The Game API - Beginning J2ME: From Novice to Professional - page 257

For example, you could add a layer to the top of the list by inserting a layer at index 0.
You can find the number of layers in the LayerManager by calling getSize() . If you'd like to
retrieve the layer at a certain position, pass the index to the getLayerAt() method.
Finally, you can remove a layer by passing the Layer object to the remove() method.
LayerManager includes the concept of a view window , which is the rectangular portion of
the scene that will be drawn. The assumption is that the overall scene is larger than the screen
of the device, so only a portion will be drawn at any time. By default, the view window has its
origin at 0, 0 and is as large as it can be ( Integer.MAX_VALUE for both width and height). You can
set the view window using the following method, where the x and y coordinates are relative to
the origin of the LayerManager .
public void setViewWindow(int x, int y, int width, int height)
To actually draw the scene represented by the LayerManager 's layers, call the paint() method:
public void paint(Graphics g, int x, int y)
The view window of the scene will be drawn using the given Graphics at the specified location,
which is specified in the coordinate system of the Graphics .
If you're still fuzzy on the relationship between a layer manager, its layers, and its view
window, see the API documentation for LayerManager , which contains two very helpful figures.
Using Tiled Layers
A tiled layer is made from a palette of tiles, just as you might assemble decorative tiles to create
a pretty design next to your bathtub. The tiles come from a single image that is divided into
equal-sized pieces.
A TiledLayer is drawn on a Graphics object using the paint() method inherited from Layer .
Like any other Layer , a tiled layer renders itself at its current location in the coordinate system
of the Graphics . Furthermore, like any other Layer , a tiled layer can be part of a LayerManager
and can be rendered automatically when the LayerManager is rendered using its paint() method.
For example, Figure 14-1 is 240 pixels wide and 96 pixels high.
Figure 14-1. A source image for a tiled layer
The image can be divided into 10 square tiles, each with a width and height of 48 pixels.
Tiles are numbered as shown in Figure 14-2.
Figure 14-2. Tile numbering