actor.java

《J2ME Game Programming》随书光盘源代码

import net.jscience.math.kvm.MathFP;
import javax.microedition.lcdui.*;

/**
 * An abstract base class for higher level Actors. This class handles basic
 * position as well as maintaining a link to the GameScreen. A class extending
 * this needs to implement the render, getHeight and getWidth methods as well
 * as optionally overriding other methods like cycle to implement custom logic.
 * @author Martin J. Wells.
 */
abstract public class Actor
{
   public static final int FP_PI2 = MathFP.mul(MathFP.PI, MathFP.toFP(2));
   public static final int FP_DEGREES_PER_RAD = MathFP.div(MathFP.toFP(360), FP_PI2);
   public static final int FP_ONE = MathFP.toFP(1);

   private int xFP, yFP;               // current position (as a MathFP)
   private int lastXFP, lastYFP;       // last position (used by cycle code)
   private int realDir;                // actual direction in degrees
   private int alignedDir;             // aligned direction
   private int alignedDivDegreesFP;   	// degrees per facing division
   private boolean wantAlignment;		// turn auto alignment on
   private int spinFP;                 // current spin rate (can be negative)
   private int maxSpinRate;           	// maximum spin rate (in degrees per second)
   private int xVelFP, yVelFP;         // current velocity
   private int xAccFP, yAccFP;        	// current acceleration
   private int maxVelFP;
   private int thrustFP;
   private int bounceVelFP;              // The amount of bounce when we hit
                                       // something.

   private boolean autoSpinning;			// we set a flag to avoid over calling
                                       // setSpin()
   private int targetAngle;

   private long fluff = 0;

   /**
    * Constructs an Actor at position x, y facing direction d and setting
    * a maximum velocity and starting thrust. (Note the maxVelFPArg and
    * thrustFPArg both must be MathFP values.) The alignedDivArg sets the
    * number of distinct angles this Actor can face. A Ship with 16 facing
    * images has 16 aligned divisions, which translates to an aligned division
    * of 22.5 degrees (360 divided by 16). The aligned direction is used by the
    * Actor class to make sure it can only face an angle that can be drawn.
    * @param startX The starting x position of the new Actor.
    * @param startY The starting y position of the new Actor.
    * @param startDirection The starting direction
    * @param alignedDivArg The number of aligned angle divisions.
    * @param maxVelFPArg The maximum velocity.
    * @param thrustFPArg The starting thrust.
    * @param bounceVelFPArg The level of bounce when colliding with something.
    * @param maxSpinRateArg The maximum turn rate in degrees per second.
    */
   public Actor(int startX, int startY, int startDirection, int alignedDivArg,
                int thrustFPArg, int speedFPArg, int maxVelFPArg,
                int bounceVelFPArg, int maxSpinRateArg)
   {
      xFP = MathFP.toFP(startX);
      yFP = MathFP.toFP(startY);

      maxVelFP = maxVelFPArg;
      thrustFP = thrustFPArg;

      wantAlignment = false;
      if (alignedDivArg > 0)
      {
         alignedDivDegreesFP = MathFP.div(360, alignedDivArg);
         wantAlignment = true;
      }
      setDirection(startDirection);
      maxSpinRate = maxSpinRateArg;
      bounceVelFP = bounceVelFPArg;

      setVel(speedFPArg);
   }

   /**
    * Changes the current speed of the actor by setting the velocity based on
    * the current (aligned) direction.
    * @param speedFPArg The speed to travel at (as a MathFP value).
    */
   public final void setVel(int speedFPArg)
   {
      xVelFP = MathFP.mul(speedFPArg,
                          MathFP.cos(getRadiansFromAngle(alignedDir)));
      yVelFP = MathFP.mul(speedFPArg,
                          -MathFP.sin(getRadiansFromAngle(alignedDir)));

      // If you change this remember to change the cycle code
      if (xVelFP > maxVelFP)
         xVelFP = maxVelFP;
      else if (xVelFP < -maxVelFP) xVelFP = -maxVelFP;
      if (yVelFP > maxVelFP)
         yVelFP = maxVelFP;
      else if (yVelFP < -maxVelFP) yVelFP = -maxVelFP;
   }

   /**
    * Abstract render method that must be implemented by derived classes.
    * This method is intended to be called by a Actor manager (such as a
    * World class) to draw Actors on the screen.
    * @param graphics The graphics context upon which to draw.
    */
   abstract public void render(Graphics graphics);

