java 什么更重 : Canvas or paintComponent()?

Question

有人可以告诉我应该使用什么在 JPanel 上绘制图形:Canvas，还是简单地在 paintComponent() 中绘制所有内容？我每秒大约 30 次绘制数百个小图像，我想知道哪一个是最轻量级的，以及在什么条件下我应该同时使用这两个图像？谢谢。

Answer 1

这个问题相当广泛，而背景却相当薄弱。

考虑看看 Rotating multiple images causing flickering. Java Graphics2D和 Swing animation running extremely slow例如。

第一个使用 paintComponent 以 25fps(或尽可能接近)渲染多达 10, 000 个旋转图像。

第二个实际上可以对多达 4, 500 个基于组件的图像进行动画处理

以这种速度有效绘画的能力只是整体情况的一个考虑因素

已更新

使用 JPanel 和 Canvas 之间的主要区别在于渲染算法的差异。

使用JPanel，您仍然受重绘管理器的支配。这种方法通常被称为“被动渲染”。也就是说，经理负责确定应该绘制什么内容以及何时绘制。当重绘管理器决定需要绘制某些内容时(例如因为某些操作系统事件已请求应更新部分或整个屏幕)，绘制是临时完成的。

从技术上讲，您无法控制此过程，只能简单地发出重新绘制的请求。由于系统介入并强制更新，您偶尔也可能会遇到一些延迟

Canvas 为您提供了 BufferStrategy，它与底层渲染管道的联系更紧密，可能会使其速度更快。

有了这个，您就可以负责安排重画。这通常称为“主动渲染”。

您仍然可以使用这种方法来处理操作系统...

无论哪种方式，除非您的更新/渲染管道得到很好的优化，否则您仍然可能会遇到很多问题，并且实际上可以通过使用 JPanel 而不是 Canvas 获得更好的性能

就个人而言，如果您不确定或者以前没有做过类似的事情，我会从 JPanel 开始。一般来说，处理起来稍微简单一些。

我更改了链接的示例以维护 FPS 计数器...

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class ZombieLand {

    protected static final Random RND = new Random();

    private static BufferedImage zombie;
    private static int fps = 25;

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

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

                try {
                    zombie = ImageIO.read(getClass().getResource("/MiniFig.png"));
                } catch (IOException ex) {
                    ex.printStackTrace();
                }

                final ZombiePane zombiePane = new ZombiePane();

                final JSlider slider = new JSlider(1, 10000);
                slider.setMajorTickSpacing(1000);
                slider.setMinorTickSpacing(100);
                slider.setPaintTicks(true);
                slider.addChangeListener(new ChangeListener() {
                    @Override
                    public void stateChanged(ChangeEvent e) {
                        JSlider slider = (JSlider) e.getSource();
                        zombiePane.setZombies(slider.getValue());
                    }
                });

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(zombiePane);
                frame.add(slider, BorderLayout.SOUTH);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                SwingUtilities.invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        slider.setValue(10000);
                    }
                });
            }
        });
    }

    public static class ZombiePane extends JPanel {

        private List<ZombieSprite> sprites;
        protected static final Object SPRITE_LOCK = new Object();

        private int desiredCount = 1;

        public ZombiePane() {
            sprites = new ArrayList<>(25);
            sprites.add(new ZombieSprite());
            Thread t = new Thread(new GameLoop());
            t.setDaemon(false);
            t.start();
            Font font = getFont();
            setFont(font.deriveFont(Font.BOLD, 48f));
        }

        public void setZombies(int count) {
            desiredCount = count;
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            synchronized (SPRITE_LOCK) {
                for (ZombieSprite sprite : sprites) {
                    sprite.paint(g2d);
                }
            }
            String text = Integer.toString(sprites.size());
            FontMetrics fm = g2d.getFontMetrics();
            g2d.drawString(text, getWidth() - fm.stringWidth(text), getHeight() - fm.getHeight() + fm.getAscent());

            text = Integer.toString(fps);
            g2d.drawString(text, 0, getHeight() - fm.getHeight() + fm.getAscent());
            g2d.dispose();
        }

