Difference between revisions of "ALPHA"

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{{PageSeeAlso}}
 
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* {{KW|_ALPHA32}}
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* {{KW|_ALPHA32}}, {{KW|_SETALPHA}}
 
* {{KW|_RED}}, {{KW|_GREEN}}, {{KW|_BLUE}}
 
* {{KW|_RED}}, {{KW|_GREEN}}, {{KW|_BLUE}}
 
* {{KW|_RED32}}, {{KW|_GREEN32}}. {{KW|_BLUE32}}
 
* {{KW|_RED32}}, {{KW|_GREEN32}}. {{KW|_BLUE32}}

Revision as of 02:25, 14 August 2010

The _ALPHA function returns the alpha channel level of a color value.


Syntax

result& = _ALPHA(colour& [, imageHandle&])


Description

  • If imageHandle& is omitted, it is assumed to be the current write page.
  • If the image specified by imageHandle& uses a palette, c& is the palette index of the color value used to retrieve the alpha level.
    • Color values that match the clear color set by _CLEARCOLOR have an alpha level of 0 (zero).
    • Color values that don't match the clear color have an alpha level of 255.
    • If colour& value is outside of the range 0 to 255, an Illegal function call error will occur.
  • If the image specified by imageHandle& does not use a palette, colour& is the color value used to retrieve the alpha level.
  • If imageHandle& is an invalid handle, an Illegal function call error will occur.
  • _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 (B8:G8:R8:A8). Using these in your code (opposed to dividing then ANDing 32-bit color values manually) makes your code easy to read too.


See also



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