Painting in Swing

Swing's painting system is able to render vector graphics, images, and outline font-based text.

Painting is needed in applications when we want to change or enhance an existing widget, or if we are creating a custom widget from scratch To do the painting, we use the painting API provided by the Swing toolkit.

The painting is done within the paintComponent() method. In the painting process, we use the Graphics2D object.

2D Vector Graphics

There are two different computer graphics. Vector and raster graphics. Raster graphics represents images as a collection of pixels. Vector graphics is the use of geometrical primitives such as points, lines, curves or polygons to represent images. These primitives are created using mathematical equations.

Both types of computer graphics have advantages and disadvantages. The advantages of vector graphics over raster are:

Types of primitives

Points

The most simple graphics primitive is point. It is a single dot on the window. There is no method to draw a point in Swing. To draw a point, we use the drawLine() method. We use one point twice.

PointsEx.java
package com.zetcode;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawPanel extends JPanel {

    private void doDrawing(Graphics g) {

        Graphics2D g2d = (Graphics2D) g;

        g2d.setColor(Color.blue);

        for (int i = 0; i <= 1000; i++) {

            Dimension size = getSize();
            Insets insets = getInsets();

            int w = size.width - insets.left - insets.right;
            int h = size.height - insets.top - insets.bottom;

            Random r = new Random();
            int x = Math.abs(r.nextInt()) % w;
            int y = Math.abs(r.nextInt()) % h;
            g2d.drawLine(x, y, x, y);
        }
    }

    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);
        doDrawing(g);
    }
}

public class PointsEx extends JFrame {

    public PointsEx() {
        
        initUI();
    }

    private void initUI() {

        DrawPanel dpnl = new DrawPanel();
        add(dpnl);

        setSize(350, 250);
        setTitle("Points");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            PointsEx ex = new PointsEx();
            ex.setVisible(true);
        });
    }
}

One point is difficult to observe. Therefore, we will randomly draw 1000 points on the panel surface.

class DrawPanel extends JPanel {

We are drawing on a custom drawing panel, which is a JPanel component. The drawing panel will later be added to a JFrame component.

@Override
public void paintComponent(Graphics g) {
    
    super.paintComponent(g);
    doDrawing(g);
}

Custom painting is performed inside the paintComponent() method, which we override. The super.paintComponent() method calls the method of the parent class. It does some necessary work to prepare component for drawing. Actual drawing is delegated to the doDrawing() method.

Graphics2D g2d = (Graphics2D) g;

Painting in Swing is done on the Graphics2D object.

g2d.setColor(Color.blue);

We will paint our points in blue colour.

Dimension size = getSize();
Insets insets = getInsets();

The size of the window includes borders and titlebar. We do not paint there.

int w =  size.width - insets.left - insets.right;
int h =  size.height - insets.top - insets.bottom;

Here we calculate the area, where we will effectively paint our points.

Random r = new Random();
int x = Math.abs(r.nextInt()) % w;
int y = Math.abs(r.nextInt()) % h;

We get a random number in range of the size of area that we computed above.

g2d.drawLine(x, y, x, y);

Here we draw the point. As we already said, we use a drawLine() method. We specify the same point twice.

Points
Figure: Points

Lines

A line is a simple graphics primitive. It is drawn using two points.

LinesEx.java
package com.zetcode;

import java.awt.BasicStroke;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawPanel extends JPanel {

    private void doDrawing(Graphics g) {
        
        Graphics2D g2d = (Graphics2D) g;

        float[] dash1 = {2f, 0f, 2f};
        float[] dash2 = {1f, 1f, 1f};
        float[] dash3 = {4f, 0f, 2f};
        float[] dash4 = {4f, 4f, 1f};

        g2d.drawLine(20, 40, 250, 40);

        BasicStroke bs1 = new BasicStroke(1, BasicStroke.CAP_BUTT,
                BasicStroke.JOIN_ROUND, 1.0f, dash1, 2f);

        BasicStroke bs2 = new BasicStroke(1, BasicStroke.CAP_BUTT,
                BasicStroke.JOIN_ROUND, 1.0f, dash2, 2f);

        BasicStroke bs3 = new BasicStroke(1, BasicStroke.CAP_BUTT,
                BasicStroke.JOIN_ROUND, 1.0f, dash3, 2f);

