java - JLayeredPane，背景图像+ "icon"图层

Question

我需要 2 个相互叠置的独立 JPanel(或任何轻量级组件)，并最终直接或通过 JLayeredPane 之类的方式嵌入到 JPanel 中。因此，没有重型部件或玻璃板。下方的 JPanel(名为BackgroundPanel)绘制背景图像或播放视频，同时保持纵横比并使用 Alpha。上面的面板(称为 CompassPanel)上有图标，允许用户添加图标、删除图标以及移动图标(就像图表库一样，但此功能与本文不直接相关)。由于 JNLP 应用程序和部署环境的带宽限制，我无法添加许多外部依赖项。然而，如果有人知道一个轻量级图表库可以处理 alpha 和纵横比维护的背景图像和视频，我很乐意。否则，我一生都无法弄清楚为什么在调整大小后分配这个空间:

我已阅读 JAVA tutorial在没有布局管理器的情况下(不是我想做的事情，你在哪里，GBL!？)，但是对于这些缩放要求以及在调整大小期间使图标停留在图像的同一部分等。我想不出另一种方法来做到这一点。

这是代码，我使用的是Java 1.7。另外，这是我的第一个 stackoverflow，请不要温柔;-)

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Composite;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import javax.swing.border.BevelBorder;

public class Panel extends JPanel {

    private static final Logger logger = Logger.getLogger(Panel.class.getName());

    public Panel() throws IOException {

        final BufferedImage backgroundImage = ImageIO.read(new URL(
                "http://www.windpoweringamerica.gov/images/windmaps/us_windmap_80meters_820w.jpg"));
        final Dimension backgroundImageSize = new Dimension(backgroundImage.getWidth(), backgroundImage.getHeight());
        logger.log(Level.INFO, "Image dimensions: {0}", backgroundImageSize);
        setToolTipText("This is the panel");

        final JLayeredPane layeredPane = new JLayeredPane();
        layeredPane.setBorder(BorderFactory.createLineBorder(Color.RED, 10));
        layeredPane.setToolTipText("This is the layered pane!");
        layeredPane.getInsets().set(0, 0, 0, 0);

        final BackgroundPanel backgroundImagePanel = new BackgroundPanel(backgroundImage);
        final CompassPanel compassPanel = new CompassPanel();
        backgroundImagePanel.setToolTipText("You'll probably never see me, I'm in the background, forever beneath the compass panel");
        compassPanel.setToolTipText("I'm the compass panel");

        // Per http://docs.oracle.com/javase/tutorial/uiswing/layout/none.html, for every container w/o a layout manager, I must:
        // 1) Set the container's layout manager to null by calling setLayout(null). -- I do this here
        // 2) Call the Component class's setbounds method for each of the container's children. --- I do this when resizing
        // 3) Call the Component class's repaint method. --- I do this when resizing

        setLayout(null);
        add(layeredPane);
        layeredPane.add(backgroundImagePanel, JLayeredPane.DEFAULT_LAYER);
        layeredPane.add(compassPanel, JLayeredPane.PALETTE_LAYER);

        // Whenever this panel gets resized, make sure the layered pane gets resized to preserve the aspect ratio of the background image
        addComponentListener(new ComponentAdapter() {
            @Override
            public void componentResized(ComponentEvent evt) {
                Dimension availableSize = calculateAvailableSize(Panel.this);
                Rectangle contentBounds = calculateBoundsToFitImage(availableSize, backgroundImageSize);
                // Ok, this is a big deal. Now I know how big everything has to be, lets force it all to be the right size & repaint.
                layeredPane.setBounds(contentBounds);
                backgroundImagePanel.setBounds(contentBounds);
                compassPanel.setBounds(contentBounds);

                Panel.this.repaint();
                logger.info(String.format("Panel size: %s. Available size: %s. Content Bounds: %s", getSize(), availableSize, contentBounds));
            }
        });
    }

    /**
     * Paints the constant fitted aspect-ratio background image with an alpha of 0.5
     */
    private static class BackgroundPanel extends JPanel {

        private static final Logger logger = Logger.getLogger(BackgroundPanel.class.getName());
        private final AlphaComposite ac = AlphaComposite.getInstance(AlphaComposite.SRC_ATOP, 0.5f);
        private final BufferedImage backgroundImage;

