Draw transparent rectangles with mouse - Java 2D Graphics

Java examples for 2D Graphics:Paint

  1. HOME
  2. Java
  3. 2D Graphics
  4. Paint

Description

Draw transparent rectangles with mouse

Demo Code

import java.awt.AlphaComposite;
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.geom.Line2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;

import javax.swing.JComponent;
import javax.swing.JFrame;

public class Main extends JFrame {

  public static void main(String[] args) {
    new Main();//from  w w w  .j a va  2s .c  o  m
  }

  public Main() {
    this.setSize(300, 300);
    this.setTitle("The Drawing Board");
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.add(new PaintSurface(), BorderLayout.CENTER);
    this.setVisible(true);
  }

}

class PaintSurface extends JComponent {
  ArrayList<Shape> shapes = new ArrayList<Shape>();
  Point startDrag, endDrag;

  public PaintSurface() {
    this.addMouseListener(new MouseAdapter() {
      public void mousePressed(MouseEvent e) {
        startDrag = new Point(e.getX(), e.getY());
        endDrag = startDrag;
        repaint();
      }

      public void mouseReleased(MouseEvent e) {
        Shape r = makeRectangle(startDrag.x, startDrag.y, e.getX(), e.getY());
        shapes.add(r);
        startDrag = null;
        endDrag = null;
        repaint();
      }
    });

    this.addMouseMotionListener(new MouseMotionAdapter() {
      public void mouseDragged(MouseEvent e) {
        endDrag = new Point(e.getX(), e.getY());
        repaint();
      }
    });
  }

  public void paint(Graphics g) {
    Graphics2D g2 = (Graphics2D) g;

    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

    // draw background grid
    g2.setPaint(Color.LIGHT_GRAY);
    for (int i = 0; i < getSize().width; i += 10) {
      Shape line = new Line2D.Float(i, 0, i, getSize().height);
      g2.draw(line);
    }

    for (int i = 0; i < getSize().height; i += 10) {
      Shape line = new Line2D.Float(0, i, getSize().width, i);
      g2.draw(line);
    }

    // draw the shapes
    Color[] colors = { Color.RED, Color.BLUE, Color.PINK, Color.YELLOW, Color.MAGENTA, Color.CYAN };
    int colorIndex = 0;

    g2.setStroke(new BasicStroke(2));
    g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.50f));

    for (Shape s : shapes) {
      g2.setPaint(Color.BLACK);
      g2.draw(s);
      g2.setPaint(colors[(colorIndex++) % 6]);
      g2.fill(s);
    }

    // paint the temporary rectangle
    if (startDrag != null && endDrag != null) {
      g2.setPaint(Color.LIGHT_GRAY);
      Shape r = makeRectangle(startDrag.x, startDrag.y, endDrag.x, endDrag.y);
      g2.draw(r);
    }
  }

  private Rectangle2D.Float makeRectangle(int x1, int y1, int x2, int y2) {
    int x = Math.min(x1, x2);
    int y = Math.min(y1, y2);
    int width = Math.abs(x1 - x2);
    int height = Math.abs(y1 - y2);

    return new Rectangle2D.Float(x, y, width, height);
  }
}

Related Tutorials