        BasicStroke bs4 = new BasicStroke(1, BasicStroke.CAP_BUTT,
                BasicStroke.JOIN_ROUND, 1.0f, dash4, 2f);

        g2d.setStroke(bs1);
        g2d.drawLine(20, 80, 250, 80);

        g2d.setStroke(bs2);
        g2d.drawLine(20, 120, 250, 120);

        g2d.setStroke(bs3);
        g2d.drawLine(20, 160, 250, 160);

        g2d.setStroke(bs4);
        g2d.drawLine(20, 200, 250, 200);
    }

    @Override
    public void paintComponent(Graphics g) {
        
        super.paintComponent(g);
        doDrawing(g);
    }
}

public class LinesEx extends JFrame {

    public LinesEx() {
        
        initUI();
    }

    private void initUI() {

        DrawPanel dpnl = new DrawPanel();
        add(dpnl);

        setSize(280, 270);
        setTitle("Lines");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            LinesEx ex = new LinesEx();
            ex.setVisible(true);
        });
    }
}

In the example, we draw five lines. The first line is drawn using the default values. Other will have a different stroke. The stroke is created using the BasicStroke class. It defines a basic set of rendering attributes for the outlines of graphics primitives.

float[] dash1 = { 2f, 0f, 2f };

Here we create a dash that we use in the stroke object.

BasicStroke bs1 = new BasicStroke(1, BasicStroke.CAP_BUTT, 
    BasicStroke.JOIN_ROUND, 1.0f, dash1, 2f )

This code creates a stroke. The stroke defines the line width, end caps, line joins, miter limit, dash and the dash phase.

Lines
Figure: Lines

Rectangles

To draw rectangles, we use the drawRect() method. To fill rectangles with the current color, we use the fillRect() method.

RectanglesEx.java
package com.zetcode;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawPanel extends JPanel {

    private void doDrawing(Graphics g) {
        
        Graphics2D g2d = (Graphics2D) g;

        g2d.setColor(new Color(212, 212, 212));
        g2d.drawRect(10, 15, 90, 60);
        g2d.drawRect(130, 15, 90, 60);
        g2d.drawRect(250, 15, 90, 60);
        g2d.drawRect(10, 105, 90, 60);
        g2d.drawRect(130, 105, 90, 60);
        g2d.drawRect(250, 105, 90, 60);
        g2d.drawRect(10, 195, 90, 60);
        g2d.drawRect(130, 195, 90, 60);
        g2d.drawRect(250, 195, 90, 60);

        g2d.setColor(new Color(125, 167, 116));
        g2d.fillRect(10, 15, 90, 60);

        g2d.setColor(new Color(42, 179, 231));
        g2d.fillRect(130, 15, 90, 60);

        g2d.setColor(new Color(70, 67, 123));
        g2d.fillRect(250, 15, 90, 60);

        g2d.setColor(new Color(130, 100, 84));
        g2d.fillRect(10, 105, 90, 60);

        g2d.setColor(new Color(252, 211, 61));
        g2d.fillRect(130, 105, 90, 60);

        g2d.setColor(new Color(241, 98, 69));
        g2d.fillRect(250, 105, 90, 60);

        g2d.setColor(new Color(217, 146, 54));
        g2d.fillRect(10, 195, 90, 60);

        g2d.setColor(new Color(63, 121, 186));
        g2d.fillRect(130, 195, 90, 60);

        g2d.setColor(new Color(31, 21, 1));
        g2d.fillRect(250, 195, 90, 60);
    }

    @Override
    public void paintComponent(Graphics g) {
        
        super.paintComponent(g);
        doDrawing(g);
    }
}

public class RectanglesEx extends JFrame {

    public RectanglesEx() {
        
        initUI();
    }

    private void initUI() {

        DrawPanel dpnl = new DrawPanel();
        add(dpnl);

        setSize(360, 300);
        setTitle("Rectangles");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            RectanglesEx ex = new RectanglesEx();
            ex.setVisible(true);
        });
    }
}

In the example we draw nine coloured rectangles.

g2d.setColor(new Color(212, 212, 212));
g2d.drawRect(10, 15, 90, 60);
...

We set the colour of the outline of the rectangle to a soft gray colour, so that it does not interfere with the fill colour. To draw the outline of the rectangle, we use the drawRect() method. The first two parameters are the x and y values. The third and fourth are width and height.

g2d.fillRect(10, 15, 90, 60);

To fill the rectangle with a colour, we use the fillRect() method.

Rectangles
Figure: Rectangles

Textures

A texture is a bitmap image applied to a shape. To work with textures in Java 2D, we use the TexturePaint class.

