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_CLEARCOLOR

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Samuel Gomes edited this page Nov 8, 2022 · 1 revision

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&]

Parameter(s)

  • 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 ERROR Codes 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.

Description

  • If Dest_Handle& is an invalid handle, then an ERROR Codes 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(s)

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

SCREEN 13
img& = _LOADIMAGE("qb64_trans.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

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$ <> ""

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("qb64_trans.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 background was not put onto a separate page, _SETALPHA would display it also.

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