java - 使用paintComponent()和高CPU使用率

Question

我正在尝试创建一个有趣的游戏，其中包括一个轮子，一个球。每次用户单击按钮时，球都会滚动并随机落在轮子的一个槽上。一切正常，为了创建轮子，我将图像和球(椭圆形对象)放在单独的 JPanel 上。 。功能行为正如我所期望的那样好。但每次运行程序时，CPU 声音很大，Java 应用程序的使用率常常高达 25%。

这太可怕了。经过一段时间的测试，似乎错误出现在我的 painComponent() 内部。重写方法，因为 Java 不间断地重复调用此方法。更全面的调查表明问题在于方法getScaledInstance用于缩放面板内的图像。在我看来，如果我删除此方法，paintComponent()不会被重复调用。

但是，事情是我不知道如何在没有 getScaledInstance 的情况下缩放图像。请注意，我尝试根据 MadProgrammer Java: maintaining aspect ratio of JPanel background image 的示例制作副本

那么，你对此有何看法？有什么办法可以设置背景图片，保持宽高比而不过度调用paintComponent()方法？请注意，我确实尝试使用 Thread.sleep但效果不太好。

这对我来说是相当困难的。不管怎样，感谢您的阅读!

public class WheelPanel2 extends JPanel {

    private BufferedImage image;
    private int time = 0;
    private Image scaled = null;
    private int scaleWidth = 300;
    private int scaleHeight = 300;

    public WheelPanel2() {
        try {
            image = ImageIO.read(new File("img/Basic_roulette_wheel_1024x1024.png"));
            scaled = image.getScaledInstance(scaleWidth, scaleHeight, Image.SCALE_SMOOTH);

        } catch (IOException e) {
            e.printStackTrace();
        }
        setSize(400, 400);
        setPreferredSize(new Dimension(400, 400));
        setBorder(BorderFactory.createLineBorder(Color.BLACK));


        double scaleFactor = Math.min(1d, getScaleFactorToFit(new Dimension(image.getWidth(), image.getHeight()), getSize()));
        int scaleWidth = (int) Math.round(image.getWidth() * scaleFactor);
        int scaleHeight = (int) Math.round(image.getHeight() * scaleFactor);
        Image scaled = image.getScaledInstance(scaleWidth, scaleHeight, Image.SCALE_SMOOTH);

    }

    /**
     * The Paint Method - Create the image of the Wheel and the Ball
     */
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        double scaleFactor = Math.min(1d, getScaleFactorToFit(new Dimension(image.getWidth(), image.getHeight()), getSize()));

        //TRUE WIDTH AND HEIGHT
        int scaleWidth = (int) Math.round(image.getWidth() * scaleFactor);
        int scaleHeight = (int) Math.round(image.getHeight() * scaleFactor);
        scaled = image.getScaledInstance(scaleWidth, scaleHeight, Image.SCALE_SMOOTH);
        int width = getWidth() - 1;
        int height = getHeight() - 1;
        int x = (width - scaled.getWidth(this)) / 2;
        int y = (height - scaled.getHeight(this)) / 2;

        g.drawImage(scaled, x, y, this);
        System.out.println("PAINT");

    }



    /**
     * These two methods are used to automatically resize the wheelpanel and the ball
     */
    private double getScaleFactorToFit(Dimension original, Dimension toFit) {

        double dScale = 1d;

        if (original != null && toFit != null) {

            double dScaleWidth = getScaleFactor(original.width, toFit.width);
            double dScaleHeight = getScaleFactor(original.height, toFit.height);

            dScale = Math.min(dScaleHeight, dScaleWidth);

        }

        return dScale;
    }

    private double getScaleFactor(int iMasterSize, int iTargetSize) {

        double dScale;
        if (iMasterSize > iTargetSize) {

            dScale = (double) iTargetSize / (double) iMasterSize;

        } else {

            dScale = (double) iTargetSize / (double) iMasterSize;

        }

        return dScale;

    }
    public static void main (String[] args) {
        JFrame frame = new JFrame("HI THERE");
        frame.setSize(1000, 1000);
        frame.setLayout(new BorderLayout());
        frame.add(new WheelPanel2(), BorderLayout.CENTER);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(1);

    }
}

如果你尝试运行该程序，你会知道paintComponent被不停地调用。

Answer 1

与其自己缩放图像，不如让 Graphics 来完成，通过调用 drawImage method which takes width and height arguments :

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

    int width = image.getWidth(this);
    int height = image.getHeight(this);
    float scale = Math.min(
        (float) getWidth() / width,
        (float) getHeight() / height);

    width = (int) (width * scale);
    height = (int) (height * scale);

    int x = (getWidth() - width) / 2;
    int y = (getHeight() - height) / 2;

    g.drawImage(image, x, y, width, height, this);
}

在大多数平台上，这将利用系统的图形加速来缩放图像。

如果您想确定使用 SCALE_SMOOTH 的等效项来缩放图像，set the appropriate RenderingHint :

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

    ((Graphics2D) g).setRenderingHint(
        RenderingHints.KEY_INTERPOLATION,
        RenderingHints.VALUE_INTERPOLATION_BICUBIC);

    int width = image.getWidth(this);
    int height = image.getHeight(this);
    float scale = Math.min(
        (float) getWidth() / width,
        (float) getHeight() / height);

    width = (int) (width * scale);
    height = (int) (height * scale);

    int x = (getWidth() - width) / 2;
    int y = (getHeight() - height) / 2;

    g.drawImage(image, x, y, width, height, this);
}