Question

I am basically trying to do something like classic “Paint” (Microsoft’s program). But i want to work with layers when painting. I thought i can use JPanel component as layer.

I was testing the code below. The goal is drawing a rectangle with mouse. There is a temp layer (temp) to draw on it while dragging the mouse, and there is actual layer (area) to draw when mouse released. But every time i start drawing a new rectangle, old ones are disappear. Also if i execute setVisible(false) and true again, everything disappears.

MouseInputAdapter mia = new MouseInputAdapter() {
    private int startx = 0, starty = 0, stopx = 0, stopy = 0;

    public void mousePressed(MouseEvent evt) {
        startx = evt.getX();
        starty = evt.getY();
    }

    public void mouseDragged(MouseEvent evt) {
        Graphics2D tempg = (Graphics2D) temp.getGraphics();

        int width = Math.abs(startx - evt.getX());
        int height = Math.abs(starty - evt.getY());
        int x = evt.getX(), y = evt.getY();
        if(x > startx)
            x = startx;
        if(y > starty)
            y = starty;

        Rectangle r = new Rectangle(x, y, width, height); 
        tempg.clearRect(0, 0, getWidth(), getHeight());
        tempg.draw(r);
    }

    public void mouseReleased(MouseEvent evt) {
        Graphics2D g = (Graphics2D) area.getGraphics();
        stopx = evt.getX();
        stopy = evt.getY();

        int width = Math.abs(startx - stopx);
        int height = Math.abs(starty - stopy);
        int x = startx, y = starty;
        if(x > stopx)
            x = stopx;
        if(y > stopy)
            y = stopy;

        Rectangle r = new Rectangle(x, y, width, height);
        g.draw(r);
    }
};
area.addMouseListener(mia);
area.addMouseMotionListener(mia);
temp.addMouseListener(mia);
temp.addMouseMotionListener(mia);

What is wrong with that code?

Answer 1

This is what i was looking for; http://www.leepoint.net/notes-java/examples/mouse/paintdemo.html

My mistake; using getGraphics() method out of paintComponent() and expecting keep changes.

Why @Keilly’s answer not working for me; Because if i put shapes in a list or array, when a shape changed (for example; deleting a circle’s 1/4) i can’t update the element in the list. Because it doesn’t be same shape anymore. So i have to keep shapes as drawings, and i don’t have to (and dont want to) keep them separately.