blend_premul_alpha render mode

Question

What's the exact blending operation that blend_premul_alpha shader mode applies to pixels?

Jurisprudent

Answer 1

premul_alpha is premultiplied alpha.

When the alpha component is equal to 0, it behaves as an additive blend mode. When the alpha component is equal to 255, it behaves as a mix blend mode. Anything between will be a mix between an additive and a mix blend mode.

You can read more about premultiplied alpha here: https://limnu.com/premultiplied-alpha-primer-artists/

Halifax

Answer 2

So it's a blending mode used to "properly" draw textures that are already premultiplied? Equivalent to opengl's (GL_ONE, GL_ONE_MINUS_SRC_ALPHA)?

Jurisprudent

Answer 3

@xyz said: So it's a blending mode used to "properly" draw textures that are already premultiplied? Equivalent to opengl's (GL_ONE, GL_ONE_MINUS_SRC_ALPHA)?

Yes :)

Halifax