darron schall :: application developer specializing in the flash platform

Flash 8's ability to use bitmap / pixel data in the player is an awesome new feature addition. When you're doing a lot of pixel manipulation, here's a little trick to improve performance: Use an off-screen bitmap for setPixel and then copy the pixels into an on-screen bitmap.

Consider the following code snippet:

import flash.geom.Point;
import flash.display.BitmapData;
import flash.display.Bitmap;

var width:Number = 100;
var height:Number = 100;

var offScreen:BitmapData = new BitmapData(width, height);
var onScreen:BitmapData = new BitmapData(width, height);

var zeroPoint:Point = new Point(0, 0);

var clip:MovieClip = createEmptyMovieClip("clip", 1);
clip._x = 10;
clip._y = 10;
clip.attachBitmap(onScreen, 1); // wire the bitmap to the screen

onEnterFrame = function() {
 	// do all of the pixel manipulation in the offScreen BitmapData
 	for (var y:Number = 0; y < height; y++) {
  		for (var x:Number = 0; x < width; x++) {
   			offScreen.setPixel(x, y, x*y+getTimer());
   		}
  	}
 	
 	// as a final step, copy all of the offScreen pixels to the onScreen BitmapData
 	onScreen.copyPixels(offScreen, offScreen.rectangle, zeroPoint);
}

The difference may not be huge, but it does make a difference. This technique, drawing off screen and then copying on screen, is called Double Buffering.

Already making great use of BitmapData, have you see Andre's 8ball lab yet?