From QB64 Wiki
The CLS statement clears the current write page.
- CLS [method%] [, BGcolor&]
- 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.
- 32 bit screen surface backgrounds(black) have zero _ALPHA so that they are transparent when placed over other surfaces.
- 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.
- 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.