Java help: overlapping rectangles that paint a new color where the rectangles overlap

Question

So I'm working on a Java assignment where I had to create a Rectangle class that was utilized in a program that draws overlapping rectangles and where the rectangles overlap, a new rectangle is drawn, with a new color. I have included a link to the HW description as I figured it be easiest to just let you look over that than me trying to explain it..http://myslu.stlawu.edu/~ltorrey/courses/spring13/cs219/hw/hw6.html

I am currently stuck on creating the getOverlap method, which draws the new overlapped rectangle. I had to create a draw method that obviously draws the rectangles and am confused on whether the getOverlap method defines new parameters for the variables that were previously defined and then reroute into the draw method? Any help would be greatly appreciated.

This lacks any clear question. Voting to close as 'not a real question'. — Andrew Thompson, Mar 20 '13 at 03:27
Can you use the `intersection()` method of `java.awt.Rectangle`? — trashgod, Mar 20 '13 at 03:35
@trashgod, I missed your comment as I was concentrating on MadProgrammers code. Yes, that would be the easiest approach. — camickr, Mar 20 '13 at 04:39
@camickr: I outlined the approach below thinking that user2189162 had responded, but I left the fun part as an exercise. More `Area` [here](http://stackoverflow.com/q/9526835/230513). — trashgod, Mar 20 '13 at 05:01

score 5 · Answer 1 · answered Mar 20 '13 at 03:36

With a little clever use of Area you can get the Graphics2D API to do it for you.

Basically, I create an Area that is the result of an exclusiveOR operation on the two rectangles. I then subtract this from an Area that is the result of adding the two rectangles together

enter image description here

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.Area;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class OverlappingRectangles {

    public static void main(String[] args) {
        new OverlappingRectangles();
    }

    public OverlappingRectangles() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            Rectangle r1 = new Rectangle(0, 0, 150, 150);
            Rectangle r2 = new Rectangle(50, 50, 150, 150);

            g2d.setColor(Color.RED);
            g2d.fill(r1);
            g2d.setColor(Color.BLUE);
            g2d.fill(r2);

            Area a1 = new Area(r1);
            a1.exclusiveOr(new Area(r2));
            Area a2 = new Area(r2);
            a2.add(new Area(r1));
            a2.subtract(a1);

            g2d.setColor(Color.GREEN);
            g2d.fill(a2);

            g2d.dispose();
        }
    }

}

+1 for `Area`; I was looking at `java.awt.Rectangle`, but I stopped to practice re-factoring in my IDE. — trashgod, Mar 20 '13 at 03:49
@trashgod Had to rip myself away from implementing draggable column groups in table header... — MadProgrammer, Mar 20 '13 at 03:51
+1, cool. I was looking at the Shape API over the weekend wondering when you might use an Area. Nice example, although it can be simplified even more. See my findings. — camickr, Mar 20 '13 at 04:31

score 3 · Answer 2 · answered Mar 20 '13 at 04:30

3

Playing with MadProgrammer's code I found a couple of simpler ways to do this:

Using an Area:

Area yellow = new Area(r1);
yellow.intersect( new Area(r2) );
g2d.setColor(Color.YELLOW);
g2d.fill(yellow);

Or using another Rectangle:

Rectangle green = r1.intersection(r2);
g2d.setColor(Color.GREEN);
g2d.fill(green);

answered Mar 20 '13 at 04:30

camickr

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*pulls hair out* I've been looking for away to do that for ages!! – MadProgrammer Mar 20 '13 at 04:33

score 2 · Answer 3 · answered Mar 20 '13 at 04:52

If java.awt.Rectangle is permitted, here's an outline of how you can use it in your implementation:

private static class Rectangle {
    private int x1, y1, x2, y2, r, g, b;
    private java.awt.Rectangle r1 = new java.awt.Rectangle();
    private java.awt.Rectangle r2 = new java.awt.Rectangle();
    private java.awt.Rectangle r3;

    public Rectangle(int x1, int y1, int x2, int y2, int r, int g, int b) {
        ...
    }

    private void draw(Graphics page) {
        ...
    }

    private boolean overlapsWith(Rectangle r) {
        r1.setBounds(...);
        r2.setBounds(...);
        return r1.intersects(r2);
    }

    private Rectangle getOverlap(Rectangle r) {
        r1.setBounds(...);
        r2.setBounds(...);
        r3 = r1.intersection(r2);
        return new Rectangle(...);
    }

Java help: overlapping rectangles that paint a new color where the rectangles overlap

3 Answers3

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