Actionscript – How to load a bitmap file into a BitmapData object

To fix the OutOfMemory error, you should do something like this:

BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 8;
Bitmap preview_bitmap = BitmapFactory.decodeStream(is, null, options);

This inSampleSize option reduces memory consumption.

Here's a complete method. First it reads image size without decoding the content itself. Then it finds the best inSampleSize value, it should be a power of 2, and finally the image is decoded.

// Decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
    try {
        // Decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(f), null, o);

        // The new size we want to scale to
        final int REQUIRED_SIZE=70;

        // Find the correct scale value. It should be the power of 2.
        int scale = 1;
        while(o.outWidth / scale / 2 >= REQUIRED_SIZE && 
              o.outHeight / scale / 2 >= REQUIRED_SIZE) {
            scale *= 2;
        }

        // Decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
    } catch (FileNotFoundException e) {}
    return null;
}

First of all, BitmapData and Bitmap are not interchangeable. They are two very different things. The BitmapData class contains bitmap pixel data, and allows you to manipulate that pixel data, e.g. draw to it, change the color of particular pixels, et c. There is no way of displaying a BitmapData directly, i.e. by adding it to the display list.

The Bitmap class, on the other hand, is a DisplayObject, like MovieClips and Sprites, which you can add to the display list. It's single purpose is to render a BitmapData in the display list. In fact, it is not even interactive, so you cannot detect clicks directly on a Bitmap instance, for example.

On to your question: If you have a bitmap data that contains a tile sprite, and you want to draw that tile in another bitmapdata, you can use the BitmapData.draw() method, or the BitmapData.copyPixels() method. The latter is one of the fastest methods you can use on any BitmapData, so I would highly recommend it.

Depending on your particular application, it might not be beneficial to draw everything in a bitmap at all. It sounds as if you want to be able to detect click events on all the tiles, which makes me think that you would probably benefit from having them be separate DisplayObjects, e.g. Sprites.

If you want to, you can create a Tile class that extends Sprite, and draws a BitmapData using a bitmap fill. That way, you can have any properties you want, and also detect mouse events on the tile instances.

package
{
  /* ... imports ... */

  public class Tile extends Sprite 
  {
    private var _solid : Boolean;

    public function Tile(bmp : BitmapData, solid : Boolean)
    {
      this.graphics.beginBitmapFill(bmp, null, false, true);
      this.graphics.drawRect(0, 0, bmp.width, bmp.height);

      _solid = solid;
    }

    /**
     * Sample custom property. Could be used to define whether a tile
     * is solid, e.g. the player cannot pass it.
    */
    public function get isSolid() : Boolean
    {
      return _solid;
    }
  }
}

This class could simply be instantiated for every tile in your game, passing in the bitmap data that should be drawn in the tile. You could also listen for events on such a tile instance.

var tile : Tile;

tile = new Tile(myBitmapData, false);
tile.x = 200;
tile.y = 200;
tile.addEventListener(MouseEvent.CLICK, handleTileClick);

addChild(tile);

This way, you don't have to use the Bitmap class at all to render the tiles. They can be added directly to the display list.