/**
* @author huwb / http://huwbowles.com/
*
* God-rays (crepuscular rays)
*
* Similar implementation to the one used by Crytek for CryEngine 2 [Sousa2008].
* Blurs a mask generated from the depth map along radial lines emanating from the light
* source. The blur repeatedly applies a blur filter of increasing support but constant
* sample count to produce a blur filter with large support.
*
* My implementation performs 3 passes, similar to the implementation from Sousa. I found
* just 6 samples per pass produced acceptible results. The blur is applied three times,
* with decreasing filter support. The result is equivalent to a single pass with
* 6*6*6 = 216 samples.
*
* References:
*
* Sousa2008 - Crysis Next Gen Effects, GDC2008, http://www.crytek.com/sites/default/files/GDC08_SousaT_CrysisEffects.ppt
*/
THREE.ShaderGodRays = {
/**
* The god-ray generation shader.
*
* First pass:
*
* The input is the depth map. I found that the output from the
* THREE.MeshDepthMaterial material was directly suitable without
* requiring any treatment whatsoever.
*
* The depth map is blurred along radial lines towards the "sun". The
* output is written to a temporary render target (I used a 1/4 sized
* target).
*
* Pass two & three:
*
* The results of the previous pass are re-blurred, each time with a
* decreased distance between samples.
*/
'godrays_generate': {
uniforms: {
tInput: {
type: "t",
value: null
},
fStepSize: {
type: "f",
value: 1.0
},
vSunPositionScreenSpace: {
type: "v2",
value: new THREE.Vector2( 0.5, 0.5 )
}
},
vertexShader: [
"varying vec2 vUv;",
"void main() {",
"vUv = uv;",
"gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",
"}"
].join("\n"),
fragmentShader: [
"#define TAPS_PER_PASS 6.0",
"varying vec2 vUv;",
"uniform sampler2D tInput;",
"uniform vec2 vSunPositionScreenSpace;",
"uniform float fStepSize;", // filter step size
"void main() {",
// delta from current pixel to "sun" position
"vec2 delta = vSunPositionScreenSpace - vUv;",
"float dist = length( delta );",
// Step vector (uv space)
"vec2 stepv = fStepSize * delta / dist;",
// Number of iterations between pixel and sun
"float iters = dist/fStepSize;",
"vec2 uv = vUv.xy;",
"float col = 0.0;",
// This breaks ANGLE in Chrome 22
// - see http://code.google.com/p/chromium/issues/detail?id=153105
/*
// Unrolling didnt do much on my hardware (ATI Mobility Radeon 3450),
// so i've just left the loop
"for ( float i = 0.0; i < TAPS_PER_PASS; i += 1.0 ) {",
// Accumulate samples, making sure we dont walk past the light source.
// The check for uv.y < 1 would not be necessary with "border" UV wrap
// mode, with a black border colour. I don't think this is currently
// exposed by three.js. As a result there might be artifacts when the
// sun is to the left, right or bottom of screen as these cases are
// not specifically handled.
"col += ( i <= iters && uv.y < 1.0 ? texture2D( tInput, uv ).r : 0.0 );",
"uv += stepv;",
"}",
*/
// Unrolling loop manually makes it work in ANGLE
"if ( 0.0 <= iters && uv.y < 1.0 ) col += texture2D( tInput, uv ).r;",
"uv += stepv;",
"if ( 1.0 <= iters && uv.y < 1.0 ) col += texture2D( tInput, uv ).r;",
"uv += stepv;",
"if ( 2.0 <= iters && uv.y < 1.0 ) col += texture2D( tInput, uv ).r;",
"uv += stepv;",
"if ( 3.0 <= iters && uv.y < 1.0 ) col += texture2D( tInput, uv ).r;",
"uv += stepv;",
"if ( 4.0 <= iters && uv.y < 1.0 ) col += texture2D( tInput, uv ).r;",
"uv += stepv;",
"if ( 5.0 <= iters && uv.y < 1.0 ) col += texture2D( tInput, uv ).r;",
"uv += stepv;",
// Should technically be dividing by 'iters', but 'TAPS_PER_PASS' smooths out
// objectionable artifacts, in particular near the sun position. The side
// effect is that the result is darker than it should be around the sun, as
// TAPS_PER_PASS is greater than the number of samples actually accumulated.
// When the result is inverted (in the shader 'godrays_combine', this produces
// a slight bright spot at the position of the sun, even when it is occluded.
"gl_FragColor = vec4( col/TAPS_PER_PASS );",
"gl_FragColor.a = 1.0;",
"}"
].join("\n")
},
/**
* Additively applies god rays from texture tGodRays to a background (tColors).
* fGodRayIntensity attenuates the god rays.
*/
'godrays_combine': {
uniforms: {
tColors: {
type: "t",
value: null
},
tGodRays: {
type: "t",
value: null
},
fGodRayIntensity: {
type: "f",
value: 0.69
},
vSunPositionScreenSpace: {
type: "v2",
value: new THREE.Vector2( 0.5, 0.5 )
}
},
vertexShader: [
"varying vec2 vUv;",
"void main() {",
"vUv = uv;",
"gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",
"}"
].join("\n"),
fragmentShader: [
"varying vec2 vUv;",
"uniform sampler2D tColors;",
"uniform sampler2D tGodRays;",
"uniform vec2 vSunPositionScreenSpace;",
"uniform float fGodRayIntensity;",
"void main() {",
// Since THREE.MeshDepthMaterial renders foreground objects white and background
// objects black, the god-rays will be white streaks. Therefore value is inverted
// before being combined with tColors
"gl_FragColor = texture2D( tColors, vUv ) + fGodRayIntensity * vec4( 1.0 - texture2D( tGodRays, vUv ).r );",
"gl_FragColor.a = 1.0;",
"}"
].join("\n")
},
/**
* A dodgy sun/sky shader. Makes a bright spot at the sun location. Would be
* cheaper/faster/simpler to implement this as a simple sun sprite.
*/
'godrays_fake_sun': {
uniforms: {
vSunPositionScreenSpace: {
type: "v2",
value: new THREE.Vector2( 0.5, 0.5 )
},
fAspect: {
type: "f",
value: 1.0
},
sunColor: {
type: "c",
value: new THREE.Color( 0xffee00 )
},
bgColor: {
type: "c",
value: new THREE.Color( 0x000000 )
}
},
vertexShader: [
"varying vec2 vUv;",
"void main() {",
"vUv = uv;",
"gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",
"}"
].join("\n"),
fragmentShader: [
"varying vec2 vUv;",
"uniform vec2 vSunPositionScreenSpace;",
"uniform float fAspect;",
"uniform vec3 sunColor;",
"uniform vec3 bgColor;",
"void main() {",
"vec2 diff = vUv - vSunPositionScreenSpace;",
// Correct for aspect ratio
"diff.x *= fAspect;",
"float prop = clamp( length( diff ) / 0.5, 0.0, 1.0 );",
"prop = 0.35 * pow( 1.0 - prop, 3.0 );",
"gl_FragColor.xyz = mix( sunColor, bgColor, 1.0 - prop );",
"gl_FragColor.w = 1.0;",
"}"
].join("\n")
}
};