Sdl_Swsurface Alpha Problem

[PokeParadox]

Well hi GP32X collective,

I am having a blending problem in SDL. When I render a HW surface everything is fine, I can set the alpha of the surface and render it and it is transparent according to the alpha.
I try and do this for a SW surface and it is either there or not...

I need the SW support to support the gradual PerPixelAlpha of png but I also need to be able to fade the surface in general and rotate and scale...

Anyone got any suggestions in general as to what may be wrong... I can obviously post code samples but the code is the Image class from the Penjin repo

As usual, any help and suggestions is greatly appreciated!

 

[mindlord]

SDL's alpha support is weird. When rendering a surface to another surface, alpha is not blended or combined the way you'd expect. It uses the alpha channel of the destination surface only. If you have a sprite with an alpha channel and draw it onto a surface that has an alpha channel too, SDL ignores the alpha channel of the sprite completely. What's worse is if the destination surface is 100% transparent, so is your sprite. I had to write a custom blitting routine in software to achieve the correct results, and it was pretty darned slow.