_CLEARCOLOR - QB64 Wiki

_CLEARCOLOR

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The _CLEARCOLOR statement sets a specific color to be treated as transparent when an image is later put (via _PUTIMAGE) onto another image.


Syntax:

_CLEARCOLOR {color&|_NONE}[, Dest_Handle&]


Parameters:

  • In color modes using a palette, color& is the palette index of the new transparent color value or _NONE designates no clear colors.
  • If color& is not a valid palette index, an illegal function call error will occur.
  • In 32-bit color modes, color& is the _LONG color value of the new transparent color.
  • If Dest_Handle& is omitted, the destination is assumed to be the current write page. Zero can designate the current program screen.


Usage:

  • If Dest_Handle& is an invalid handle, then an invalid handle error is returned. Check for bad handle values of -1 first!
  • In 32-bit color modes, it simply sets the Alpha to 0 for all pixels matching the specified color.
  • In the second syntax, transparency is disabled for color modes using a palette.
  • Note: _SETALPHA can affect any _CLEARCOLOR alpha setting within the color range set!
  • NOTE: 32 bit _NEWIMAGE screen page backgrounds are transparent black or _ALPHA 0. Use _DONTBLEND or CLS for opaque!


Example 1: Using _CLEARCOLOR to "mask" the background color of an image.

SCREEN 13 img& = _LOADIMAGE("QB64bee.png") _PUTIMAGE , img&, 0 'place actual image with background K$ = INPUT$(1) CLS , _RGB(255, 0, 0) 'clear screen with red background _CLEARCOLOR _RGB(255, 255, 255), img& _PUTIMAGE , img&, 0 'place image without white background PRINT _CLEARCOLOR(img&) 'displays closest clear color attribute END

Note: The QB64.PNG image can be downloaded here: QB64bee.png. Right click and Save as QB64bee.PNG.


Example 2: Using a _CLEARCOLOR transparency with images created on a _NEWIMAGE page. Does not require an image file.

SCREEN _NEWIMAGE(512, 384, 32) ' screen uses handle value CIRCLE(50, 50), 50, _RGB(128, 0, 0) ' create a red ball image PAINT(50, 50), _RGB(255, 0, 0), _RGB(128, 0, 0) redball = _NEWIMAGE(101, 101, 32) ' create a new image page _PUTIMAGE , 0, redball,(0, 0)-(101, 101) ' put screen page 0 image onto redball page _CLEARCOLOR _RGB(0, 0, 0), redball ' makes black become see-through CLS, _RGB(0, 0, 255) ' erase original ball and create a blue background DO _PUTIMAGE (RND * 512, RND * 384), redball SLEEP 1 ' one second delay LOOP UNTIL INKEY$ <> ""


Example 3: Fading an image with a _CLEARCOLOR background using a new page image to prevent _SETALPHA changes.

mainscreen = _NEWIMAGE(640, 480, 32) ' Main Screen (viewable) SCREEN mainscreen _SCREENMOVE _MIDDLE Image1& = _LOADIMAGE("QB64bee.png") '<<<<<< any image with one background color to clear IF Image1& < -1 THEN 'check loaded image handle value before using! _SOURCE Image1& clr~& = POINT(0, 0) 'get background color from image source _CLEARCOLOR clr~&, Image1& 'clear background color of loaded image NewImage1& = _NEWIMAGE(_WIDTH(Image1&), _HEIGHT(Image1&), 32) 'new image page _PUTIMAGE , Image1&, NewImage1& 'put image without background color on new page _FREEIMAGE Image1& 'free loaded image from memory END IF _DEST mainscreen: a& = 0: d = 1 DO _LIMIT 10 'regulate speed of fades CLS a& = a& + d IF a& = 255 THEN d = -d 'reverse fade _SETALPHA a&, , NewImage1& 'sets alpha level of all colors to fade image page in/out _PUTIMAGE (0, 342), NewImage1& LOCATE 1, 1: PRINT "Alpha: "; a& _DISPLAY LOOP UNTIL a& = 0 END

Note: If the _CLEARCOLOR QB64bee.png background was not put onto a separate page, _SETALPHA would display it also.


See also:



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