Drawing an image using sub-pixel level accuracy using Graphics2D

Question

I am currently attempting to draw images on the screen at a regular rate like in a video game.

Unfortunately, because of the rate at which the image is moving, some frames are identical because the image has not yet moved a full pixel.

Is there a way to provide float values to Graphics2D for on-screen position to draw the image, rather than int values?

Initially here is what I had done:

BufferedImage srcImage = sprite.getImage ( );
Position imagePosition = ... ; //Defined elsewhere
g.drawImage ( srcImage, (int) imagePosition.getX(), (int) imagePosition.getY() );

This of course thresholds, so the picture doesn't move between pixels, but skips from one to the next.

The next method was to set the paint color to a texture instead and draw at a specified position. Unfortunately, this produced incorrect results that showed tiling rather than correct antialiasing.

g.setRenderingHint ( RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON );

BufferedImage srcImage = sprite.getImage ( );

g.setPaint ( new TexturePaint ( srcImage, new Rectangle2D.Float ( 0, 0, srcImage.getWidth ( ), srcImage.getHeight ( ) ) ) );

AffineTransform xform = new AffineTransform ( );

xform.setToIdentity ( );
xform.translate ( onScreenPos.getX ( ), onScreenPos.getY ( ) );
g.transform ( xform );

g.fillRect(0, 0, srcImage.getWidth(), srcImage.getHeight());

What should I do to achieve the desired effect of subpixel rendering of an Image in Java?

Answer 1

You can use a BufferedImage and AffineTransform, draw to the buffered image, then draw the buffered image to the component in the paint event.

    /* overrides the paint method */
    @Override
    public void paint(Graphics g) {
        /* clear scene buffer */
        g2d.clearRect(0, 0, (int)width, (int)height);

        /* draw ball image to the memory image with transformed x/y double values */
        AffineTransform t = new AffineTransform();
        t.translate(ball.x, ball.y); // x/y set here, ball.x/y = double, ie: 10.33
        t.scale(1, 1); // scale = 1 
        g2d.drawImage(image, t, null);

        // draw the scene (double percision image) to the ui component
        g.drawImage(scene, 0, 0, this);
    }

Check my full example here: http://pastebin.com/hSAkYWqM