ALPHA32: Difference between revisions

Latest revision as of 19:21, 24 May 2024

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

alpha& = _ALPHA32(color32~&)

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).

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: 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).

@@ Line 23: / Line 23: @@
 ''Example:'' Finding the alpha transparency level in a 32 bit screen using an [[_RGBA]]  [[_UNSIGNED]] [[LONG]] color value.
 {{CodeStart}}
-{{Cl|SCREEN}} {{Cl|_NEWIMAGE}}(640, 480, 32)
+{{Cl|SCREEN}} {{Cl|_NEWIMAGE}}({{Text|640|#F580B1}}, {{Text|480|#F580B1}}, {{Text|32|#F580B1}})
-clr~& = {{Cl|_RGBA}}(255, 0, 255, 192)
+clr~& = {{Cl|_RGBA}}({{Text|255|#F580B1}}, {{Text|0|#F580B1}}, {{Text|255|#F580B1}}, {{Text|192|#F580B1}})
-{{Cl|PRINT}} "Color:"; clr~&
+{{Cl|PRINT}} {{Text|<nowiki>"Color:"</nowiki>|#FFB100}}; clr~&
 {{Cl|COLOR}} clr~&
-{{Cl|PRINT}} "Alpha32:"; {{Cl|_ALPHA32}}(clr~&)
+{{Cl|PRINT}} {{Text|<nowiki>"Alpha32:"</nowiki>|#FFB100}}; {{Cl|_ALPHA32}}(clr~&)
 {{Cl|END}}
@@ Line 40: / Line 40: @@
 {{PageSeeAlso}}
+* [https://qb64phoenix.com/forum/showthread.php?tid=1060 Featured in our "Keyword of the Day" series]
 * [[_ALPHA]], [[_SETALPHA]]
 * [[_RGBA]], [[_RGBA32]] {{Text|(set color with alpha)}}