_DISPLAY - QB64 Wiki

_DISPLAY

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


Contents

Syntax

_DISPLAY


Description

  • _DISPLAY turns off the auto refresh screen default _AUTODISPLAY behavior. Prevents screen flickering.
  • Call _DISPLAY each time the screen graphics are to be displayed. Place call after the image has been changed.
  • Re-enable automatic display refreshing by calling _AUTODISPLAY. If it isn't re-enabled, things may not be displayed later.
  • _DISPLAY tells QB64 to render all of the hardware _PUTIMAGE commands loaded into the buffer previously.
  • The _AUTODISPLAY (function) can be used to detect the current display behavior.
  • QB64 can set the graphic rendering order of _SOFTWARE, _HARDWARE, and _GLRENDER with _DISPLAYORDER.


Examples

Example 1: 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.


Example 2: _DISPLAY must be used to render hardware images placed with _PUTIMAGE (version 1.000 and up).

CONST MenuHeight = 200 SCREEN _NEWIMAGE(640, 480, 32) 'SLEEP 1 LOCATE 20 DO _LIMIT 30 DisplayMenu k = _KEYHIT IF k <> 0 THEN PRINT k, LOOP UNTIL k = 32 OR k = 27 SUB DisplayMenu STATIC init, MS_HW AS LONG IF NOT init THEN init = -1 MS = _NEWIMAGE(640, MenuHeight, 32) 'MenuScreen image D = _DEST: _DEST MS CLS , &HFFAAAAAA 'background color gray _PRINTSTRING (20, 2), "Menu Test" 'image text MS_HW = _COPYIMAGE(MS, 33) 'create the MenuScreen_HardWare image _FREEIMAGE MS _DEST D END IF _PUTIMAGE (0, 0)-(640, MenuHeight), MS_HW _DISPLAY END SUB

Code adapted by Galleon
Notes: When _DISPLAY is commented out, the hardware Menu Test screen portion will blink and key codes may be seen underneath.


See also



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