Difference between revisions of "DISPLAY"

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     {{Cl|_LIMIT}} 100      ' set to 100 frames per second
     {{Cl|_LIMIT}} 100      ' set to 100 frames per second
     x = x + dx: y = y + dy
     x = x + dx: y = y + dy
     {{Cl|IF...THEN|IF}} x < 0 {{Cl|OR}} x > 640 {{Cl|THEN}} dx = -dx 'limit columns
     {{Cl|IF...THEN|IF}} x < 0 {{Cl|OR}} x > 640 {{Cl|THEN}} dx = -dx 'limit columns and reverse column direction each side
     {{Cl|IF...THEN|IF}} y < 0 {{Cl|OR}} y > 480 {{Cl|THEN}} dy = -dy 'limit rows
     {{Cl|IF...THEN|IF}} y < 0 {{Cl|OR}} y > 480 {{Cl|THEN}} dy = -dy 'limit rows and reverse row direction top or bottom
     IF px <> x OR py <> y THEN FOR d = 1 to 20: CIRCLE (px, py), d, 0: NEXT 'erase
     IF px <> x OR py <> y THEN FOR d = 1 to 20: CIRCLE (px, py), d, 0: NEXT 'erase
     FOR c = 1 TO 20: {{Cl|CIRCLE}} (x, y), c, 6: NEXT  'draw new circle at new position
     FOR c = 1 TO 20: {{Cl|CIRCLE}} (x, y), c, 6: NEXT  'draw new circle at new position

Revision as of 23:01, 12 July 2010

The _DISPLAY statement turns off automatic display while only displaying the screen graphics when called.


== Syntax == _DISPLAY


Description

  • _DISPLAY turns off the default _AUTODISPLAY when used. Prevents screen flickering.
  • Call _DISPLAY each time the screen graphics are to be displayed. Place call after the image has been changed.
  • Re-enable the automatic display by calling _AUTODISPLAY.


Examples: Displaying a circle bouncing around the screen.

SCREEN 12 x = 21: y =31 'start position dx = 3: dy = 3 'number of pixel moves per loop DO _LIMIT 100 ' set to 100 frames per second x = x + dx: y = y + dy IF x < 0 OR x > 640 THEN dx = -dx 'limit columns and reverse column direction each side IF y < 0 OR y > 480 THEN dy = -dy 'limit rows and reverse row direction top or bottom IF px <> x OR py <> y THEN FOR d = 1 to 20: CIRCLE (px, py), d, 0: NEXT 'erase FOR c = 1 TO 20: CIRCLE (x, y), c, 6: NEXT 'draw new circle at new position px = x: py = y 'save older coordinates to erase older circle next loop _DISPLAY 'after new circle is set, show it LOOP UNTIL INKEY$ = CHR$(27)

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 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.


See also



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