positioning bitmapdata - actionscript-3

Question

I have the following code:
public function Application()
{
loader = new Loader();
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, completeHandler);
var urlRequest:URLRequest = new URLRequest("image/1.jpg");
loader.load(urlRequest);
addChild(loader);
}
private function completeHandler(e:Event):void{
loader.content.width = 800;
loader.content.scaleY = loader.content.scaleX;
piece = Math.round(loader.height/10);
drawBitmaps();
}
private function drawBitmaps():void{
var bmdata:BitmapData = new BitmapData(loader.width, piece, true, 0x000000);
bmdata.draw(loader);
var bitmap:Bitmap = new Bitmap(bmdata);
addChild(bitmap);
loader.visible = false;
}
the result is a bitmap wich contains a pice of the image. The height is 80. and it starts at the top of the image. But how can i tell the bitmapdata to start drawing the image from lets say 80pixels? so it draws a middle piece of the image? Because atm it allways draws from the top of the image.

Answer 1

You should use BitmapData::draw clipRect parameter.
Here is an example:
package {
import flash.geom.Rectangle;
import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.display.Graphics;
import flash.display.Sprite;
public class BitmapDataTest extends Sprite {
public function BitmapDataTest() {
var c:Sprite = new Sprite();
var g:Graphics;
g = c.graphics;
g.beginFill(0xFF0000);
g.drawCircle(30,30,30);
g.endFill();
addChild(c);
c.x = 10;
c.y = 10;
var bmdata:BitmapData = new BitmapData(60, 60, true, 0x000000);
bmdata.draw(c,null,null,null, new Rectangle(0,30,30,30));
var bitmap:Bitmap = new Bitmap(bmdata);
addChild(bitmap);
bitmap.x = 80;
bitmap.y = 10;
}
}
}
Please notice that the target bitmap data should have the same dimensions as source or this won't work. If you really have to cut it down you should use BitmapData::copyPixels method.

Answer 2

The easiest way would be to apply a mask, dynamically. Here is a good example: Actionscript 3 and dynamic masks
You can create a rectangle, the height you're looking for and position it appropriately.
Hope this helps.