在SWT中用这种方式重画的动态图片，为什么设定不了图片的背景颜色呢？

在SWT中插入的动态等待图片，设定的dg背景色，画的时候无效，这是为什么呢？求高手相助~**

package test;

import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.ImageData;
import org.eclipse.swt.graphics.ImageLoader;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.Shell;

public class ImageViewers extends Canvas {

protected Point origin = new Point(0, 0);
protected Image image;
protected ImageData[] imageDatas;
protected Image[] images;
protected int current;

private int repeatCount;
private Runnable animationTimer;
private Color bg;
private Display display;

public ImageViewers(Composite parent) {
    super(parent, SWT.NO_BACKGROUND);

    bg = new Color(null, 248, 85, 40);
    display = getDisplay();
    addListeners();
}

/**
 * @param repeatCount
 *            0 forever
 */
public void setImages(ImageData[] imageDatas, int repeatCount) {
    checkWidget();

    this.image = null;
    this.imageDatas = imageDatas;
    this.repeatCount = repeatCount;
    convertImageDatasToImages();
    startAnimationTimer();
    redraw();
}

@Override
public Point computeSize(int wHint, int hHint, boolean changed) {
    checkWidget();

    Image image = getCurrentImage();
    if (image != null) {
        Rectangle rect = image.getBounds();
        Rectangle trim = computeTrim(0, 0, rect.width, rect.height);
        return new Point(trim.width, trim.height);
    }

    return new Point(wHint, hHint);
}

@Override
public void dispose() {
    if (image != null)
        image.dispose();

    if (images != null)
        for (int i = 0; i < images.length; i++)
            images[i].dispose();

    super.dispose();
}

protected void paint(Event e) {
    Image image = getCurrentImage();
    if (image == null)
        return;

    GC gc = e.gc;
    gc.drawImage(image, origin.x, origin.y);

    gc.setBackground(bg);
    Rectangle rect = image.getBounds();
    Rectangle client = getClientArea();
    int marginWidth = client.width - rect.width;
    if (marginWidth > 0) {
        gc.fillRectangle(rect.width, 0, marginWidth, client.height);
    }
    int marginHeight = client.height - rect.height;
    if (marginHeight > 0) {
        gc.fillRectangle(0, rect.height, client.width, marginHeight);
    }
}

void addListeners() {
    addListener(SWT.Paint, new Listener() {
        public void handleEvent(Event e) {
            paint(e);
        }
    });
}

void convertImageDatasToImages() {
    images = new Image[imageDatas.length];

    // Step 1: Determine the size of the resulting images.
    int width = imageDatas[0].width;
    int height = imageDatas[0].height;

    // Step 2: Construct each image.
    int transition = SWT.DM_FILL_BACKGROUND;
    for (int i = 0; i < imageDatas.length; i++) {
        ImageData id = imageDatas[i];
        images[i] = new Image(display, width, height);
        GC gc = new GC(images[i]);

        // Do the transition from the previous image.
        switch (transition) {
        case SWT.DM_FILL_NONE:
        case SWT.DM_UNSPECIFIED:
            // Start from last image.
            gc.drawImage(images[i - 1], 0, 0);
            break;
        case SWT.DM_FILL_PREVIOUS:
            // Start from second last image.
            gc.drawImage(images[i - 2], 0, 0);
            break;
        default:
            // DM_FILL_BACKGROUND or anything else,
            // just fill with default background.
            gc.setBackground(bg);
            gc.fillRectangle(0, 0, width, height);
            break;
        }

        // Draw the current image and clean up.
        Image img = new Image(display, id);
        gc.drawImage(img, 0, 0, id.width, id.height, id.x, id.y, id.width,
                id.height);
        img.dispose();
        gc.dispose();

        // Compute the next transition.
        // Special case: Can't do DM_FILL_PREVIOUS on the
        // second image since there is no "second last"
        // image to use.
        transition = id.disposalMethod;
        if (i == 0 && transition == SWT.DM_FILL_PREVIOUS)
            transition = SWT.DM_FILL_NONE;
    }
}

Image getCurrentImage() {
    if (image != null)
        return image;

    if (images == null)
        return null;

    return images[current];
}

void startAnimationTimer() {
    if (images == null || images.length < 2)
        return;

    final int delay = imageDatas[current].delayTime * 10;
    display.timerExec(delay, animationTimer = new Runnable() {
        public void run() {
            if (isDisposed())
                return;

            current = (current + 1) % images.length;
            redraw();

            if (current + 1 == images.length && repeatCount != 0
                    && --repeatCount <= 0)
                return;
            display.timerExec(delay, this);
        }
    });
}

void stopAnimationTimer() {
    if (animationTimer != null)
        display.timerExec(-1, animationTimer);
}

public static void main(String[] args) {
    Display display = new Display();
    final Shell shell = new Shell(display);
    ImageViewers ic = new ImageViewers(shell);

    shell.setSize(500, 300);

    ImageLoader loader = new ImageLoader();
    ImageData[] imageDatas = loader.load("E:/image/11.gif");
    ic.setImages(imageDatas, loader.repeatCount);

    ic.pack();
    shell.open();
    while (!shell.isDisposed()) {
        if (!display.readAndDispatch())
            display.sleep();
    }
    display.dispose();
}

}

有大神帮忙吗~求助！！！

http://blog.csdn.net/cuiran/article/details/7339936