如何在JFrame中创建独立的JPanel-Layers并分别重新绘制每个图层

Question

I'm searching for a way to paint several JComponents above each other (overlap) and still being able to individually access and alter them.

Eg paint three JPanels with transparent backgrounds - each containing a circle, a rectangle or a line. Afterwards, I'd like to change the appearance of the circle. The other two should not be repainted (similarly to layers in Photoshop).

My current project has a Jpanel with thousands of lines and I need to change a rectangle in the back on mouseover if I redraw the complete Jpanel each time it is very laggy.

Is there a decent way to accomplish that? Thank you already for your ideas!

Answer 1

I need to change a rectangle in the back

You can invoke:

panel.repaint(rectangle); // or 
panel.repaint(x, y, width, height);

to specify the Rectangular area to be repainted.

Answer 2

It worked quite fine - here is my code if anyone else has a similar problem! the first image can be stored and displayed later on (buff) Make sure to generate new BufferedImage (here canvas) when displaying again, as the transperency is lost otherways. Thanks to Gilbert Le Blanc

@Override
protected void paintComponent(Graphics g1) {
    //Create image:
    BufferedImage buff = new BufferedImage(mywidth, myheight, BufferedImage.TYPE_INT_ARGB);

    //write to image:
    Graphics2D g2 = (Graphics2D) buff.getGraphics();
    g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER,(float) 0.01f));
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2.draw(xxxRectanglewhatever);

    //then - later draw image again
    BufferedImage canvas = new BufferedImage(mywidth, myheight, BufferedImage.TYPE_INT_ARGB);
    canvas.getGraphics().drawImage(buff, 0, 0, null);
    ((Graphics2D) g1).setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
    g1.drawImage(canvas, 0, 0, null);
    canvas.flush();
}