Does anyone know if it’s possible to do a signed-add blend mode? Preferably with something <2.0 since I’m after good hardware compatibility, especially integrated intel chips from a few years back.
I’m after something along the lines of (assuming everything in the range [0,1] ):
framebuffer.rgb = (framebuffer.rgb * 2 - 1) + (fragment.rgb * 2 - 1)
Ideally the fragment alpha would be multiplied by the fragment.rgb beforehand, but I can probably hack around that if it’s not possible.
The closest I can come up with at the moment is splitting it into two passes, one with regular additive and one with Ext_blend_subtract, but obviously that’s not ideal and requires some preprocessing to split my textures up into their +ive and -ive components.
Any hints appreciated. Thanks.