layer.java

J2ME 的Game包官方源代码。对改写Game包的会有一定价值[Game包不能用于MIDP1。0]

/*
 * @(#)Layer.java	1.27 02/08/30 @(#)
 *
 * Copyright (c) 2002 Sun Microsystems, Inc.  All rights reserved.
 * PROPRIETARY/CONFIDENTIAL
 * Use is subject to license terms.
 */

package javax.microedition.lcdui.game;

import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.Graphics;

/**
 * A Layer is an abstract class representing a visual element of a game. 
 * Each Layer has position (in terms of the upper-left corner of its visual 
 * bounds), width, height, and can be made visible or invisible.  
 * Layer subclasses must implement a {@link #paint(Graphics)} method so that 
 * they can be rendered.
 * <p>
 * The Layer's (x,y) position is always interpreted relative to the coordinate
 * system of the Graphics object that is passed to the Layer's paint() method. 
 * This coordinate system is referred to as the <em>painter's</em> coordinate 
 * system.  The initial location of a Layer is (0,0).
 *
 * <p>
 * @since MIDP 2.0
 **/
 
public abstract class Layer {

    /**
     * Creates a new Layer with the specified dimensions. 
     *
     * This constructor is declared package scope to
     * prevent developers from creating Layer subclasses
     *
     * By default, a Layer is visible and its upper-left  
     * corner is positioned at (0,0).
     * @param width The width of the layer, in pixels 
     * @param height The height of the layer, in pixels 
     *
     */
    Layer(int width, int height) {
        setWidthImpl(width);
        setHeightImpl(height);
    }	

    /**
     * Sets this Layer's position such that its upper-left corner
     * is located at (x,y) in the painter's coordinate system. 
     * A Layer is located at (0,0) by default.
     * <br>
     * @param x the horizontal position
     * @param y the vertical position
     * @see #move
     * @see #getX
     * @see #getY
     *
     */
    public void setPosition(int x, int y) {
        this.x = x;
        this.y = y;
    }

    /**
     * Moves this Layer by the specified horizontal and vertical distances.  
     * <br>
     * The Layer's coordinates are subject to wrapping if the passed 
     * parameters will cause them to exceed beyond Integer.MAX_VALUE 
     * or Integer.MIN_VALUE.
     * @param dx the distance to move along horizontal axis (positive
     * to the right, negative to the left)
     * @param dy the distance to move along vertical axis (positive
     * down, negative up)
     * @see #setPosition
     * @see #getX
     * @see #getY
     *
     */
    public void move(int dx, int dy) {	
        x += dx;
        y += dy;
    }

    /**
     * Gets the horizontal position of this Layer's upper-left corner
     * in the painter's coordinate system.
     * <p>
     * @return the Layer's horizontal position.
     * @see #getY
     * @see #setPosition
     * @see #move
     *
     */
    public final int getX() {
        return x;
    }

    /**
     * Gets the vertical position of this Layer's upper-left corner
     * in the painter's coordinate system.
     * <p>
     * @return the Layer's vertical position.
     * @see #getX
     * @see #setPosition
     * @see #move
     *
     */
    public final int getY() {
        return y;
    }

    /**
     * Gets the current width of this layer, in pixels.
     * @return the width in pixels
     * @see #getHeight
     *
     **/
    public final int getWidth() {
	return width;
    }

    /**
     * Gets the current height of this layer, in pixels.
     * @return the height in pixels
     * @see #getWidth
     *
     **/
    public final int getHeight() {
	return height;
    }

    /**
     * Sets the visibility of this Layer.  A visible Layer is rendered when
     * its {@link #paint(Graphics)} method is called; an invisible Layer is
     * not rendered.
     * @param visible <code>true</code> to make the <code>Layer</code> visible, 
     * <code>false</code> to make it invisible
     * @see #isVisible
     *
     */
    public void setVisible(boolean visible) {
        this.visible = visible;
    }

    /**
     * Gets the visibility of this Layer.
     * @return <code>true</code> if the <code>Layer</code> is visible,
     * <code>false</code> if it is invisible.
     * @see #setVisible
     *
     */
    public final boolean isVisible() {
        return visible;
    }

    /**
     * Paints this Layer if it is visible.  The upper-left corner of the Layer
     * is rendered at it's current (x,y) position relative to the origin of
     * the provided Graphics object.  Applications may make use of Graphics
     * clipping and translation to control where the Layer is rendered and to
     * limit the region that is rendered.
     * <P>
     * Implementations of this method are responsible for checking if this
     * Layer is visible; this method does nothing if the Layer is not
     * visible.
     * <p>
     * The attributes of the Graphics object (clip region, translation, 
     * drawing color, etc.) are not modified as a result of calling this
     * method.
     *
     * @param g the graphics object for rendering the <code>Layer</code>
     * @throws NullPointerException if <code>g</code> is <code>null</code>
     */
    public abstract void paint(Graphics g);

    /**
     * Sets the current width of this layer, in pixels.  The Layer's width is
     * used to determine its bounds for rendering purposes.
     * @param width The width in pixels
     * @throws IllegalArgumentException if the specified width is less than 0
     * @see #setHeightImpl
     * @see #getHeight
     * @see #getWidth
     *
     **/
    void setWidthImpl(int width) { 
        if (width < 0) {
            throw new IllegalArgumentException();
        }
        this.width = width;
    }


    /**
     * Sets the current height of this layer, in pixels.  The Layer's height
     * is used to determine its bounds for rendering purposes.
     * @param height The height in pixels
     * @throws IllegalArgumentException if the specified height is less than 0
     * @see #setWidthImpl
     * @see #getHeight
     * @see #getWidth
     *
     **/
    void setHeightImpl(int height) {
        if (height < 0) {
            throw new IllegalArgumentException();
        }
        this.height = height;
    }

    /**
     * position of layer in x offset 
     */
    int x; // = 0;

    /**
     * position of layer in y offset 
     */
    int y; // = 0;

    /**
     * width of layer 
     */
    int width; // = 0;

    /**
     * height of layer
     */
    int height; // = 0;

    /** 
     * If the Layer is visible it will be drawn when <code>paint</code>
     * is called.
     */
    boolean visible = true;

}