调整应用程序窗口大小时，如何调整应用程序内的图像大小？

Question

当我最大化我的应用程序时，JPanel 内的图像不会随之调整大小。如何在窗口最大化时调整 JPanel 及其内容？

编辑：我正在使用 BufferedImage

Answer 1

这是一个开放式问题。

您是要缩放以填充还是缩放以适合该区域，或者您不关心纵横比？？

按比例填充和按比例调整的区别

此示例将对帧大小的变化做出反应并实时重新缩放图像。

public class TestScaling {

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

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

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new ScalingPane());
                frame.setSize(200, 200);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public class ScalingPane extends javax.swing.JPanel {

        private BufferedImage image;

        public ScalingPane() {
            try {
                image = ImageIO.read(getClass().getResource("/AtDesk.png"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }    
            setBackground(Color.red);
        }

        public double getScaleFactor(int iMasterSize, int iTargetSize) {    
            double dScale = 1;
            dScale = (double) iTargetSize / (double) iMasterSize;

            return dScale;    
        }

        public 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;
        }

        public double getScaleFactorToFill(Dimension masterSize, Dimension targetSize) {
            double dScaleWidth = getScaleFactor(masterSize.width, targetSize.width);
            double dScaleHeight = getScaleFactor(masterSize.height, targetSize.height);

            double dScale = Math.max(dScaleHeight, dScaleWidth);

            return dScale;
        }

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

            double scaleFactor = Math.min(1d, getScaleFactorToFit(new Dimension(image.getWidth(), image.getHeight()), getSize()));
//            double scaleFactor = Math.min(1d, getScaleFactorToFill(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);

            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);
        }
    }
}

更好的解决方案是使用某种背景线程，它可以对组件大小的变化做出反应，并在后台重新缩放原始图像，从而提供低质量和高质量的缩放。

还应注意Image.getScaledInstance 既不是最快也不是最高质量的缩放算法。请查看The Perils of Image.getScaledInstance 了解更多信息。

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Java: maintaining aspect ratio of JPanel background image

Answer 2

一种粗略的方式..

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.draw(image,0,0,getWidth(),getHeight(),this);
    // ..