   /**
    * Gets the spin rate for this Actor in degrees per second.
    * @return The current spin (turning) rate.
    */
   public int getSpin()
   {
      return MathFP.toInt(spinFP);
   }

   /**
    * Set the spin rate for this Actor in degrees per second.
    * @param newSpin The spin rate.
    */
   public void setSpin(int newSpin)
   {
      spinFP = MathFP.toFP(newSpin);
   }

   /**
    * Sets this Actors spin rate to be the maximum (set in the constructor).
    */
   public final void setPeakSpin()
	{
		spinFP = MathFP.toFP(maxSpinRate);
	}

   /**
    * Sets this Actors spin rate to be the negative maximum (set in the
    * constructor). Use this to spin the Actor backwards (counter clockwise).
    */
	public final void setNegPeakSpin()
	{
		spinFP = MathFP.toFP(-maxSpinRate);
	}

   /**
    * Set an angle this actors wants to face; the actor will start spinning
    * at its default spin rate towards the target angle - see cycle for
    * the actual spin code.
    */
   public final void setTargetDirection(int angle)
   {
      targetAngle = angle;
      autoSpinning = false;
   }

   /**
    * A cycle method that moves the Actor a distance relative to it's current
    * speed (the value of the speed int) and the amount of time that has passed
    * since the last call to cycle (deltaMS). This code uses a fluff value in
    * order to remember values too small to handle (below the tick level).
    * @param deltaMS The number of milliseconds that have passed since the last
    * call to cycle.
    */
   public void cycle(long deltaMS)
   {
      int ticks = (int) (deltaMS + fluff) / 100;

      // remember the bit we missed
      fluff += (deltaMS - (ticks * 100));

      if (ticks > 0)
      {
         int ticksFP = MathFP.toFP(ticks);

         // move towards our target direction, if we have one
         if (targetAngle != 0)
         {
            if (!autoSpinning)
            {
               // start spin in the dir of the target angle
               setSpin(isClockwise(getDirection(),
                                   targetAngle) ? -maxSpinRate : maxSpinRate);
            }

            // and check if we've made it to the target direction
            if (getAlignedDirection(targetAngle) == getDirection())
            {
               setSpin(0);
               setTargetDirection(0);
               autoSpinning = false;
            }
         }

         // spin based on degrees per tick
         if (spinFP != 0)
            setDirection(getRealDirection() +
                         MathFP.toInt(MathFP.mul(ticksFP, spinFP)));

         // move based on our speed in pixels per ticks
         if (thrustFP != 0)
         {
            // Calculate the acceleration for this cycle by multiplying the direction
            // by the thrust on both x and y.
            xAccFP = MathFP.mul(thrustFP, MathFP.cos(getRadiansFromAngle(alignedDir)));
            yAccFP = MathFP.mul(thrustFP, -MathFP.sin(getRadiansFromAngle(alignedDir)));

            // Increase the velocity by the amount of acceleration in this cycle.
            xVelFP = MathFP.add(xVelFP, xAccFP);
            yVelFP = MathFP.add(yVelFP, yAccFP);
         }

         // Fix the velocity to the maximum if it currently exceeds it.
         if (xVelFP > maxVelFP)
            xVelFP = maxVelFP;
         else if (xVelFP < -maxVelFP) xVelFP = -maxVelFP;
         if (yVelFP > maxVelFP)
            yVelFP = maxVelFP;
         else if (yVelFP < -maxVelFP) yVelFP = -maxVelFP;

         lastXFP = xFP;
         lastYFP = yFP;

         // adjust X
         xFP = MathFP.add(xFP, MathFP.mul(xVelFP, ticksFP));

         // Wrap around the world.
         if (MathFP.toInt(xFP) > GameScreen.getGameScreen().getWidth())
            xFP = MathFP.toFP(0);
         else if (MathFP.toInt(xFP) < 0)
            xFP = MathFP.toFP(GameScreen.getGameScreen().getWidth());
         // now check if we collided with anything (we test X first)
         else if (GameScreen.getGameScreen().checkCollision(this))
         {
            xVelFP = MathFP.mul(xVelFP, bounceVelFP);
            xFP = MathFP.add(lastXFP, xVelFP);
         }

         // adjust Y
         // we also handle a special case where the x collision may have
         // caused the ship to move (teleport, gateway). In this case our