Wired Movies and Sprites

Creating and Initializing a Sprite World

To create a sprite animation in an application, you first create a sprite world to contain your sprites. To do this, you perform the following steps:

Allocate a sprite layer graphics world that corresponds to the size and bit depth of your destination graphics world.
If you plan to have a background image behind your sprites that is static or that changes infrequently, create a background graphics world that is the same size and depth as the sprite layer graphics world. You do not need to do this if you plan to have a solid background color behind your sprites. Animations that use a solid background color require less memory and perform slightly better than animations that use a background image.
Call LockPixels on the pixel maps of the sprite layer and background graphics worlds. These graphics worlds must remain valid for the lifetime of the sprite world.
Call the NewSpriteWorld function to create the new sprite world.

The sample code function CreateSpriteStuff , shown in Listing 4-1 , calculates the bounds of the destination window and calls NewGWorld to create a new sprite layer graphics world. It then calls LockPixels to lock the pixel map of the sprite layer graphics world.

Next, CreateSpriteStuff calls NewSpriteWorld to create a new sprite world, passing the destination graphics world (WindowPtr ) and the sprite layer graphics world. CreateSpriteStuff passes a background color to NewSpriteWorld instead of specifying a background graphics world. The newly created sprite world is returned in the global variable gSpriteWorld.

Finally, CreateSpriteStuff calls the sample code function CreateSprites to populate the sprite world with sprites.

Listing 1 Creating a sprite world



 
// global variables

GWorldPtr spritePlane = nil;

SpriteWorld gSpriteWorld = nil;

Rect gBounceBox;

RGBColor gBackgroundColor;



void CreateSpriteStuff (Rect *windowBounds, CGrafPtr windowPtr)

{

    OSErr err;

    Rect bounds;

    

    // calculate the size of the destination

    bounds = *windowBounds;

    OffsetRect (&bounds, -bounds.left, -bounds.top);

    gBounceBox = bounds;

    InsetRect (&gBounceBox, 16, 16);



    // create a sprite layer graphics world with a bit depth of 16

    NewGWorld (&spritePlane, 16, &bounds, nil, nil, useTempMem);

    if (spritePlane == nil)

        NewGWorld (&spritePlane, 16, &bounds, nil, nil, 0);



    if (spritePlane) 

    {

        LockPixels (spritePlane->portPixMap);

        gBackgroundColor.red = gBackgroundColor.green =

            gBackgroundColor.blue = 0;



        // create a sprite world

        err = NewSpriteWorld (&gSpriteWorld, (CGrafPtr)windowPtr,

            spritePlane, &gBackgroundColor, nil);



        // create sprites

        CreateSprites ();

    }

}