CODEWITHSUNDEEP
javaswingawtjava-2d
Toby
Toby

Reputation: 9803

How to fade in graphics.fill call

I'm doing the following to a Canvas object.

graphics.setColor(BLUE);
graphics.fill(new Rectangle2D.Double(x, y, width, height));

I'd like to fade in the fill colour to create a smooth transition from the canvas background colour to the new colour (and possibly fade out whatever colour was originally there).

I've played with this kind of thing (setting the graphics object's composite to an AlphaComposite which a Timer updating the alpha value every n milliseconds) but I get flickering.

I'm wondering what general concept I'm missing.

Thanks for any pointers.

Upvotes: 1

Views: 121

Answers (2)

Dariusz
Dariusz

Reputation: 22311

Your application does exactly what you tell it to do. If you want to make a fade-in effect, you have to determine what kind of color changes you want to make, create a function which does it, and implement the fade itself.

I'd approach it like that:

class FadeEffect{

  int totalDurationMs;

  int elapsedDurationMs;

  Color initialColor;

  Color finalColor;

  Color getColor(int durationDelta) {
    elapsedDurationMs += durationDelta;
    if (elapsedDurationMs > totalDurationMs) {
      return finalColor;
    }
    double progress = 1.0d*elapsedDurationMs/totalDurationMs;
    return new Color( (int)(finalColor.getRed()-initialColor.getRed())*progress,
                      (int)(finalColor.getGreen()-initialColor.getGreen())*progress,
                      (int)(finalColor.getBlue()-initialColor.getBlue())*progress);
  }

  //getters, setters, etc
}

As for the flickering issue: make sure you are using double buffering - either in your component, or by manually drawing on a off-screen buffer (image) and only posting the image to the screen when the drawing is complete.

Here is a sample code from my Graphic2D app doing the double buffering:

private VolatileImage vImg;

@Override
public void paint(Graphics g) {
    if (gc==null) gc = this.getGraphicsConfiguration();
    do {
        boolean sizeChanged = false;
        sizeChanged = (vImg!=null&&(vImg.getWidth()!=getWidth()|| vImg.getHeight()!=getHeight()));
        if (vImg == null || vImg.validate(gc) == VolatileImage.IMAGE_INCOMPATIBLE
                || sizeChanged) {
            vImg = gc.createCompatibleVolatileImage(getWidth(), getHeight());
            vImg.setAccelerationPriority(1);
        }
        final Graphics gimg =  vImg.getGraphics();
        if (gimg instanceof Graphics2D) {
            renderContents((Graphics2D) gimg);
            gimg.dispose();
            g.drawImage(vImg, 0, 0, null);
        } else {
            throw new UnsupportedOperationException("Rendering impossible, graphics are not of Graphics2D class");
        }
    } while (vImg.contentsLost());
    updateAnimationNo();
}

Upvotes: 0

tbodt
tbodt

Reputation: 17017

First of all, how could you be using the AWT? It is quite outdated. I reccomend you switch to swing, mainly because swing has double buffering, which would remove your flicker.

Upvotes: 1

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