I have a problem with UpdateLayeredWindow api. First I call it with pblend->SourceConstantAlpha=0x30 (per-pixel alpha value in hdcSrc's bitmap for all pixels =0xFF). Then I swap values (pblend->SourceConstantAlpha=0xFF, per-pixel alpha=0x30). And I see picture in both cases much differs. With SourceConstantAlpha=0x30 it looks well, like I use SetLayeredWindowAttributes. But in second case seems like in blending also takes place some white layer. This is my bug or normal ULW behavior? Can I resolve it?