animation.java

J2ME MIDP_Example_Applications

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package example.postcard;

import java.lang.IllegalArgumentException;
import java.util.Random;
import javax.microedition.lcdui.*;


// A class representing the animated image that floats in the Postcard

class Animation
{
    private static final Random RANDOM = new Random();

    private final AnimationSequence animationSequence;
    private final int w;
    private final int h;
    private final int xBoundary;
    private final int yBoundary;
    private final int wBoundary;
    private final int hBoundary;

    private int currentIndex = 0;
    private int ticks = 0;
    private int ticksSinceLastChangeX = 0;
    private int ticksSinceLastChangeY = 0;
    private int x = 0;
    private int y = 0;
    private int dx = 1;
    private int dy = 1;


    // An Animation is constructed from a sequence of animation images.
    // The Animation can move with a box bounded by {xBoundary, yBoundary}
    // and {xBoundary+wBoundary, yBoundary+hBoundary}.
    //
    // The parameter animationSequence is the sequence of animation
    // images used to create the animation. The bounding box where the
    // animation is allowed to move is bounded by: xBoundary, yBoundary,
    // wBoundary and hBoundary.

    Animation(AnimationSequence animationSequence,
                    int xBoundary, int yBoundary, int wBoundary, int hBoundary)
        throws IllegalArgumentException
    {
        if (animationSequence == null)
        {
            throw new IllegalArgumentException("null AnimationSequence");
        }

        this.animationSequence = animationSequence;
        this.w = animationSequence.getMaxImageWidth();
        this.h = animationSequence.getMaxImageHeight();
        if (w < wBoundary)
        {
            x = (xBoundary + wBoundary - w)/2;
        }
        if (h < hBoundary)
        {
            y = (yBoundary + hBoundary - h)/2;
        }
        this.xBoundary = xBoundary;
        this.yBoundary = yBoundary;
        this.wBoundary = wBoundary;
        this.hBoundary = hBoundary;
        dx = rand(3) - 1; // 0, -1 or 1
        dy = rand(3) - 1; // 0, -1 or 1
    }


    void tick()
    {
        ticks++;
        ticksSinceLastChangeX++;
        ticksSinceLastChangeY++;

        if ((ticks % 5) == 0)
        {
            if ((++currentIndex) >= animationSequence.size())
            {
                currentIndex = 0;
            }
        }

        move();
    }


    private void move()
    {
        // mostly continue as we are, but sometimes randomly change
        if ((ticksSinceLastChangeX > 20) && (rand(20) == 0))
        {
            dx = rand(3) - 1; // 0, -1 or 1
            ticksSinceLastChangeX = 0;
        }

        // if moving would take us off-canvas left or right, reverse
        if (((x + dx) < xBoundary) || ((x + dx + w) > (xBoundary + wBoundary)))
        {
            dx = -dx;
            ticksSinceLastChangeX = 0;
        }


        // mostly continue as we are, but sometimes randomly change
        if ((ticksSinceLastChangeY > 20) && (rand(20) == 0))
        {
            dy = rand(2) * 2 - 1; // -1 or 1
            ticksSinceLastChangeY = 0;
        }

        // if moving would take us off-canvas top or bottom, reverse
        if (((y + dy) < yBoundary) || ((y + dy + h) > (yBoundary + hBoundary)))
        {
            dy = -dy;
            ticksSinceLastChangeY = 0;
        }

        x += dx;
        y += dy;
    }


    void draw(Graphics g)
    {
        Image image = animationSequence.elementAt(currentIndex);
        g.drawImage(image, x, y, (Graphics.LEFT | Graphics.TOP));
    }


    // This method does not generate true random numbers.

    static int rand(int scale)
    {
        return (RANDOM.nextInt() << 1 >>> 1) % scale;
    }
}