        protected void cycle() {
            synchronized (SPRITE_LOCK) {
                if (desiredCount != sprites.size()) {
                    int count = 0;
                    int fill = 100;
                    while (sprites.size() > desiredCount && count < fill) {
                        sprites.remove(0);
                        count++;
                    }
                    count = 0;
                    while (sprites.size() < desiredCount && count < fill) {
                        sprites.add(new ZombieSprite());
                        count++;
                    }
                }

                for (ZombieSprite sprite : sprites) {
                    sprite.update(getWidth(), getHeight());
                }
            }
        }

        public static class ZombieSprite {

            private Point motionDelta;
            private double rotationDelta;

            private Point location;
            private double angle;

            public ZombieSprite() {
                motionDelta = new Point();
                motionDelta.x = (int) ((Math.random() * 3) + 1);
                motionDelta.y = (int) ((Math.random() * 3) + 1);
                if (Math.random() > 0.5) {
                    motionDelta.x *= -1;
                }
                if (Math.random() > 0.5) {
                    motionDelta.y *= -1;
                }
                rotationDelta = (int) ((Math.random() * 9) + 1);
                if (Math.random() > 0.5) {
                    rotationDelta *= -1;
                }
            }

            public void paint(Graphics2D g2d) {
                if (location != null) {
                    Graphics2D g = (Graphics2D) g2d.create();
                    AffineTransform at = new AffineTransform();
                    at.translate(location.x, location.y);
                    at.rotate(Math.toRadians(angle), zombie.getWidth() / 2, zombie.getHeight() / 2);
                    g.setTransform(at);
                    g.drawImage(zombie, 0, 0, null);
                    g.dispose();
                }
            }

            public void update(int width, int height) {
                if (location == null) {
                    angle = (Math.random() * 360d);
                    location = new Point();
                    location.x = (int) (Math.random() * (width - zombie.getWidth()));
                    location.y = (int) (Math.random() * (height - zombie.getHeight()));
                } else {
                    angle += rotationDelta;
                    location.x += motionDelta.x;
                    location.y += motionDelta.y;

                    if (location.x < 0) {
                        location.x = 0;
                        motionDelta.x *= -1;
                    } else if (location.x + zombie.getWidth() > width) {
                        location.x = width - zombie.getWidth();
                        motionDelta.x *= -1;
                    }
                    if (location.y < 0) {
                        location.y = 0;
                        motionDelta.y *= -1;
                    } else if (location.y + zombie.getHeight() > height) {
                        location.y = height - zombie.getHeight();
                        motionDelta.y *= -1;
                    }
                }
            }

        }

        public class GameLoop implements Runnable {

            private long last;
            private long start;
            private int wait;

            private boolean keepRunning = true;

            public void run() {

                // Calculate the optimal/maximum delay time
                // This is converted to nanos so it can be 
                // used to calculate the actual delay...
                long millisPerSecond = TimeUnit.MILLISECONDS.convert(1, TimeUnit.SECONDS);
                long optimalDelay = Math.round(millisPerSecond / 25);

                optimalDelay = TimeUnit.MILLISECONDS.toNanos(optimalDelay);

                // Last start of a "second" loop                    
                long loop = System.nanoTime();
                int frameCount = 0;
                // While gaming...
                while (keepRunning) {
                    // Start of this cycle...
                    long now = System.nanoTime();

                    // Update the state and render the 
                    // current frame...
                    cycle();
                    repaint();

                    // How long did that update take??
                    long timeTaken = System.nanoTime();
                    long delta = timeTaken - now;

                    // Subtract the delay from the maximum delay
                    long delay = optimalDelay - delta;
                    if (delay > 0) {
                        try {
                            // Sleep expects milliseconds...
                            delay = TimeUnit.NANOSECONDS.toMillis(delay);
                            Thread.sleep(delay);
                        } catch (InterruptedException ex) {
                            ex.printStackTrace();
                        }
                    }

                    // Calculate if we've being running for a second yet...
                    long loopDelay = TimeUnit.NANOSECONDS.toSeconds(System.nanoTime() - loop);
                    // If the loop has been cycling for a second...
                    if (loopDelay >= 1) {
                        // Reset the loop time
                        loop = System.nanoTime();
                        System.out.println("FPS = " + frameCount);
                        fps = frameCount;
                        frameCount = 0;
                    } else {
                        // Add another frame to the pile...
                        frameCount++;
                    }
                }
            }
        }
    }
}