The _DISPLAY statement turns off automatic display while only displaying the screen changes when called.
- _DISPLAY turns off the default _AUTODISPLAY when used. Prevents screen flickering.
- _DISPLAY tells QB64GL to render all of the hardware _PUTIMAGE commands loaded into the buffer previously.
- 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.