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40 lines
2.1 KiB
Plaintext
40 lines
2.1 KiB
Plaintext
The {{KW|_DISPLAY}} statement turns off automatic display while only displaying the screen changes when called.
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{{PageSyntax}}
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::: '''_DISPLAY''
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''Usage:''
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* '''_DISPLAY''' turns off the default [[_AUTODISPLAY]] when used. Prevents screen flickering.
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* Call _DISPLAY each time the screen graphics are to be displayed. Place call after the image has been changed.
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* Re-enable the automatic display by calling [[_AUTODISPLAY]]. If it isn't re-enabled, things may not be displayed later!
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''Examples:'' Displaying a circle bouncing around the screen.
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{{CodeStart}} '' ''
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{{Cl|SCREEN (statement)|SCREEN}} 12
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x = 21: y =31 'start position
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dx = 3: dy = 3 'number of pixel moves per loop
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{{Cl|DO}}
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{{Cl|_LIMIT}} 100 ' set to 100 frames per second
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x = x + dx: y = y + dy
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{{Cl|IF...THEN|IF}} x < 0 {{Cl|OR}} x > 640 {{Cl|THEN}} dx = -dx 'limit columns and reverse column direction each side
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{{Cl|IF...THEN|IF}} y < 0 {{Cl|OR}} y > 480 {{Cl|THEN}} dy = -dy 'limit rows and reverse row direction top or bottom
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IF px <> x OR py <> y THEN FOR d = 1 to 20: CIRCLE (px, py), d, 0: NEXT 'erase
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FOR c = 1 TO 20: {{Cl|CIRCLE}} (x, y), c, 6: NEXT 'draw new circle at new position
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px = x: py = y 'save older coordinates to erase older circle next loop
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{{Cl|_DISPLAY}} 'after new circle is set, show it
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{{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|INKEY$}} = CHR$(27) '' ''
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{{CodeEnd}}
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:''Explanation:'' The loop is set with [[_LIMIT]] to 100 frames per second to limit CPU usage and the speed of the ball. Each loop a circle is drawn while the previous one is erased when the coordinates change. _DISPLAY only shows the new circle position once each loop. The '''_DISPLAY''' routine eliminates the need for setting [[SCREEN (statement)|SCREEN]] swap pages, [[CLS]] and [[PCOPY]]. _DISPLAY keeps the image off of the screen until the changes have all completed. Drawing 40 circles every loop helps slow down the ball.
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{{PageSeeAlso}}
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* [[_AUTODISPLAY]] {{text|(default mode)}}
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* [[PCOPY]]
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* [[_DISPLAY (function)]]
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{{PageNavigation}} |