Laying the Groundwork for No Tanks! - The Essential Guide to Flash Games - page 246

The blitPoint is used in copyPixels blitting operations to specify the top-left (x,y) position to start
the painting of a tile sheet tile onto the canvasBitmap . The tileBlitRectangle will be used to
specify the top-left (x,y) position on the tile sheet to start copying the 32 32-pixel Rectangle .

This Rectangle will be placed on the canvasBitmap at the blitPoint . You have seen the
tileSheet variable before; we instantiate the tileSheet by passing it an instance of the library
item TankSheetPng along with width and height for our tile.

The constructor
The new constructor adds in code to call some new functions.
public function GameDemo() {
initTileSheetData();
readBackGroundData();
readSpriteData();
drawLevelBackGround();
addChild(canvasBitmap);
}
First, we will read the background data in from the Level instance. Next, we will call a stub
version of the readSpriteData function. We will not be implementing this function in this chapter,
but we want to make sure we point out that the sprite data is not read in when we read in the
background data. We will next draw our background to the canvasBitmapData with the
drawLevelBackGround function and finally add the canvasBitmap to the stage.

The readBackGroundData function
The readBackGroundData function is completely new. We will use it to read through our level data
and create the 2D levelTileMap array.
private function readBackGroundData():void {
levelTileMap = [];
levelData = levels[level];
levelTileMap = levelData.backGroundMap;
}
The readBackGroundData function is very simple. In Chapter 7, we will add code to read more of
the level-specific variables from the Level class instance, but for now, we will keep it very simple.
We first initialize the levelTileMap array by assigning it the shortcut [] value. Next, we place a
reference to the current Level object into the levelData Level class instance. Finally, we simply
assign the levelTileMap array to reference the levelData.backGroundMap array. That is all we
need to do to start using the level data.

The readSpriteData function
The readSpriteData function is only a stub placeholder that we will fill in when we get to Chapter 7.
private function readSpriteData():void {
//place holder for reading sprite data and placing sprites on the screen
}