Improve DoF

[dmnsgn]

• optimisation discard if blur radius is negligible

if (centerSize < 0.05) color = texture2D(uTexture, texCoord).rgb;

• separable dof start/end + falloff

if (manualdof) {
    float a = centerDepth - uFocalLength; // focal plane
    float b = (a - fdofstart) / fdofdist; // far DoF
    float c = (-a - ndofstart) / ndofdist; // near Dof
    blur = (a > 0.0) ? b : c;
}

• use sensor size for CoC
• parametrize MAX_BLUR. Is it bokeh size?
• multipass: CoC + downscaled + combine
• Implement Circular Seperable Depth of Field: https://github.com/kecho/CircularDofFilterGenerator/blob/master/circulardof.pdf or Practical Gather-based Bokeh Depth of Field (from GPU Zen: Advanced Rendering Techniques)