java - 为什么 java.awt.Graphics.drawLine 异常慢？

标签 java swing graphics2d

我正在尝试实现以下“网格”布局。

CompleteImage

该类正在扩展 java.awt.Canvas，并在 paint 函数中绘制这些形状(或线条)。为什么 Canvas ？检查here , 最初尝试做类似的事情。

更新 MCVE 获取上述“布局”的代码:

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

@SuppressWarnings("serial")
public class SO_MCVE extends JPanel {

    private DrawingCanvas _drawingCanvas = null;

    private JButton repaintBtn;

    public SO_MCVE() {
        super(new BorderLayout());

        _drawingCanvas = new DrawingCanvas();
        _drawingCanvas.setSize(new Dimension(600, 600));

        JLabel repaintLabel = new JLabel(
                "<html><div style=\"text-align: center;\">" +
                "REPAINT</html>");
        repaintLabel.setHorizontalAlignment(
                SwingConstants.CENTER);

        repaintBtn = new JButton();
        repaintBtn.add(repaintLabel);
        repaintBtn.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {

                _drawingCanvas.triggerRepaint();
            }
        });

        add(_drawingCanvas, BorderLayout.CENTER);
        add(repaintBtn, BorderLayout.PAGE_END);
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("StackOverflow MCVE for drawLine");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new SO_MCVE());
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                UIManager.put("swing.boldMetal", Boolean.FALSE);
                createAndShowGUI();
            }
        });
    }
}

@SuppressWarnings("serial")
class DrawingCanvas extends Canvas {

    public static final Color lightGreen = new Color(0, 255, 0, 180);
    public static final BasicStroke STROKE1PX = new BasicStroke(1.0f);
    public static final BasicStroke STROKE3PX = new BasicStroke(3.0f);

    private static final int LEFT = 50;
    private static final int RIGHT = 550;
    private static final int TOP = 50;
    private static final int BOTTOM = 550;

    private static final double WIDTH = 500.00d;
    private static final double HEIGHT = 500.00d;

    public DrawingCanvas() {

        setBackground(Color.BLACK);
    }

    public void paint(Graphics g) {
        update(g);
    }

    public void triggerRepaint() {
        repaint();
    }

    public void update(Graphics g) {

        Graphics2D g2 = (Graphics2D) g;
        Dimension dim = getSize();
        int w = (int) dim.getWidth();
        int h = (int) dim.getHeight();

        // Clears the rectangle that was previously drawn
        g2.setPaint(Color.BLACK);
        g2.fillRect(0, 0, w, h);

        drawLines(g2, w, h);
    }

    /** Draw the lines marking the x-y limits **/
    private void drawLines(Graphics2D g2, int w, int h) {

        long start = System.nanoTime();
        System.out.println("Start of drawLines(): " + start);

        // Thick lines
        g2.setPaint(Color.GREEN);
        g2.setStroke(STROKE3PX);
        g2.drawLine(LEFT, 0, LEFT, h);
        g2.drawLine(RIGHT, 0, RIGHT, h);
        g2.drawLine(0, TOP, w, TOP);
        g2.drawLine(0, BOTTOM, w, BOTTOM);

        System.out.println("Done drawing thick lines!");
        long end = System.nanoTime();
        System.out.println("Time taken (ns): " +
                (end - start) + ", Time taken(ms): " +
                ((end - start)/1000/1000));
        start = end;

        // Thin vertical lines
        g2.setPaint(lightGreen);
        g2.setStroke(STROKE1PX);
        int wInc = ((int) WIDTH) / 50;
        for(int i = LEFT; i <= RIGHT; i += wInc) {
            g2.drawLine(i, TOP, i, BOTTOM);
        }

        System.out.println("Done drawing vertical lines!");
        end = System.nanoTime();
        System.out.println("Time taken (ns): " +
                (end - start) + ", Time taken(ms): " +
                ((end - start)/1000/1000));
        start = end;

