dinasset wrote:
b) if the base layer (the one to which other layers are then added using one of the mentioned modes) has no alpha channel, then the effect is actually the same as "normal"
c) if the base layer has alpha channel, then:
c1 - "replace" acts apparently like "normal" (but I suspect there are differences)
'Replace' mode uses the alpha channel of the top layer to produce the resulting alpha regardless of the value (or even presence) of the alpha below it. Note that the
resulting alpha then gets blended with the alpha of the lower layer based upon the Opacity setting.
dinasset wrote:
c2 - "erase" removes the (equivalent color?) pixels from the base layer
c3 - "anti-erase" maybe does the opposite of "erase" but I'm not sure
For both 'erase' and 'anti-erase' modes, the RGB channels of the top layer are ignored.
'Erase' mode subtracts the alpha channel of the top layer from the alpha channel of the bottom to produce the resulting alpha. Again, the resulting alpha then gets blended with the alpha of the lower layer based upon the Opacity setting.
'Anti-erase' mode adds the alpha channel of the top layer to the alpha channel of the bottom to produce the resulting alpha. And then the resulting alpha gets blended with the alpha of the lower layer based upon the Opacity setting.