Creating an Optimized Post-Retro Game - The Essential Guide to Flash Games - page 518

We very well could scroll the screen using the scrollRect property of the Sprite holder instance.
However, we would lose the reusability of the canvasBitmapData world BitmapData canvas. With
the scrollable Sprite canvas and individual Sprite objects attached to its display list we would
have had to draw the Sprite holder's contents into a radarBD BitmapData on every frame we
wanted to update the radar. Alternatively, we could have created a miniature version of the
Sprite holder with a second Sprite object to represent each Sprite canvas object. Both of these
ideas would be OK implementations, but they would be much slower than just reusing the
canvasBitmapData as the BitmapData reference for out radarBitmap .

Obviously, the method of using a second Bitmap object to display the entire game world as a
radar only works if you want the radar screen to be a miniature version of the actual game
screen. If you want the radar to be an abstract representation of the game screen, you will have
to employ a different method.

When we create our radarBitmap , we set the reference to the canvasBitmapData :
private var radarBitmap:Bitmap = new Bitmap(canvasBitmapData);
As long as the canvasBitmapData has already been created, this line of code will work fine.
In the init function, we simply resize and place the radarBitmap on the screen. We then never
have to worry about it again. It will always be updated when the canvasBitmapData is updated.
radarBitmap.x = 420;
radarBitmap.y = 230;
radarBitmap.scaleX = .2;
radarBitmap.scaleY = .2;
addChild(radarBitmap);

Creating the new game classes
The following classes, although created for this specific game's needs, are engineered to be
generic pieces that can be reused by any game that needs them. Some will be added to the
framework, and some will be in the Blaster Mines package.

Designing the BlitArrayAsset class
The BlitArrayAsset class is located in com.efg.famework and is the equivalent of a TileSheet for
assets created in code. This helper class is used only to create arrays of assets. Instances of this
class will always be temporary and only local to the functions that we create them in. The class
doesn't even need a constructor; it is used like a library. BlitArrayAsset will be added to the
framework package and will have two public functions. The first is
public function createRotationBlitArrayFromBD(sourceBitmapData:BitmapData, inc:int,

offset:int = 0):Array {
This function requires a BitmapData ( sourceBitmapData ) instance to be passed in along with an
increment value and an angle offset for creating the rotation. The BitmapData represents a static
graphic that will be turned into an array of rotated BitmapData values. The inc (or increment value)
represents the degrees to skip on each object rotation. For example, an inc value of 1 would create
an array of 360 rotations (offset by 1 degree each), while an inc value of 10 would only create an
array of 36 rotations (offset by 10 degrees each).