What you have learned
In the previous module, you learned how to use the following methods of the Input class to get user input:
- isKeyDown
- isMouseButtonDown
- getMouseX
- getMouseY
What you will learn
In this module, you will learn how to use objects of the SpriteSheet class and the Animation class to perform simple sprite sheet animation. In the next module, you will learn how to performmore complex animation.
General background information
The SpriteSheet class
Sprite sheets are individual sprites (or images) combined into a single image as shown in Figure 1 . Slick2D provides the SpriteSheet class that makes it relatively easy for you to access each of the sub-images of the sheet as separate imagesin your program.
The SpriteSheet class assumes that all the images are evenly spaced. It splits the source image into an even grid of cells and allows you to access the image in each cell as a separate image.
(Slick2D also provides the capability to work with packed sprite sheets with fewer restrictions on the organization of the sprite sheet.)
The Animation class
A series of images
Since well before the first Disney movies, animations have been created by displaying a series of images one after theother.
Each image (or frame) is typically displayed for the same amount of time, but that is not always the case, as will be demonstrated by the program in thenext module.
Slick2D provides a class named Animation that does most of the heavy lifting in the display of an animation.
Create, populate, and configure the object
There are several different ways to create, populate, and configure an Animation object containing a series of images, with the same or different display durations for the images.
Displaying the images
By default, calling one of several overloaded draw methods on the Animation object causes it to display the sequence of images and to start over when the last image has been displayed. However, that behaviorcan be overridden in order to provide more customized behavior.
(It is actually more complicated that that, as you will see later in the discussion of the render method.)
Animations can be stopped, started and restarted (returning to the first frame of the animation) . The capabilities of the Animation class go far beyond those illustrated in this module and the next.
Discussion and sample code
The class named Slick0180
Will discuss in fragments
A complete listing of the program named Slick0180 is provided in Listing 8 . I will break the program down and discuss it in fragments.
Listing 1 shows the beginning of the class named Slick0180 down through the main method.
| Listing 1 . Beginning of the class named Slick0180. |
|---|
public class Slick0180 extends BasicGame{
Image spriteSheetImage = null;float spriteSheetWidth;
float spriteSheetHeight;int spritesPerRow = 5;
int spritesPerColumn = 2;int targetDelta = 16;//msec
int duration = 200;//time to display each spritelong totalTime = 0;//accumulate total time for display
SpriteSheet spriteSheet;Animation animation;
int spriteWidth;int spriteHeight;
float spriteX = 0;//sprite drawing locationfloat spriteY = 0;
//----------------------------------------------------//public Slick0180(){
//Call to superclass constructor is required.super("Slick0180, Baldwin.");
}//end constructor//----------------------------------------------------//
public static void main(String[]args)
throws SlickException{AppGameContainer app = new AppGameContainer(
new Slick0180(),450,120,false);app.start();//this statement is required
}//end main |