow(vec3(1.0, 0.9, 0.1), vec3(' + gamma + '));'; // yellow
 
 var redGreenCornellBox =
-' if(hit.x < -0.9999) surfaceColor = vec3(1.0, 0.3, 0.1);' + // red
-' else if(hit.x > 0.9999) surfaceColor = vec3(0.3, 1.0, 0.1);'; // green
+' if(hit.x < -0.9999) surfaceColor = pow(vec3(1.0, 0.3, 0.1), vec3(' + gamma + '));' + // red
+' else if(hit.x > 0.9999) surfaceColor = pow(vec3(0.3, 1.0, 0.1), vec3(' + gamma + '));'; // green
 
 function makeShadow(objects) {
   return '' +
@@ -261,7 +268,7 @@ function makeCalculateColor(objects) {
 
       // compute diffuse lighting contribution
 '     vec3 toLight = light - hit;' +
-'     float diffuse = max(0.0, dot(normalize(toLight), normal));' +
+'     float diffuse = max(0.0, dot(normalize(toLight), normal))/dot(toLight,toLight);' +
 
       // trace a shadow ray to the light
 '     float shadowIntensity = shadow(hit + normal * ' + epsilon + ', toLight);' +
@@ -712,7 +719,7 @@ PathTracer.prototype.update = function(matrix, timeSinceStart) {
   this.uniforms.ray01 = getEyeRay(matrix, -1, +1);
   this.uniforms.ray10 = getEyeRay(matrix, +1, -1);
   this.uniforms.ray11 = getEyeRay(matrix, +1, +1);
-  this.uniforms.timeSinceStart = timeSinceStart;
+  this.uniforms.timeSinceStart = ( timeSinceStart % 46735.275 ) / 1000; // prevent huge values being crunched in the shader
   this.uniforms.textureWeight = this.sampleCount / (this.sampleCount + 1);
 
   // set uniforms