Tuple of four small ints used to fill a BLENDFUNCTION struct Each int must fit in a byte (0-255).

Win32 API References

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[0] int : BlendOp

Only defined value is AC_SRC_OVER (0)

[1] int : BlendFlags

None currently defined, must be 0

[2] int : SourceConstantAlpha

Transparency to be applied to entire source. (255 is opaque)

[3] int : AlphaFormat

Only defined flag is AC_SRC_ALPHA, used when src bitmap contains per-pixel alpha