part of DefaultRenderer_OIT_writePixel.glsl from G3D

writePixel.glsl

// colorData[0] - accum (Ar, Ag, Ab, Aa)
// colorData[2] - modulate (Br, Bg, Bb, D^2)
// colorData[3] - refraction (deltax, deltay)
void writePixel (vec3 premultipliedReflectionAndEmission, float coverage, vec3 transmissionCoefficient) {
/*
 ,
 float       collimation,
 float       etaRatio,
 vec3        csPosition,
 vec3        csNormal) {
 */

    vec3 color = premultipliedReflectionAndEmission * coverage;

    // Perform this operation before modifying the coverage to account for transmission
    colorData[2].rgb = coverage * (vec3(1.0) - transmissionCoefficient);

    /* Modulate the net coverage for composition by the transmission. This does not affect the color channels of the
     transparent surface because the caller's BSDF model should have already taken into account if transmission modulates
     reflection. See:

     McGuire and Enderton, Colored Stochastic Shadow Maps, ACM I3D, February 2011
     http://graphics.cs.williams.edu/papers/CSSM/

     for a full explanation and derivation.*/
    coverage *= 1.0 - (transmissionCoefficient.r + transmissionCoefficient.g + transmissionCoefficient.b) * (1.0 / 3.0);

    // Alternative weighting functions:
    //float tmp = 2.0 * max(1.0 + csPosition.z / 200.0, 0.0); tmp *= tmp * 1e3;

    // Looks better on clouds
    float tmp = 1.0 - gl_FragCoord.z * 0.99;
    tmp *= tmp * tmp * 1e4;
    tmp = clamp(tmp, 1e-3, 1.0);

    /*
     If you're running out of compositing range and overflowing to inf, multiply the upper bound (3e2) by a small
     constant. Note that R11G11B10F has no inf and maps all floating point specials to NaN, so you won't actually
     see inf in the frame buffer.
     */

    // Weight function tuned for the general case
    float w = clamp(coverage * tmp, 1e-3, 1.5e2);


    // another function for weight
//    float tmp = (coverage * 8.0 + 0.01) * (-gl_FragCoord.z * 0.95 + 1.0);
//    float w    = clamp(tmp * tmp * tmp * 1e3, 1e-2, 3e2);

    colorData[0] = vec4(color, coverage) * w;
    }