摆动问题：在pdf图像上绘制矩形，并在放大和缩小时保持其大小和位置一致

Question

I have a rather pressing question in regards to Swing, which I haven't touched for many years.

I have a code that allows the user to draw different rectangles on the pdf document (contained within JPanel ). I draw them, move them, resize them, select them, and even write text on them. What I can't do is to keep them consistent when I zoom the document. As the document gets bigger, the rectangles I've drawn stay at the same position and the same size.

I was wondering if there's a relatively easy logic to track the zooming level and, most importantly, update the rectangles accordingly. I can retrieve zoom factor, it's a float, but, unfortunately, I'm using Rectangle object, which uses int for x , y , height , and width . It will be a hassle to convert it to Rectangle.Float , and I wanted to save it for a last resort.

I've tried to use AffineTransform , but I'm not quite familiar with it, for some reason I'm getting the wrong coordinates for y . Can anyone explain to me:

1. What's the best way to control the Rectangle object, as the pdf document gets zoomed in and out?
2. If AffineTransform is the best way, how should I handle it (maybe there's a link to a good explanation, if so - I couldn't find it)?

This is the only issue I've been struggling with and it's getting a bit frustrating now.

Answer 1

To scale using an AffineTransform :

1. Get the transform T of the Graphics object G
2. Create an AffineTransform object A
3. Set the scale of A
4. Set the transform of the G to A
5. Draw the shapes
6. Set the transform of G back to T

Translated into code - assuming scale is the value to scale by:

@Override
protected void paintComponent(Graphics gr){
    super.paintComponent(gr);
    Graphics2D g = (Graphics2D)gr;
    AffineTransform prevTransform = g.getTransform();
    AffineTransform at = new AffineTransform(prevTransform);
    at.scale(scale, scale); 
    g.setTransform(at);
    g.drawRect(...);
    g.setTransform(prevTransform); 
}