sprite.java

此文件是关于手机游戏开发的理论

import javax.microedition.lcdui.Graphics;

/**
 * A state manager for a game sprite. Use in conjunction with an ImageSet in
 * order to draw animated, multi-state sprites. For each instance of an animated
 * graphic you should create one corresponding Sprite object. Graphics are
 * shared using a common ImageSet. To animate you must call this class's cycle
 * method.
 * @author Martin J. Wells
 */
public class Sprite
{
   private int currentFrame;
   private int currentState;
   private long currentStateBegan;		// time this currentState started
   private ImageSet imageSet;
   private long lastFrameChange;
   private int totalCycles;

   /**
    * Constructor for a Sprite object requiring the source image set and the
    * starting state and frame.
    * @param is The imageSet which is the source of graphics for this Sprite.
    * @param startingState The starting state (normally 0).
    * @param startingFrame The starting frame (normally 0).
    */
   public Sprite(ImageSet is, int startingState, int startingFrame)
   {
      imageSet = is;
      setState(startingState, true);
      currentFrame = startingFrame;
   }

   /**
    * Change to a specific frame.
    * @param f The frame to change to.
    */
   public final void setFrame(int f)
   {
      currentFrame = f;
   }

   /**
    * Change to a different state.
    * @param s The state to change to.
    * @param force Normally we wont change change if that is already the current
    * state. However this has the effect of not reseting the state began time
    * and totalCycles counter. Set this to true to force those to be reset.
    */
   public final void setState(int s, boolean force)
   {
      if (currentState != s || force)
      {
         currentState = s;
         currentFrame = 0;
         totalCycles = 0;
         currentStateBegan = System.currentTimeMillis();
      }
   }

   /**
    * Resets all state information such as the current animation frame, total
    * number of completed cycles and the time the state began.
    */
   public final void reset()
   {
      currentFrame = 0;
      totalCycles = 0;
      currentStateBegan = 0;
      lastFrameChange = 0;
   }

   /**
    * Get the time the last state change occurred.
    * @return Time last state was changed in milliseconds since epoch.
    */
   public final long getWhenStateBegan()
   {
      return currentStateBegan;
   }

   /**
    * @return The total time spent in the current state.
    */
   public final long getTimeInCurrentState()
   {
      return (System.currentTimeMillis() - currentStateBegan);
   }

   /**
    * @return The current state.
    */
   public final int getCurrentState()
   {
      return currentState;
   }

   /**
    * @return The current frame number.
    */
   public final int getCurrentFrame()
   {
      return currentFrame;
   }

   /**
    * Draws the current sprite frame onto a specified graphics context.
    * @param target The target to draw the image frame onto.
    * @param targetX The target x position.
    * @param targetY The target y position.
    */
   public final void draw(Graphics target, int targetX, int targetY)
   {
      imageSet.draw(target, currentState, currentFrame, targetX, targetY);
   }

   /**
    * Cycles the current sprites animation and goes forward by the number of
    * frames corresponding to the amount of time that has elapsed.
    * @param deltaMS The amount of time that has passed in milliseconds.
    */
   public final void cycle(long deltaMS)
   {
      // change frame if we are animating (and enough time has passed)
      if (imageSet.getTotalFrames(currentState) > 1 &&
              imageSet.getAnimTime(currentState) > 0)
      {
         long deltaTime = System.currentTimeMillis() - lastFrameChange;
         if (deltaTime > imageSet.getAnimTimePerFrame(currentState))
         {
            currentFrame++;
            lastFrameChange = System.currentTimeMillis();
            if (currentFrame >= imageSet.getTotalFrames(currentState))
            {
               currentFrame = 0;
               totalCycles++;
            }
         }
      }
   }

   /**
    * @return The total number of cycles this sprite has animated through.
    * Very useful for determining if a sprite has finished it's animation.
    */
   public final int getTotalCycles()
   {
      return totalCycles;
   }
}