public enum RenderState.BlendMode

The alpha blending mode applied when a fragment is written.

A fragment’s color is a material’s color multiplied by its texture, in straight (not premultiplied) alpha: a material colored 0x66000000 over a white texture is black at 40%, and drawn with ALPHA over an opaque destination d it leaves 0.6 * d.

The framebuffer’s own alpha channel is not blended the way its color is. In both blending modes it accumulates coverage, alpha = source + destination * (1 - source), so a frame cleared to an opaque color stays opaque whatever is blended onto it. A backend that weights the alpha by the same factor as the color leaves 0.76 under a fragment at 40%, and where the frame is composited or read back with its alpha, what is behind the view shows through the fragment.