alpha transparency

[mrglennjones]

when displaying png files with an alpha transparency channel, the transparency isnt shown, instead its, just solid back pixels.

this would be useful for over laying graphics on top of each over

[Gadgetoid]

I think we've got appetite to add alpha blending, but it will be a fair amount of work and will have a significant impact on performance when you use it.

Things like the "fade in and out" mentioned in #48 would work, but an alpha blend requires reading pixels, performing (read: trying very hard to avoid floating point) maths and writing them back which is going to be slow in comparison to opaque pixels (which can be slammed into the framebuffer very quickly using optimised routines).

This is evident when turning on anti-aliasing for PicoVector, which alpha blends the edge pixels using a specific written-just-for-vector-graphics drawing routine. You can feel the performance cost for just the edges, so imagine doing the whole object!

[mrglennjones]

I think we've got appetite to add alpha blending, but it will be a fair amount of work and will have a significant impact on performance when you use it.

Things like the "fade in and out" mentioned in #48 would work, but an alpha blend requires reading pixels, performing (read: trying very hard to avoid floating point) maths and writing them back which is going to be slow in comparison to opaque pixels (which can be slammed into the framebuffer very quickly using optimised routines).

This is evident when turning on anti-aliasing for PicoVector, which alpha blends the edge pixels using a specific written-just-for-vector-graphics drawing routine. You can feel the performance cost for just the edges, so imagine doing the whole object!

yes i figured it could be a bit of a processor hogger, thought id mentioned anyway, just incase you can perform some magic :)