        // Thin horizontal lines
        g2.setPaint(lightGreen);
        g2.setStroke(STROKE1PX);
        int hInc = ((int) HEIGHT) / 50;
        for(int i = TOP; i <= BOTTOM; i += hInc) {
            g2.drawLine(LEFT, i, RIGHT, i);
        }

        System.out.println("Done drawing horizontal lines!");
        end = System.nanoTime();
        System.out.println("Time taken (ns): " +
                (end - start) + ", Time taken(ms): " +
                ((end - start)/1000/1000));

        System.out.println();
    }
}

上面显示的代码的问题是，每当我调用 repaint() 时，渲染这些行都需要一段时间(大约 3 秒)。
按“重绘”按钮触发 MCVE 中的重绘。
线条会慢慢地一条一条地画出来，如下图所示:

Halfway

那么问题是:
drawLine 这么慢有什么原因吗？我尝试在类似的 for 循环中使用 g2.draw(some Ellipse2D.Double..) 绘制尽可能多(如果不是更多)的椭圆，但没有问题。

注意:使用jre1.7.0_25、Windows 7、Eclipse
使用 System.nanoTime() 的简单基准测试:

Done drawing thick lines!
Time taken (ns): 8858966, Time taken(ms): 8
Done drawing vertical lines!
Time taken (ns): 3649188968, Time taken(ms): 3649
Done drawing horizontal lines!
Time taken (ns): 106730282, Time taken(ms): 106

注意:画“细垂直线”要花很长时间!

更新:
注意:使用jre1.8.0_11、Windows 7、Eclipse
使用 System.nanoTime() 的简单基准测试:

Done drawing thick lines!
Time taken (ns): 110027, Time taken(ms): 0
Done drawing vertical lines!
Time taken (ns): 185567, Time taken(ms): 0
Done drawing horizontal lines!
Time taken (ns): 195419, Time taken(ms): 0

注意:使用jre1.8.0_45、Windows 7、Eclipse
使用 System.nanoTime() 的简单基准测试:

Done drawing thick lines!
Time taken (ns): 6716121, Time taken(ms): 6
Done drawing vertical lines!
Time taken (ns): 2427676380, Time taken(ms): 2427
Done drawing horizontal lines!
Time taken (ns): 83030042, Time taken(ms): 83

Apparently, jre1.8.0_11 works really well?

我如何运行不同的 jre 版本(不确定我做的是否正确!):

VersionSwitch

谢谢! :)

最佳答案

按照 Michael Dibbets 的建议进行操作并使用缓冲。

我用绘制到屏幕外缓冲区然后绘制缓冲区的方法替换了 SO_MCVE.update(Graphics g) 方法:

public void update(Graphics g) {

    Graphics2D g2 = (Graphics2D) g;
    Dimension dim = getSize();
    int w = (int) dim.getWidth();
    int h = (int) dim.getHeight();

    // Create the buffer
    BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
    Graphics2D ig2 = image.createGraphics();

    // Paint everythign on the buffer
    // Clears the rectangle that was previously drawn
    ig2.setPaint(Color.BLACK);
    ig2.fillRect(0, 0, w, h);

    drawLines(ig2, w, h);

    // Paint the buffer
    g2.drawImage(image, 0, 0, null);
}

Start of drawLines(): 1832687816359773
Done drawing thick lines!
Time taken (ns): 2212913, Time taken(ms): 2
Done drawing vertical lines!
Time taken (ns): 37676442, Time taken(ms): 37
Done drawing horizontal lines!
Time taken (ns): 6453455, Time taken(ms): 6

如果您想提高效率，可以将缓冲图像存储为属性，并在尺寸发生变化时替换它。

也就是说，非常有趣的是，绘制垂直线比水平线花费的时间更长。在使用调试器和分析器深入了解 SunGraphics2D 的内部结构后，我仍然无法解释它。

关于java - 为什么 java.awt.Graphics.drawLine 异常慢？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30861201/

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