I ran into a possibly related issue, drawing a bunch of alphablended PNG images:
Initially, everything draws perfectly... Then if I unload every single one of my images, flushmem, etc. , change to a different screenmode and reload all images, one of them gets draws weird: the top of the image that should be alpha-blended into the background gets drawn as a straight, solid light-gray line.
(The actual sprite itself is all darkish-brown, drawn on a dark brown background. No gray present in either foreground or background. No rotation or scaling. Plain vanilla non-interlaced PNG image with alpha.)
Similar alpha gradients on the sides and bottom of the image are blended just fine.
Luckily I figured out an alternative system and I no longer need the sprite in question, but it was still a very weird issue to run into.
Initially, everything draws perfectly... Then if I unload every single one of my images, flushmem, etc. , change to a different screenmode and reload all images, one of them gets draws weird: the top of the image that should be alpha-blended into the background gets drawn as a straight, solid light-gray line.
(The actual sprite itself is all darkish-brown, drawn on a dark brown background. No gray present in either foreground or background. No rotation or scaling. Plain vanilla non-interlaced PNG image with alpha.)
Similar alpha gradients on the sides and bottom of the image are blended just fine.
Luckily I figured out an alternative system and I no longer need the sprite in question, but it was still a very weird issue to run into.