Premultiplied alpha

[vorg]

We should have one official way
http://webglfundamentals.org/webgl/lessons/webgl-and-alpha.html

Related issue in Plask
deanm/plask#37

Similar issue in ThreeJS
mrdoob/three.js#1074

[deanm]

From my experience I can tell you to use premultiplied alpha, it is almost always better and I believe the browsers will be usually using it internally anyway. So just pixelStorei(UNPACK_PREMULTIPLY_ALPHA_WEBGL, 1)

You can see the WebKit/Blink code here, an HTMLCanvas element is premultiplied, but apparently video tag frames are not.

https://chromium.googlesource.com/chromium/blink/+/8ae4164b18cdd43aeb23f4046b95006243a12474/Source/platform/graphics/gpu/WebGLImageConversion.cpp#1577