{{DISPLAYTITLE:_SETALPHA}}{{DISPLAYTITLE:}}
The [[_SETALPHA]] statement sets the alpha channel transparency level of some or all of the pixels of an image.


{{PageSyntax}}
: [[_SETALPHA]] {{Parameter|alpha&}}[, {{Parameter|color1&}}][ [[TO]] {{Parameter|colour2&}}] [, {{Parameter|imageHandle&}}]


{{Parameters}}
* {{Parameter|alpha&}} is the new alpha level to set, ranging from 0 (transparent) to 255 (opaque).
* {{Parameter|color1&}} designates the 32-bit [[LONG]] color value or range of color values {{Parameter|color1&}} TO {{Parameter|colour2&}} to set the transparency. 
* If no color value or range of colors is given, the entire image's alpha is changed, including any [[_CLEARCOLOR]] settings.
* If {{Parameter|imageHandle&}} is omitted, it is assumed to be the current write page or [[_DEST|destination]] image.


{{PageDescription}}
* In the first syntax, the alpha level of all pixels is set to {{Parameter|alpha&}}.
* In the second syntax, the alpha level of all pixels matching the color {{Parameter|color1&}} is set to {{Parameter|alpha&}}.
* In the third syntax, the alpha level of all pixels with red, green, blue and alpha channels in the range [{{Parameter|color1&}} TO {{Parameter|color2&}}] are set.
* The [[_ALPHA]] setting makes a 32-bit color transparent, opaque or something in between. Zero is clear and 255 totally blocks underlying images. Use it to see through backgrounds or image colors.
* If {{Parameter|alpha&}} is outside that range, an [[ERROR Codes|illegal function call]] error will occur.
* If the image specified by {{Parameter|imageHandle&}} uses a palette, an [[ERROR Codes|invalid handle]] error will occur.
* If {{Parameter|imageHandle&}} is an invalid handle, an [[ERROR Codes|illegal function call]] error will occur.
* '''NOTE: 32-bit [[_NEWIMAGE]] screen page backgrounds are transparent black or [[_ALPHA]] 0. Use [[_DONTBLEND]] or [[CLS]] for opaque.'''


{{PageExamples}}
''Example:'' Using a _SETALPHA color range to fade an image in and out while not affecting the transparent white background.
{{CodeStart}} '' ''
main = {{Cl|_NEWIMAGE}}(640, 480, 32) 
{{Cl|SCREEN}} main
{{Cl|_SCREENMOVE}} {{Cl|_SCREENMOVE|_MIDDLE}}

Image1& = {{Cl|_LOADIMAGE}}("qb64_trans.png") '<<< PNG file with white background to hide
{{Cl|_SOURCE}} Image1&
clr~& = {{Cl|POINT}}(0, 0) 'find background color of image
{{Cl|_CLEARCOLOR}} clr~&, Image1& 'set background color as transparent

topclr~& = clr~& - {{Cl|_RGBA}}(1, 1, 1, 0)  'get topmost color range just below full white
{{Cl|_DEST}} main

a& = 0
d = 1
DO
  {{Cl|_LIMIT}} 10 'regulate speed of fade in and out
  {{Cl|CLS}} ', {{Cl|_RGB}}(255, 0, 0)
  a& = a& + d
  {{Cl|IF...THEN|IF}} a& = 255 {{Cl|THEN}} d = -d
  {{Cl|_SETALPHA}} a&, 0 {{Cl|TO}} topclr~&, Image1& 'affects all colors below bright white
  {{Cl|_PUTIMAGE}} (0, 342), Image1& 
  {{Cl|LOCATE}} 1, 1: {{Cl|PRINT}} "Alpha: "; a&
  {{Cl|_DISPLAY}}
{{Cl|LOOP}} {{Cl|UNTIL}} a& = 0 '' ''
{{CodeEnd}}
: ''Explanation:'' The [[POINT]] value minus [[_RGBA]](1, 1, 1, 0) subtracts a small amount from the bright white color value so that the top [[_SETALPHA]] color range will not affect the [[_CLEARCOLOR]] transparency of the bright white PNG background. [http://www.qb64.net/qb64_trans.png qb64_trans.png].


{{PageSeeAlso}}
* [[_ALPHA]], [[_ALPHA32]]
* [[_RGBA]], [[_RGBA32]]
* [[_CLEARCOLOR]]
* [[_CLEARCOLOR (function)]]
* [[_BLEND]], [[_DONTBLEND]] 
* [[COLOR]], [[Images]]


{{PageNavigation}}