gamecanvas.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]

     * <P>The newly created Graphics object has the following properties:
     * </P>
     * <ul>
     * <LI>the destination is this GameCanvas' buffer;
     * <LI>the clip region encompasses the entire buffer;
     * <LI>the current color is black;
     * <LI>the font is the same as the font returned by
     * {@link javax.microedition.lcdui.Font#getDefaultFont 
     * Font.getDefaultFont()};
     * <LI>the stroke style is {@link Graphics#SOLID SOLID}; and
     * <LI>the origin of the coordinate system is located at the upper-left
     * corner of the buffer.
     * </ul>     
     * <p>
     * @return the Graphics object that renders to this GameCanvas' 
     * off-screen buffer
     * @see #flushGraphics()
     * @see #flushGraphics(int, int, int, int)	 
     */
    protected Graphics getGraphics() {
	return offscreen_buffer.getGraphics();
    }

    /**
     * Gets the states of the physical game keys.  Each bit in the returned
     * integer represents a specific key on the device.  A key's bit will be
     * 1 if the key is currently down or has been pressed at least once since
     * the last time this method was called.  The bit will be 0 if the key
     * is currently up and has not been pressed at all since the last time 
     * this method was called.  This latching behavior ensures that a rapid
     * key press and release will always be caught by the game loop, 
     * regardless of how slowly the loop runs.
     * <p>
     * For example:<code><pre>
     * 
     *      // Get the key state and store it
     *      int keyState = getKeyStates();
     *      if ((keyState & LEFT_KEY) != 0) {
     *          positionX--;
     *      }
     *      else if ((keyState & RIGHT_KEY) != 0) {
     *          positionX++;
     *      }
     *
     * </pre></code>
     * <p>
     * Calling this method has the side effect of clearing any latched state.
     * Another call to getKeyStates immediately after a prior call will 
     * therefore report the system's best idea of the current state of the
     * keys, the latched bits having been cleared by the first call.
     * <p>
     * Some devices may not be able to query the keypad hardware directly and
     * therefore, this method may be implemented by monitoring key press and
     * release events instead.  Thus the state reported by getKeyStates might
     * lag the actual state of the physical keys since the timeliness
     * of the key information is be subject to the capabilities of each
     * device.  Also, some devices may be incapable of detecting simultaneous
     * presses of multiple keys.
     * <p>
     * This method returns 0 unless the GameCanvas is currently visible as
     * reported by {@link javax.microedition.lcdui.Displayable#isShown}.
     * Upon becoming visible, a GameCanvas will initially indicate that 
     * all keys are unpressed (0); if a key is held down while the GameCanvas
     * is being shown, the key must be first released and then pressed in 
     * order for the key press to be reported by the GameCanvas.
     * <p>
     * @see #UP_PRESSED
     * @see #DOWN_PRESSED
     * @see #LEFT_PRESSED
     * @see #RIGHT_PRESSED
     * @see #FIRE_PRESSED
     * @see #GAME_A_PRESSED
     * @see #GAME_B_PRESSED
     * @see #GAME_C_PRESSED
     * @see #GAME_D_PRESSED
     * @return An integer containing the key state information (one bit per 
     * key), or 0 if the GameCanvas is not currently shown.
     */
    public int getKeyStates() {
        DisplayAccess displayAccess = GameMap.get(this);
	if (displayAccess != null) {
	    return displayAccess.getKeyMask();
	} 
	return 0;
    }

    /**
     * Paints this GameCanvas.  By default, this method renders the 
     * the off-screen buffer at (0,0).  Rendering of the buffer is 
     * subject to the clip region and origin translation of the Graphics
     * object.
     * @param g the Graphics object with which to render the screen.
     * @throws NullPointerException if <code>g</code> is <code>null</code>
     */
    public void paint(Graphics g) {
        // NullPointerException will be thrown in drawImage if g == null
	g.drawImage(offscreen_buffer, 0, 0, Graphics.TOP|Graphics.LEFT);
    }

    /**
     * Flushes the specified region of the off-screen buffer to the display. 
     * The contents of the off-screen buffer are not changed as a result of 
     * the flush operation.  This method does not return until the flush has
     * been completed, so the app may immediately begin to render the next 
     * frame to the same buffer once this method returns.
     * <p>
     * If the specified region extends beyond the current bounds of the 
     * GameCanvas, only the intersecting region is flushed.  No pixels are
     * flushed if the specified width or height is less than 1.
     * <p>
     * This method does nothing and returns immediately if the GameCanvas is
     * not currently shown or the flush request cannot be honored because the
     * system is busy.
     * <p>
     * @see #flushGraphics()
     * @param x the left edge of the region to be flushed 
     * @param y the top edge of the region to be flushed
     * @param width the width of the region to be flushed
     * @param height the height of the region to be flushed
     */
    public void flushGraphics(int x, int y, 
    					int width, int height) {
	if (width < 1 || height < 1) {
	    return;
	}

        DisplayAccess displayAccess = GameMap.get(this);
        if (displayAccess != null) {
            displayAccess.flush(this, offscreen_buffer, 
    			  x, y,	width, height);
        }
    }

    /**
     * Flushes the off-screen buffer to the display.  The size of the flushed 
     * area is equal to the size of the GameCanvas.  The contents
     * of the  off-screen buffer are not changed as a result of the flush 
     * operation.  This method does not return until the flush has been
     * completed, so the app may immediately begin to render the next frame
     * to the same buffer once this method returns.
     * <p>
     * This method does nothing and returns immediately if the GameCanvas is
     * not currently shown or the flush request cannot be honored because the
     * system is busy.
     * <p>
     * @see #flushGraphics(int,int,int,int)	  
     */
    public void flushGraphics() {

        DisplayAccess displayAccess = GameMap.get(this);
        if (displayAccess != null) {
	    displayAccess.flush(this, offscreen_buffer,
			      0, 0, getWidth(), getHeight());
        }
    }

    /**
     * Set a private field in the <code>Canvas</code> object. We use a
     * native method to work around the package boundary.
     * @param c this <code>GameCanvas</code> cast to a <code>Canvas</code>
     * @param suppressKeyEvents whether or not to suppress key events
     */
    private native void setSuppressKeyEvents(Canvas c, 
					     boolean suppressKeyEvents);

    static {
	// do this to get the HEIGHT available to draw on in full screen mode.
        GameDeviceCaps gdc = new GameDeviceCaps();

        FULLSCREEN_WIDTH    = gdc.width;
        FULLSCREEN_HEIGHT   = gdc.height;

        gdc = null;
    }
}

/*
 * ************* Class, DeviceCaps
 */

/**
 * Current device capabilities.
 * Can't access Display's DeviceCaps. So make game's own.
 *
 */
class GameDeviceCaps {
    /** horizontal width of the current device */
    int width;

    /** vertical height of the current device */
    int height;

    /** 
     * Create a new GameDeviceCaps object that retrieves
     * the devices capabilities
     */
    GameDeviceCaps() {
        init();
    }

    /** 
     * native method to retreive initial settings for
     * display capabilities
     */
    private native void init();
}