AS3 BitmapData Copy Pixels Half Pixel?

Question

Having trouble trying to scroll BitmapData on a half pixel here is my original code

var speed:Number = 1;
_bitmapData.copyPixels(_backgroundParallax, _screenRect, _zeroPoint, null, null, true);
_backgroundParallax.copyPixels(_backgroundParallax, new Rectangle(0, 0, speed,    _backgroundParallax.height), new Point(_backgroundParallax.width-speed,0), null, null, false);
_backgroundParallax.scroll( (speed*-1) , 0);

which works until i change the var speed to .5, which is because .scroll method is expecting int's so i replicated what scroll is doing to try and allow .5 pixels

var speed:Number = 1;
_bitmapData.copyPixels(_backgroundParallax, _screenRect, _zeroPoint, null, null, true);
_backgroundParallax.copyPixels(_backgroundParallax, new Rectangle(0, 0, speed,    _backgroundParallax.height), new Point(_backgroundParallax.width-speed,0), null, null, false);
_backgroundParallax.copyPixels(_backgroundParallax, new Rectangle(0, 0, _backgroundParallax.width, _backgroundParallax.height), new Point((speed*-1),0), null, null, false);

which again works great when the speed is 1, but again doesn't move at all when it is set to .5

Any ideas?

unfortunately for pixels there is no half size. maybe you can use some math to slow down things. — Adrian Pirvulescu
Are you trying to call this code multiple times to scroll the bitmap, but want to slow the execution speed? — sch
@AdrianPirvulescu Thought so! I'll slow it down by other means. Cheers — rorypicko

Plastic Sturgeon Plastic Sturgeon · Accepted Answer · 2012-02-17T20:08:56

You won't be able to get smooth half-pixel scrolling with the approach you are using. But I have developed two alternatives using transform matrix that work really really well.

Here are two different approaches to scrolling:

This approach scrolls a single image to its limits. http://plasticsturgeon.com/2010/11/super-fast-scrolling-of-huge-bitmaps/

This approach scrolls a tiled image infinitely. http://plasticsturgeon.com/2010/06/infinite-scrolling-bitmap-backgrounds-in-as3/

Working demos, explanation and complete downloadable source code provided on the links

AS3 BitmapData Copy Pixels Half Pixel?

1 Answers