        BackgroundPanel(BufferedImage backgroundImage) {
            setLayout(null);
            this.backgroundImage = backgroundImage;
        }
        private Dimension lastPaintedDimensions = null;

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            final Dimension size = getSize();
            if (lastPaintedDimensions == null || !size.equals(lastPaintedDimensions)) {
                logger.log(Level.INFO, String.format("Painting background on %d x %d", size.width, size.height));
            }
            final Image paintMe = backgroundImage.getScaledInstance(size.width, size.height, Image.SCALE_SMOOTH);
            final Graphics2D g2 = (Graphics2D) g.create();
            g2.drawImage(paintMe, 0, 0, this);
            g2.setColor(Color.BLUE);
            g2.dispose();
            lastPaintedDimensions = size;
        }
    };

    private static class CompassPanel extends JPanel {

        final List<Compass> compassLabels = new ArrayList<>();

        CompassPanel() {
            setLayout(null);
            setOpaque(false);
            setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
        }
    }

    private static class Compass extends JLabel {

        private static final BufferedImage compassImage;

        static {
            try {
                compassImage = ImageIO.read(new URL("http://cdn1.iconfinder.com/data/icons/gur-project-1/32/1_7.png"));
            } catch (IOException ex) {
                throw new RuntimeException("Failed to read compass image", ex);
            }
        }
        final float xPercent, yPercent;

        public Compass(float xPercent, float yPercent) {
            this.xPercent = xPercent;
            this.yPercent = yPercent;
            setIcon(new ImageIcon(compassImage));
            setBorder(BorderFactory.createBevelBorder(BevelBorder.RAISED));
            setOpaque(true);
            setCursor(Cursor.getDefaultCursor());
        }
    }

    public static void main(String[] args) throws IOException {
        final JFrame frame = new JFrame("Hello Stackoverflowwwwwww! Here is a Dynamic Layered Pane Question.");
        frame.setLayout(null);
        frame.setContentPane(new Panel());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 600);
        frame.setVisible(true);
    }

    private static Dimension calculateAvailableSize(final JComponent component) {

        int availableHeight = component.getSize().height;
        int availableWidth = component.getSize().width;

        final Insets insets = component.getInsets();

        availableHeight -= insets.top;
        availableHeight -= insets.bottom;

        availableWidth -= insets.left;
        availableWidth -= insets.right;

        if (component.getBorder() != null) {
            Insets borderInsets = component.getBorder().getBorderInsets(component);
            if (borderInsets != null) {
                availableHeight -= borderInsets.top;
                availableHeight -= borderInsets.bottom;

                availableWidth -= borderInsets.left;
                availableWidth -= borderInsets.right;
            }
        }

        return new Dimension(availableWidth, availableHeight);
    }

    private static Rectangle calculateBoundsToFitImage(Dimension parentSize, Dimension imageSize) {
        final double scaleFactor;
        final int xOffset, yOffset, scaledHeight, scaledWidth;
        {
            final double xScaleFactor = (double) parentSize.width / imageSize.width;
            final double yScaleFactor = (double) parentSize.height / imageSize.height;
            scaleFactor = xScaleFactor > yScaleFactor ? yScaleFactor : xScaleFactor;
            scaledHeight = (int) Math.round(scaleFactor * imageSize.height);
            scaledWidth = (int) Math.round(scaleFactor * imageSize.width);
        }

        xOffset = (int) ((parentSize.width - scaledWidth) / 2.0);
        yOffset = (int) ((parentSize.height - scaledHeight) / 2.0);
        return new Rectangle(xOffset, yOffset, scaledWidth, scaledHeight);
    }
}

Answer 1

呵呵。我刚刚回答了我自己的问题。调用 #setBounds 是相对于您的父容器的，因此需要正确考虑 x 和 y 偏移量，因此这解决了这个问题:

backgroundImagePanel.setBounds(0, 0, contentBounds.width, contentBounds.height);
compassPanel.setBounds(0, 0, contentBounds.width, contentBounds.height);