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CLS

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The CLS statement clears the current write page.


Syntax:

CLS [method%] [, BGcolor&]


Parameters:

  • method% specifies which parts of the page to clear, and can have one of the following values:
    • CLS    - clears the active graphics or text viewport or the entire text screen and refreshes bottom function KEY ON line.
    • CLS 0 - Clears the entire page of text and graphics. Print cursor is moved to row 1 at column 1.
    • CLS 1 - Clears only the graphics view port. Has no effect for text mode.
    • CLS 2 - Clears only the text view port. The print cursor is moved to the top row of the text view port at column 1.
  • The BGcolor& specifies the color attribute or palette index to use when clearing the screen in QB64 only.


Usage:

    • In legacy SCREEN modes BGcolor& specifies the color attribute of the background.
    • For 32-bit graphics mode, BGcolor& specifies the _RGB or _RGBA color to use.
  • 32 bit screen surface backgrounds(black) have zero _ALPHA so that they are transparent when placed over other surfaces.
Use CLS or _DONTBLEND to make a new surface background _ALPHA 255 or opague.
    • If not specified, BGcolor& is assumed to be the current background color. 32 bit backgrounds will change to opaque!
    • If BGColor& is not a valid attribute, an illegal function call error will occur!
  • Use _PRINTMODE to allow the background colors to be visible through the text or the text background.


Example 1: Printing black text on a white background in QB64.

SCREEN 12 CLS , 15 _PRINTMODE _KEEPBACKGROUND 'keeps the text background visible COLOR 0: PRINT "This is black text on a white background!" K$ = INPUT$(1

Explanation: _PRINTMODE can be used with PRINT or _PRINTSTRING to make the text or the text background transparent.


Example 2: You don't need to do anything special to use a .PNG image with alpha/transparency. Here's a simple example:

SCREEN _NEWIMAGE(640, 480, 32) CLS , _RGB(0, 255, 0) i = _LOADIMAGE("QB64.PNG") 'see note below examples to get the image _PUTIMAGE (0, 0), i ' places image at upper left corner of window w/o stretching it

Explanation: When QB64 loads a 256 color .PNG file containing a transparent color, that color will be treated as transparent when _PUTIMAGE is used to put it onto another image. So actually, you can use a 256-color .PNG file containing transparency information in a 256 color screen mode in QB64. CLS sets the _CLEARCOLOR setting using _RGB.
Note: The QB64.PNG Bee image used can be copied from the top of the Main Forum Page


See also:



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