Missing blendmodes

[grandchild]

Some blendmodes are still unsupported:

• [ ] XOR
• [ ] Every other line
• [ ] Every other pixel
• [ ] Buffer

XOR

XOR is tricky in WebGL 1.0, which has no bitwise integer operations. There are involved algorithms which emulate xor.

• https://stackoverflow.com/questions/373262/how-do-you-implement-xor-using
• https://stackoverflow.com/questions/3543273/glsl-why-are-bitwise-operators-reserved-what-is-a-good-alternative-to-using-b#3543304

Every other *

Every other line/pixel is also not straightforward, because we need pixel-coordinate access. This code

mix(color, getSrcColor(), float(uint(dot(v_position, u_resolution-1.0)) & 1u))

(which is only valid in GLSL ES 3 / WebGl 2.0) produces different output across browsers -- and always incorrect (artifacts along the diagonal). If there's a way we could have not only 0-1-valued texture coordinates but also correct pixel/texel-coordinates, then we'd be done with these.