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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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package org.lwjgl.examples.spaceinvaders;
/**
* An entity which represents one of our space invader aliens.
*
* @author Kevin Glass
* @author Brian Matzon
*/
public class AlienEntity extends Entity {
/** Movement made downwards when a border is hit */
private static final int DOWNWARD_MOVEMENT = 10;
/** Border at which player dies */
private static final int BOTTOM_BORDER = 570;
/** Right border at which to shift direction */
private static final int RIGHT_BORDER = 750;
/** Left border at which to shift direction */
private static final int LEFT_BORDER = 10;
/** The speed at which the alient moves horizontally */
private float moveSpeed = 75;
/** The game in which the entity exists */
private Game game;
/** The animation frames */
private Sprite[] frames = new Sprite[4];
/** The time since the last frame change took place */
private long lastFrameChange;
/** The frame duration in milliseconds, i.e. how long any given frame of animation lasts */
private long frameDuration = 250;
/** The current frame of animation being displayed */
private int frameNumber;
/**
* Create a new alien entity
*
* @param game The game in which this entity is being created
* @param x The intial x location of this alien
* @param y The intial y location of this alient
*/
public AlienEntity(Game game, int x, int y) {
super(game.getSprite("alien.gif"), x, y);
// setup the animatin frames
frames[0] = sprite;
frames[1] = game.getSprite("alien2.gif");
frames[2] = sprite;
frames[3] = game.getSprite("alien3.gif");
this.game = game;
dx = -moveSpeed;
}
/**
* Request that this alien moved based on time elapsed
*
* @param delta The time that has elapsed since last move
*/
public void move(long delta) {
// since the move tells us how much time has passed
// by we can use it to drive the animation, however
// its the not the prettiest solution
lastFrameChange += delta;
// if we need to change the frame, update the frame number
// and flip over the sprite in use
if (lastFrameChange > frameDuration) {
// reset our frame change time counter
lastFrameChange = 0;
// update the frame
frameNumber++;
if (frameNumber >= frames.length) {
frameNumber = 0;
}
sprite = frames[frameNumber];
}
// if we have reached the left hand side of the screen and
// are moving left then request a logic update
if ((dx < 0) && (x < LEFT_BORDER)) {
game.updateLogic();
}
// and vice vesa, if we have reached the right hand side of
// the screen and are moving right, request a logic update
if ((dx > 0) && (x > RIGHT_BORDER)) {
game.updateLogic();
}
// proceed with normal move
super.move(delta);
}
/**
* Update the game logic related to aliens
*/
public void doLogic() {
// swap over horizontal movement and move down the
// screen a bit
dx = -dx;
y += DOWNWARD_MOVEMENT;
// if we've reached the bottom of the screen then the player
// dies
if (y > BOTTOM_BORDER) {
game.notifyDeath();
}
}
/**
* Notification that this alien has collided with another entity
*
* @param other The other entity
*/
public void collidedWith(Entity other) {
// collisions with aliens are handled elsewhere
}
}