Question

I have a Sprite that contains opaque objects surrounded by transparent pixels. I also have a Rectangle that represents a part of the Sprite that I want to render using BitmapData.draw().

The problem is that the Rectangle that I obtained also contains transparent parts. How can I narrow the Rectangle to only include the opaque parts and ignore the transparent surroundings?

kapep’s answer is just what I want to do, but the problem is that the source is a Sprite, not a BitmapData object, and I don’t have getColorBoundsRect() on a Sprite.

Answer 1

You can use getColorBoundsRect for this.

var mask:uint = 0xFF000000; // ignore rgb, use alpha only
var transparent = 0x00000000; 
var rect:Rectangle = imageBitmapData.getColorBoundsRect(mask, transparent, false);

To operate with the pixels of the sprite, it needs to be drawn to a BitmapData first (use BitmapData.draw). Then after getting a smaller rectangle with getColorBoundsRect, create a new BitmapData with the dimensions of that rectangle. The last step is to use copyPixels, to copy the area of the rectangle from first image to the new one.

var imageBitmapData:BitmapData = new BitmapData(image.width, image.height, true, 0);
imageBitmapData.draw(image);
// var rect =  ... as above
var resultBitmapData:BitmapData = new BitmapData(rect.width, rect.height, true, 0);
resultBitmapData.copyPixels(imageBitmapData, rect, new Point(0,0));