_ALPHA32 - QB64 Wiki

_ALPHA32

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


Syntax:

alpha& = _ALPHA32(colour32~&)


Parameters:

  • colour32& 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).


Usage:

  • In 4(16 color) or 8(256 color) bit 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: 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 hexadecimal &HC0FF00FF where &HC0 equals 192. _RGB alphas are always &HFF(255).


See also:



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