TexturesEx.java
package com.zetcode;

import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.TexturePaint;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawingPanel extends JPanel {

    private BufferedImage slate;
    private BufferedImage java;
    private BufferedImage pane;
    private TexturePaint slatetp;
    private TexturePaint javatp;
    private TexturePaint panetp;

    public DrawingPanel() {

        loadImages();
    }

    private void loadImages() {

        try {

            slate = ImageIO.read(new File("slate.png"));
            java = ImageIO.read(new File("java.png"));
            pane = ImageIO.read(new File("pane.png"));

        } catch (IOException ex) {

            Logger.getLogger(DrawingPanel.class.getName()).log(
                    Level.SEVERE, null, ex);
        }
    }

    private void doDrawing(Graphics g) {

        Graphics2D g2d = (Graphics2D) g.create();

        slatetp = new TexturePaint(slate, new Rectangle(0, 0, 90, 60));
        javatp = new TexturePaint(java, new Rectangle(0, 0, 90, 60));
        panetp = new TexturePaint(pane, new Rectangle(0, 0, 90, 60));

        g2d.setPaint(slatetp);
        g2d.fillRect(10, 15, 90, 60);

        g2d.setPaint(javatp);
        g2d.fillRect(130, 15, 90, 60);

        g2d.setPaint(panetp);
        g2d.fillRect(250, 15, 90, 60);

        g2d.dispose();
    }

    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);
        doDrawing(g);
    }
}

public class TexturesEx extends JFrame {

    public TexturesEx() {

        initUI();
    }

    private void initUI() {

        add(new DrawingPanel());

        setTitle("Textures");
        setSize(360, 120);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            TexturesEx ex = new TexturesEx();
            ex.setVisible(true);
        });
    }
}

In the code example, we fill three rectangles with three different textures.

private BufferedImage slate;
private BufferedImage java;
private BufferedImage pane;

BufferedImage is a rectangle of pixels stored in memory. It is one of the most important image types in Swing. Many Swing methods return a BufferedImage to work with.

slate = ImageIO.read(new File("slate.png"));

Here we read the image into the buffered image using ImageIO.read() method. It takes a File object and returns a BufferedImage.

slatetp = new TexturePaint(slate, new Rectangle(0, 0, 90, 60));

We create a TexturePaint class out of the buffered image.

g2d.setPaint(slatetp);
g2d.fillRect(10, 15, 90, 60);

We fill a rectangle with the texture.

Textures
Figure: Textures

Gradients

In computer graphics, gradient is a smooth blending of shades from light to dark or from one colour to another. In 2D drawing programs and paint programs, gradients are used to create colourful backgrounds and special effects as well as to simulate lights and shadows.

GradientsEx.java
package com.zetcode;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawPanel extends JPanel {

    private void doDrawing(Graphics g) {

        Graphics2D g2d = (Graphics2D) g;

        GradientPaint gp1 = new GradientPaint(5, 5,
                Color.red, 20, 20, Color.black, true);

        g2d.setPaint(gp1);
        g2d.fillRect(20, 20, 300, 40);

        GradientPaint gp2 = new GradientPaint(5, 25,
                Color.yellow, 20, 2, Color.black, true);

        g2d.setPaint(gp2);
        g2d.fillRect(20, 80, 300, 40);

        GradientPaint gp3 = new GradientPaint(5, 25,
                Color.green, 2, 2, Color.black, true);

        g2d.setPaint(gp3);
        g2d.fillRect(20, 140, 300, 40);

        GradientPaint gp4 = new GradientPaint(25, 25,
                Color.blue, 15, 25, Color.black, true);

        g2d.setPaint(gp4);
        g2d.fillRect(20, 200, 300, 40);

        GradientPaint gp5 = new GradientPaint(0, 0,
                Color.orange, 0, 20, Color.black, true);

        g2d.setPaint(gp5);
        g2d.fillRect(20, 260, 300, 40);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        doDrawing(g);
    }
}

public class GradientsEx extends JFrame {

    public GradientsEx() {

        initUI();
    }

    private void initUI() {

        DrawPanel dpnl = new DrawPanel();
        add(dpnl);

        setSize(350, 350);
        setTitle("Gradients");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            GradientsEx ex = new GradientsEx();
            ex.setVisible(true);
        });
    }
}

Our code example presents five rectangles with gradients.

GradientPaint gp4 = new GradientPaint(25, 25, 
    Color.blue, 15, 25, Color.black, true);

To work with gradients, we use Java Swing's GradientPaint class. By manipulating the colour values and the starting end ending points, we can get different types of gradients.

g2d.setPaint(gp5);

The gradient is activated calling the setPaint() method.

Gradients
Figure: Gradients

Drawing text

Drawing is done with the drawString() method. We specify the string we want to draw and the position of the text on the window area.

