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#version 330 core
in vec2 vTex;
out vec4 FragColor;
uniform sampler2D occlusionTex;
uniform vec2 lightScreenPos; // in [0,1]
uniform vec3 sunColor;
uniform float sunIntensity;
uniform float globalIntensity;
uniform int samples;
uniform float density;
uniform float weight;
uniform float decay;
void main()
{
vec2 texCoord = vTex;
// vector from current pixel to light
vec2 delta = lightScreenPos - texCoord;
float dist = length(delta);
vec2 stepv = delta * (1.0 / float(samples)) * density;
vec3 illumination = vec3(0.0);
float illumDecay = 1.0;
vec2 coord = texCoord;
for (int i = 0; i < samples; ++i)
{
coord += stepv;
vec3 sample = texture(occlusionTex, coord).rgb;
// occlusion tex stores white where geometry present
float occ = sample.r;
illumination += occ * illumDecay * weight;
illumDecay *= decay;
}
vec3 result = illumination * sunColor * sunIntensity * globalIntensity;
// tone-map / clamp to avoid extreme brightness
result = clamp(result, vec3(0.0), vec3(1.0));
// use luminance as alpha so we can composite less aggressively
float lum = dot(result, vec3(0.299, 0.587, 0.114));
float alpha = clamp(lum, 0.0, 1.0);
FragColor = vec4(result, alpha);
}
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