Good practice for drawing and zooming image?

Question

I have a JScrollPane with a JPanel where I can draw by mouse and code. I need the possibility to zoom on details in my drawing. But soon I get a outOfMemoryError. I think because I make my drawing to big while zooming. This is my code:

    private BufferedImage _bufferedImage;
private int _panelWidth = 2000, _panelHeight = 1500;

@Override
public void paintComponent(Graphics g){
    super.paintComponent(g);
    if(_bufferedImage != null){
        g.drawImage(_bufferedImage, 0, 0, this);
    }
}

public void draw(float zoomFactor){
    try {
        int width = (int)(_panelWidth * zoomFactor);
        int height = (int)(_panelHeight * zoomFactor);
        _bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        Graphics2D g2 = _bufferedImage.createGraphics();
        g2.setBackground(Color.WHITE);
        g2.setPaint(Color.BLACK);
        g2.scale(zoomFactor, zoomFactor);
        drawHouse(g2); ...
        g2.dispose();
    } 
    catch (Exception e) {
        e.printStackTrace();
    }
    repaint();
}

There must be better practice then what I did.

I can just draw the area of the scrollpane, but then I can't use the scrollbars, then I have to use buttons with arrow up, right, left, down to scroll in my drawing. Anyone who can me give a hint?

1) For better help sooner, post an [SSCCE](http://sscce.org/). 2) One way to get image(s) for an example is to hot-link to the images seen in [this answer](http://stackoverflow.com/a/19209651/418556). — Andrew Thompson, Dec 13 '13 at 20:41

score 2 · Answer 1 · answered Dec 13 '13 at 20:50

but then I can't use the scrollbars

Scrollbars work when the preferred size of the component is greater than the size of the scrollpane. If you are zooming the image in the paintComponent() method then you would also need to override the getPreferredSize() method to return the appropriate size of the image that takes into account the zooming factor.

So in your case the preferred size would be the size of your image.

score 2 · Answer 2 · edited May 23 '17 at 10:25

2

If you want to zoom in, I am assuming you are no trying to make "bigger pixels", but to draw the same figures at a higher scale. In that case, you should not be using a BufferedImage at all -- instead, you should draw to a suitably scaled JPanel or similar. You can always take a snapshot of whatever you are rendering whenever you need it; but rendering to a BufferedImage without need is wasteful (of time and memory).

See this answer for details.

edited May 23 '17 at 10:25

Community

1
1

answered Dec 13 '13 at 22:32

tucuxi

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Thank you for the example (FPanel), it looks promising. I try to implement it. The reason why I thought I need a BufferedImage, is becease I draw lines with the mouse by dragging. I have to draw the drag-lines and to delete the previous when the cursor moves. Also there are a lot of calculations to do for the drawing. I tried to avoid to redo thes calculations with each repaint. – Jan Van den Bossche Dec 15 '13 at 13:30
I think it will do it very good. obviously I don't need the buffered image. Thanks. – Jan Van den Bossche Dec 17 '13 at 18:11

Good practice for drawing and zooming image?

2 Answers2