DrawingTextEx.java
package com.zetcode;

import java.awt.EventQueue;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawPanel extends JPanel {

    private void doDrawing(Graphics g) {
        
        Graphics2D g2d = (Graphics2D) g;

        RenderingHints rh = new RenderingHints(
                RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);

        rh.put(RenderingHints.KEY_RENDERING,
                RenderingHints.VALUE_RENDER_QUALITY);

        g2d.setRenderingHints(rh);

        Font font = new Font("URW Chancery L", Font.BOLD, 21);
        g2d.setFont(font);

        g2d.drawString("Not marble, nor the gilded monuments", 20, 30);
        g2d.drawString("Of princes, shall outlive this powerful rhyme;", 20, 60);
        g2d.drawString("But you shall shine more bright in these contents",
                20, 90);
        g2d.drawString("Than unswept stone, besmear'd with sluttish time.",
                20, 120);
        g2d.drawString("When wasteful war shall statues overturn,", 20, 150);
        g2d.drawString("And broils root out the work of masonry,", 20, 180);
        g2d.drawString("Nor Mars his sword, nor war's quick "
                + "fire shall burn", 20, 210);
        g2d.drawString("The living record of your memory.", 20, 240);
        g2d.drawString("'Gainst death, and all oblivious enmity", 20, 270);
        g2d.drawString("Shall you pace forth; your praise shall still "
                + "find room", 20, 300);
        g2d.drawString("Even in the eyes of all posterity", 20, 330);
        g2d.drawString("That wear this world out to the ending doom.", 20, 360);
        g2d.drawString("So, till the judgment that yourself arise,", 20, 390);
        g2d.drawString("You live in this, and dwell in lovers' eyes.", 20, 420);
    }
    
    @Override
    public void paintComponent(Graphics g) {
        
        super.paintComponent(g);
        doDrawing(g);
    }
}

public class DrawingTextEx extends JFrame {

    public DrawingTextEx() {
        
        initUI();
    }

    private void initUI() {

        DrawPanel dpnl = new DrawPanel();
        add(dpnl);

        setSize(500, 470);
        setTitle("Sonnet55");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            DrawingTextEx ex = new DrawingTextEx();
            ex.setVisible(true);
        });
    }
}

In our example, we draw a sonnet on the panel component.

RenderingHints rh = new RenderingHints(
    RenderingHints.KEY_ANTIALIASING,
    RenderingHints.VALUE_ANTIALIAS_ON);

rh.put(RenderingHints.KEY_RENDERING, 
    RenderingHints.VALUE_RENDER_QUALITY);

g2d.setRenderingHints(rh);

This code is to make our text look better. We apply a technique called antialiasing using RenderingHints.

Font font = new Font("URW Chancery L", Font.BOLD, 21);
g2d.setFont(font);

We choose a specific font for our text.

g2d.drawString("Not marble, nor the gilded monuments", 20, 30);

This is the code that draws the text.

Drawing an image

On of the most important capabililies of a toolkit is the ability to display images. An image is an array of pixels. Each pixel represents a colour at a given position. We can use components like JLabel to display an image, or we can draw it using the Java 2D API.

DrawImageEx.java
package com.zetcode;

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawPanel extends JPanel {

    private Image img;

    public DrawPanel() {

        initPanel();
    }

    private void initPanel() {

        loadImage();
        Dimension dm = new Dimension(img.getWidth(null), img.getHeight(null));
        setPreferredSize(dm);
    }

    private void loadImage() {

        img = new ImageIcon("icesid.jpg").getImage();
    }

    private void doDrawing(Graphics g) {

        Graphics2D g2d = (Graphics2D) g;

        g2d.drawImage(img, 0, 0, null);
    }

    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);
        doDrawing(g);
    }
}

public class DrawImageEx extends JFrame {

    public DrawImageEx() {

        initUI();
    }

    private void initUI() {

        DrawPanel dpnl = new DrawPanel();
        add(dpnl);

        setTitle("Image");
        pack();
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            DrawImageEx ex = new DrawImageEx();
            ex.setVisible(true);
        });
    }
}

This example will draw an image on the panel. The image will fit the JFrame window.

private void initPanel() {

    loadImage();
    Dimension dm = new Dimension(img.getWidth(null), img.getHeight(null));
    setPreferredSize(dm);
}

In the initPanel() method we call the loadImage() method. We determine the image dimensions and set the preffered size of the panel component. This will together with the pack() method display the image that will exactly fit the window.

private void loadImage() {

    img = new ImageIcon("icesid.jpg").getImage();
}

The method loads an image from the disk. We use the ImageIcon class. This class simplifies the work with the images in Java Swing.

g2d.drawImage(this.img, 0, 0, null);

The image is drawn using the drawImage() method.

In this chapter, we did some painting in Java Swing. Visit the ZetCode's Java 2D tutorial for additional information about painting in Swing.