ALPHA32: Difference between revisions

Revision as of 16:54, 22 January 2023

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 21: / Line 21: @@
 {{PageExamples}}
 ''Example:'' Finding the alpha transparency level in a 32 bit screen using an [[_RGBA]]  [[_UNSIGNED]] [[LONG]] color value.
-{{CodeStart}} '' ''
+{{CodeStart}}
 {{Cl|SCREEN}} {{Cl|_NEWIMAGE}}(640, 480, 32)
@@ Line 30: / Line 30: @@
 {{Cl|PRINT}} "Alpha32:"; {{Cl|_ALPHA32}}(clr~&)
-{{Cl|END}} '' ''
+{{Cl|END}}
 {{CodeEnd}}
 {{OutputStart}}{{text|Color: 3237937407|#FFFFFF}}