Alpha Values Per Pixel

[This is preliminary documentation and subject to change.]

Alpha values per pixel are only supported for 32-bit-per-pixel BI_RGB. This formula is defined as :

typedef struct {
    BYTE   Blue;
    BYTE   Green;
    BYTE    Red;
    BYTE    Alpha;
};
 

This is represented in memory as:

31:24  

23:16  

15:08  

07:00

Alpha  

Red  

Green  

Blue

Global Alpha Blending Settings

Bitmaps may also be displayed with a transparency factor applied to the entire bitmap. Any bitmap format can be displayed with a global constant alpha value by setting SourceConstantAlpha in the BLENDFUNCTION structure. The global constant alpha value has 256 levels of transparency, from 0 (entire bitmap is completely transparent) to 255 (entire bitmap is completely opaque). The global constant alpha value is combined with the per-pixel alpha value.