Difference between revisions of "ALPHA"

From QB64 Wiki
Jump to navigation Jump to search
imported>Clippy
m
imported>Clippy
m
Line 24: Line 24:
 
{{Cl|PRINT}} {{Cl|_ALPHA}}(x) '' ''
 
{{Cl|PRINT}} {{Cl|_ALPHA}}(x) '' ''
 
{{CodeEnd}}
 
{{CodeEnd}}
: ''Explanation:'' You need to set the ALPHA value using [[CLS]] to make the black background opaque!
+
: ''Explanation:'' You need to set the ALPHA value to 255 using [[CLS]] to make the black background opaque!
  
  

Revision as of 07:39, 17 June 2011

The _ALPHA function returns the alpha channel transparency level of a color value used on a screen page or image.


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, colour& is the palette index of the color value used.
    • 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 also.


Example: Finding the transparency of a 32 bit screen mode's background.

SCREEN _NEWIMAGE(640, 480, 32) 'CLS 'uncomment CLS to see how it changes the ALPHA value! x = POINT(1, 1) PRINT _ALPHA(x)

Explanation: You need to set the ALPHA value to 255 using CLS to make the black background opaque!


See also



Navigation:
Keyword Reference - Alphabetical
Keyword Reference - By Usage
Main Wiki Page