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https://github.com/QB64-Phoenix-Edition/QB64pe.git
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60 lines
3.1 KiB
Plaintext
60 lines
3.1 KiB
Plaintext
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The {{KW|CLS}} statement clears the current write page.
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{{PageSyntax}}
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::: '''CLS''' [{{Parameter|method%}}] [, {{Parameter|BGcolor&}}]
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{{Parameters}}
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* {{Parameter|method%}} specifies which parts of the page to clear, and can have one of the following values:
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** CLS - clears the active graphics or text viewport or the entire text screen and refreshes bottom function [[KEY LIST|KEY ON]] line.
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** CLS 0 - Clears the entire page of text and graphics. Print cursor is moved to row 1 at column 1.
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** CLS 1 - Clears only the graphics view port. Has no effect for text mode.
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** 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.
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* The {{Parameter|BGcolor&}} specifies the color attribute or palette index to use when clearing the screen in '''QB64 only'''.
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''Usage:''
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** In legacy [[SCREEN]] modes {{Parameter|BGcolor&}} specifies the color attribute of the background.
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** For 32-bit graphics mode, {{Parameter|BGcolor&}} specifies the [[_RGB]] or [[_RGBA]] color to use.
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* '''32 bit screen surface backgrounds(black) have zero [[_ALPHA]] so that they are transparent when placed over other surfaces.'''
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: Use [[CLS]] or [[_DONTBLEND]] to make a new surface background [[_ALPHA]] 255 or opague.
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** If not specified, {{Parameter|BGcolor&}} is assumed to be the current background color. 32 bit backgrounds will change to opaque!
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** If {{Parameter|BGColor&}} is not a valid attribute, an [[ERROR Codes|illegal function call]] error will occur!
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* Use [[_PRINTMODE]] to allow the background colors to be visible through the text or the text background.
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''Example 1:'' Printing black text on a white background in QB64.
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{{CodeStart}} '' ''
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{{Cl|SCREEN}} 12
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{{Cl|CLS}} , 15
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{{Cl|_PRINTMODE }} _KEEPBACKGROUND 'keeps the text background visible
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{{Cl|COLOR}} 0: {{Cl|PRINT}} "This is black text on a white background!"
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K$ = {{Cl|INPUT$}}(1
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{{CodeEnd}}
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:''Explanation:'' [[_PRINTMODE]] can be used with [[PRINT]] or [[_PRINTSTRING]] to make the text or the text background transparent.
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''Example 2:'' You don't need to do anything special to use a .PNG image with alpha/transparency. Here's a simple example:
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{{CodeStart}} '' ''
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{{Cl|SCREEN}} {{Cl|_NEWIMAGE}}(640, 480, 32)
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{{Cl|CLS}} , {{Cl|_RGB}}(0, 255, 0)
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i = {{Cl|_LOADIMAGE}}('''"QB64.PNG"''') 'see note below examples to get the image
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{{Cl|_PUTIMAGE}} (0, 0), i ' places image at upper left corner of window w/o stretching it
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'' ''
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{{CodeEnd}} '' ''
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: ''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]].
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<center>''Note:'' The ''QB64.PNG'' Bee image used can be copied from the top of the [http://www.qb64.net/forum/index.php Main Forum Page]</center>
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{{PageSeeAlso}}
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* [[SCREEN]]
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* [[_RGB]], [[_RGBA]]
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* [[VIEW PRINT]], [[VIEW]]
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* [[_CLEARCOLOR]]
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{{PageNavigation}}
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