Difference between revisions of "DISPLAY"

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''Examples:'' Displaying a circle bouncing around the screen.
''Examples:'' Displaying a circle bouncing around the screen.
{{CodeStart}}
{{CodeStart}} '' ''
 
{{Cl|SCREEN (statement)|SCREEN}} 12
{{Cl|SCREEN (statement)|SCREEN}} 12
x = 21: y =31              'start position
x = 21: y =31              'start position
dx = 3: dy = 3            'number of pixel moves per loop       
dx = 3: dy = 3            'number of pixel moves per loop       
{{Cl|DO}}
{{Cl|DO}}
     {{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
Line 27: Line 26:
     px = x: py = y        'save older coordinates to erase older circle next loop
     px = x: py = y        'save older coordinates to erase older circle next loop
     {{Cl|_DISPLAY}}                'after new circle is set, show it
     {{Cl|_DISPLAY}}                'after new circle is set, show it
{{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|INKEY$}} = CHR$(27)
{{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|INKEY$}} = CHR$(27) '' ''
 
{{CodeEnd}}
{{CodeEnd}}



Revision as of 01:12, 4 October 2012

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


Syntax

'_DISPLAY


Usage:

  • _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. If it isn't re-enabled, things may not be displayed later!


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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