How to Draw Constantly Changing Graphics in Java

Introduction

Creating dynamic graphics that update constantly can be a challenging task in Java. In this article, we will demonstrate how to tackle this using efficient techniques and thread synchronization.

Problem Statement

The initial code provided in the question had several performance issues, resulting in slow graphic updates. The goal is to optimize the code to achieve constant updates with improved speed.

Optimized Code

Here's an optimized version of the code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.geom.Ellipse2D;
import java.awt.image.BufferedImage;

public class ZoomPanel extends JPanel {

    private static final int STEP = 40;
    private int iter = 0;
    private long cumulativeTimeTaken = 0;

    // Model to hold pixel colors
    private final Color[][] model = new Color[8][8];

    // Flag to prevent concurrent painting
    private boolean isDrawing = false;

    public static void main(String[] args) {
        final JFrame frame = new JFrame("Image zoom");

        final ZoomPanel zoomPanel = new ZoomPanel();
        frame.getContentPane().add(zoomPanel);
        final Ticker t = new Ticker(zoomPanel);

        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent we) {
                t.done();
                frame.dispose();
            }
        });
        t.start();

        frame.setLocation(new Point(640, 0));
        frame.pack();
        frame.setVisible(true);
    }

    // Sets the pixel color at the given position
    private void setColorAt(int x, int y, Color pixelColor) {
        model[x][y] = pixelColor;
        repaint(40 + x * STEP, 45 + y * STEP, 40 + (x * STEP) - 3, 45 + (y * STEP) - 3);
    }

    // Gets the pixel color at the given position
    private Color getColorAt(int x, int y) {
        return model[x][y];
    }

    // Draws the graphics
    public void paintComponent(Graphics g) {
        long start = System.currentTimeMillis();

        if (!SwingUtilities.isEventDispatchThread()) {
            throw new RuntimeException("Repaint attempt is not on event dispatch thread");
        }

        // Prevent concurrent painting
        isDrawing = true;

        final Graphics2D g2 = (Graphics2D) g;
        g2.setColor(getBackground());

        try {

            for (int x = 0; x < 8; x++) {
                for (int y = 0; y < 8; y++) {
                    g2.setColor(model[x][y]);
                    Ellipse2D e = new Ellipse2D.Double(40 + x * STEP, 45 + y * STEP, STEP - 3, STEP - 3);
                    g2.fill(e);
                    g2.setColor(Color.GRAY);
                    g2.draw(e);
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
        iter++;

        // Display FPS count
        g2.setColor(Color.black);
        long stop = System.currentTimeMillis();
        cumulativeTimeTaken += stop - start;
        StringBuilder sb = new StringBuilder();
        sb.append(iter)
                .append(" frames in ")
                .append((double) (cumulativeTimeTaken) / 1000)
                .append("s.");

        System.out.println(sb);

        // Allow painting again
        isDrawing = false;
    }

    private static class Ticker extends Thread {

        private final Robot robot;

        public boolean update = true;
        private final ZoomPanel view;

        public Ticker(ZoomPanel zoomPanel) {
            view = zoomPanel;
            try {
                robot = new Robot();
            } catch (AWTException e) {
                throw new RuntimeException(e);
            }
        }

        public void done() {
            update = false;
        }

        public void run() {
            int runCount = 0;
            while (update) {
                runCount++;
                if (runCount % 100 == 0) {
                    System.out.println("Ran ticker " + runCount + " times");
                }
                final Point p = MouseInfo.getPointerInfo().getLocation();

                Rectangle rect = new Rectangle(p.x - 4, p.y - 4, 8, 8);
                final BufferedImage capture = robot.createScreenCapture(rect);

                // Synchronized block to prevent concurrent access to the model
                synchronized (view) {
                    // If the panel is not drawing, update the model and repaint
                    if (!view.isDrawing) {
                        for (int x = 0; x < 8; x++) {
                            for (int y = 0; y < 8; y++) {
                                final Color pixelColor = new Color(capture.getRGB(x, y));

                                if (!pixelColor.equals(view.getColorAt(x, y))) {
                                    final int finalX = x;
                                    final int finalY = y;
                                    SwingUtilities.invokeLater(new Runnable() {
                                        public void run() {
                                            view.setColorAt(finalX, finalY, pixelColor);
                                        }
                                    });
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

Improvements

• Robot Optimization: The getPixelColor method in the original code was inefficient. By using createScreenCapture to fetch all 64 pixels at once, we significantly improve performance.
• Smart Clipping: Only the modified region is repainted, reducing unnecessary updates.
• Improved Threading: The model and view are updated on the Event Dispatch Thread, ensuring proper thread synchronization and avoiding potential concurrency issues.
• FPS Monitoring: An FPS counter prints the number of frames updated within a second.
• Synchronization: A lock prevents concurrent painting, further improving stability.

These optimizations result in a vast improvement in performance, with the screen updates appearing virtually instantaneous. The FPS counter provides a measure of the improved speed.

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