_ALPHA32 - QB64Official/qb64 GitHub Wiki

The _ALPHA32 function returns the alpha transparency level of a 32 bit color value.

Syntax

alpha& = _ALPHA32(color32~&)**

Parameter(s)

  • color32& is the _UNSIGNED LONG 32 bit color value used to retrieve the alpha level.
    • Color values that are set as a _CLEARCOLOR always have an alpha level of 0 (transparent).
    • _SETALPHA can set any alpha level from 0 (or fully transparent) to 255 (or opaque).
    • Normal color values that are set by _RGB or _RGB32 always have an alpha level of 255 (opaque).

Description

  • In 4-bit (16 colors) or 8-bit (256 colors) palette screens the function will return 0.
  • _RED32, _GREEN32, _BLUE32 and _ALPHA32 are all equivalent to _RED, _GREEN, _BLUE and _ALPHA but they are highly optimized and only accept a 32-bit color (RGBA) value. Using these in your code (opposed to dividing then ANDing 32-bit color values) makes code easy to read.
  • NOTE: 32 bit _NEWIMAGE screen page backgrounds are transparent black or _ALPHA 0. Use _DONTBLEND or CLS for opaque!

Example(s)

Finding the alpha transparency level in a 32 bit screen using an _RGBA _UNSIGNED LONG color value.


SCREEN _NEWIMAGE(640, 480, 32)

clr~& = _RGBA(255, 0, 255, 192)
PRINT "Color:"; clr~&

COLOR clr~&
PRINT "Alpha32:"; _ALPHA32(clr~&)

END 



Color: 3237937407
Alpha32: 192

Notes: The color value is equivalent to &H &HC0FF00FF where &HC0 equals 192. _RGB alphas are always &HFF(255).

See Also