2D Game Programming Tricks - Beginning Android Games - page 422

We can easily do this with our TextureRegion and SpriteBatcher classes. Usually, we'd not only
have a single animation, like the one in Figure 8-25 , but many more in a single atlas. Besides
the walk animation, we could have a jump animation, an attack animation, and so on. For each
animation, we need to know the frame duration, which tells us how long to keep using a single
keyframe of the animation before switching to the next frame.

The Animation Class
Let us define the requirements for an Animation class, which stores the data for a single
animation, such as the walk animation in Figure 8-25 :

ï?® Animation holds a number of TextureRegion s, which store where each
keyframe is located in the texture atlas. The order of the TextureRegion s is
the same as that used for playing back the animation.

An

ï?® Animation also stores the frame duration, which has to pass before we
switch to the next frame.

The

ï?® Animation should provide us with a method to which we pass the time
we've been in the state that the Animation represents (for example, walking
left), and that will return the appropriate TextureRegion . The method should
take into consideration whether we want the Animation to loop or to stay at
the last frame when the end is reached.
This last bullet point is important because it allows us to store a single Animation instance to
be used by multiple objects in our world. An object just keeps track of its current state, that is,
whether it is walking, shooting, or jumping, and how long it has been in that state. When we
render this object, we use the state to select the animation we want to play back and the state
time to get the correct TextureRegion from the Animation . Listing 8-19 shows the code of our
new Animation class.

The

Listing 8-19. Animation.java, a Simple Animation Class

package com.badlogic.androidgames.framework.gl;

public class Animation {
public static final int ANIMATION_LOOPING = 0;
public static final int ANIMATION_NONLOOPING = 1;

final TextureRegion[] keyFrames;
final float frameDuration;

public Animation( float frameDuration, TextureRegion ... keyFrames) {
this .frameDuration = frameDuration;
this .keyFrames = keyFrames;
}

public TextureRegion getKeyFrame( float stateTime, int mode) {
int frameNumber = ( int )(stateTime / frameDuration);