Instance variables
Listing 1 declares a number of instance variables. The purpose of these variables should become clear based on their names andtheir usage that I will discuss later.
The constructor and the main method
There is nothing new in the constructor and the main method in Listing 1 .
The init method
The init method begins in Listing 2 . The embedded comments should provide a sufficient explanation of the code in Listing 2 .
| Listing 2 . Beginning of the init method. |
|---|
public void init(GameContainer gc)
throws SlickException {spriteSheetImage = new Image("Slick0180a1.png");
//Enlarge the sprite sheet.Image temp = spriteSheetImage.getScaledCopy(580,224);
spriteSheetImage = temp;//Get, save, and display the width and the height
// of the sprite sheet.spriteSheetWidth = spriteSheetImage.getWidth();
spriteSheetHeight = spriteSheetImage.getHeight();System.out.println(
"spriteSheetWidth: " + spriteSheetWidth);System.out.println(
"spriteSheetHeight: " + spriteSheetHeight);//Compute the width and height of the individual// sprite images.
spriteWidth = (int)(spriteSheetWidth/spritesPerRow);spriteHeight =
(int)(spriteSheetHeight/spritesPerColumn); |
Create a SpriteSheet object
Listing 3 creates a new SpriteSheet object based on the sprite sheet image along with the width and height of the individual sprites.
| Listing 3 . Create a SpriteSheet object. |
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//Instantiate a new Spritesheet object based on the
// width and height of the tiles.spriteSheet = new SpriteSheet(spriteSheetImage,
spriteWidth,spriteHeight); |
Create a new Animation object
Listing 4 creates a new Animation object that will process the SpriteSheet object instantiated in Listing 3 .
| Listing 4 . Create a new Animation object. |
|---|
//Create a new animation based on a selection of
// sprites from the sprite sheet.animation = new Animation(spriteSheet,
0,//first column0,//first row
4,//last column0,//last row
true,//horizontalduration,//display time
true//autoupdate); |
Constructor parameters
Obviously, the first parameter to the constructor for the Animation class specifies the SpriteSheet object.
The second and third parameters specify that the first image in the sequence should be the top-left image in Figure 1 .
The fourth and fifth parameters specify that the last image in the sequence should be the top-right image in Figure 1 .
The true value for the sixth parameter specifies that the images should be scanned horizontally.
The duration value in the seventh parameter specifies that each image should be displayed for 200 milliseconds.
The true value for the last parameter specifies that the display should continue cycling through the images until the animation is stopped.
Set frame rate and display location
The code is Listing 5 sets the frame rate and specifies the drawing location. The drawing location is the locationwithin the game window where the sprite will be displayed.