Zoomable JScrollPane - setViewPosition无法更新 [英] Zoomable JScrollPane - setViewPosition fails to update

问题描述

我正在尝试在JScrollPane中编码可缩放图像。

I'm trying to code a zoom-able image in a JScrollPane.

当图像完全缩小时，它应该是水平和垂直居中。当两个滚动条都出现时，相对于鼠标坐标应始终进行缩放，即在缩放事件之前和之后，图像的同一点应位于鼠标下方。

When the image is fully zoomed out it should be centered horizontally and vertically. When both scroll bars have appeared the zooming should always happen relative to the mouse coordinate, i.e. the same point of the image should be under the mouse before and after the zoom event.

我几乎实现了我的目标。不幸的是，scrollPane.getViewport（）。setViewPosition（）方法有时无法正确更新视图位置。在大多数情况下，调用该方法两次（黑客！）克服了这个问题，但视图仍然闪烁。

I have almost achieves my goal. Unfortunately the "scrollPane.getViewport().setViewPosition()" method sometimes fails to update the view position correctly. Calling the method twice (hack!) overcomes the issue in most cases, but the view still flickers.

我没有解释为什么会发生这种情况。但我确信这不是数学问题。

I have no explanation as to why this is happening. However I'm confident that it's not a math problem.

以下是MWE。要查看我的问题，您可以执行以下操作：

Below is a MWE. To see what my problem is in particular you can do the following:

• 放大直到您有一些滚动条（200％缩放左右） ）


• 通过单击滚动条滚动到右下角


• 将鼠标放在角落并放大两次。第二次你会看到滚动位置如何向中心跳跃。

如果有人能告诉我真的很感激我在哪里遇到问题。谢谢！

package com.vitco;

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseWheelEvent;
import java.awt.image.BufferedImage;
import java.util.Random;

/**
 * Zoom-able scroll panel test case
 */
public class ZoomScrollPanel {

    // the size of our image
    private final static int IMAGE_SIZE = 600;

    // create an image to display
    private BufferedImage getImage() {
        BufferedImage image = new BufferedImage(IMAGE_SIZE, IMAGE_SIZE, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        // draw the small pixel first
        Random rand = new Random();
        for (int x = 0; x < IMAGE_SIZE; x += 10) {
            for (int y = 0; y < IMAGE_SIZE; y += 10) {
                g.setColor(new Color(rand.nextInt(255),rand.nextInt(255),rand.nextInt(255)));
                g.fillRect(x, y, 10, 10);
            }
        }
        // draw the larger transparent pixel second
        for (int x = 0; x < IMAGE_SIZE; x += 100) {
            for (int y = 0; y < IMAGE_SIZE; y += 100) {
                g.setColor(new Color(rand.nextInt(255),rand.nextInt(255),rand.nextInt(255), 180));
                g.fillRect(x, y, 100, 100);
            }
        }
        return image;
    }

    // the image panel that resizes according to zoom level
    private class ImagePanel extends JPanel {
        private final BufferedImage image = getImage();

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D)g.create();
            g2.scale(scale, scale);
            g2.drawImage(image, 0, 0, null);
            g2.dispose();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension((int)Math.round(IMAGE_SIZE * scale), (int)Math.round(IMAGE_SIZE * scale));
        }
    }

    // the current zoom level (100 means the image is shown in original size)
    private double zoom = 100;
    // the current scale (scale = zoom/100)
    private double scale = 1;

    // the last seen scale
    private double lastScale = 1;

    public void alignViewPort(Point mousePosition) {
        // if the scale didn't change there is nothing we should do
        if (scale != lastScale) {
            // compute the factor by that the image zoom has changed
            double scaleChange = scale / lastScale;

            // compute the scaled mouse position
            Point scaledMousePosition = new Point(
                    (int)Math.round(mousePosition.x * scaleChange),
                    (int)Math.round(mousePosition.y * scaleChange)
            );

            // retrieve the current viewport position
            Point viewportPosition = scrollPane.getViewport().getViewPosition();

            // compute the new viewport position
            Point newViewportPosition = new Point(
                    viewportPosition.x + scaledMousePosition.x - mousePosition.x,
                    viewportPosition.y + scaledMousePosition.y - mousePosition.y
            );

            // update the viewport position
            // IMPORTANT: This call doesn't always update the viewport position. If the call is made twice
            // it works correctly. However the screen still "flickers".
            scrollPane.getViewport().setViewPosition(newViewportPosition);

            // debug
            if (!newViewportPosition.equals(scrollPane.getViewport().getViewPosition())) {
                System.out.println("Error: " + newViewportPosition + " != " + scrollPane.getViewport().getViewPosition());
            }

            // remember the last scale
            lastScale = scale;
        }
    }

    // reference to the scroll pane container
    private final JScrollPane scrollPane;

    // constructor
    public ZoomScrollPanel() {
        // initialize the frame
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setSize(600, 600);

        // initialize the components
        final ImagePanel imagePanel = new ImagePanel();
        final JPanel centerPanel = new JPanel();
        centerPanel.setLayout(new GridBagLayout());
        centerPanel.add(imagePanel);
        scrollPane = new JScrollPane(centerPanel);
        scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        frame.add(scrollPane);

        // add mouse wheel listener
        imagePanel.addMouseWheelListener(new MouseAdapter() {
            @Override
            public void mouseWheelMoved(MouseWheelEvent e) {
                super.mouseWheelMoved(e);
                // check the rotation of the mousewheel
                int rotation = e.getWheelRotation();
                boolean zoomed = false;
                if (rotation > 0) {
                    // only zoom out until no scrollbars are visible
                    if (scrollPane.getHeight() < imagePanel.getPreferredSize().getHeight() ||
                            scrollPane.getWidth() < imagePanel.getPreferredSize().getWidth()) {
                        zoom = zoom / 1.3;
                        zoomed = true;
                    }
                } else {
                    // zoom in until maximum zoom size is reached
                    double newCurrentZoom = zoom * 1.3;
                    if (newCurrentZoom < 1000) { // 1000 ~ 10 times zoom
                        zoom = newCurrentZoom;
                        zoomed = true;
                    }
                }
                // check if a zoom happened
                if (zoomed) {
                    // compute the scale
                    scale = (float) (zoom / 100f);

                    // align our viewport
                    alignViewPort(e.getPoint());

                    // invalidate and repaint to update components
                    imagePanel.revalidate();
                    scrollPane.repaint();
                }
            }
        });

        // display our frame
        frame.setVisible(true);
    }

    // the main method
    public static void main(String[] args) {
        new ZoomScrollPanel();
    }
}

注意：我也在这里查看了这个问题< a href =https://stackoverflow.com/questions/2067511/jscrollpane-setviewposition-after-zoom> JScrollPane setViewPosition在缩放之后但不幸的是问题和解决方案略有不同而且不适用。

Note: I have also looked at the question here JScrollPane setViewPosition After "Zoom" but unfortunately the problem and solution are slightly different and do not apply.

编辑

I通过使用hack解决了这个问题，但是我仍然没有更深入地了解底层问题是什么。发生的事情是，当调用setViewPosition时，某些内部状态更改会触发对setViewPosition的其他调用。这些额外的呼叫偶尔会发生。当我阻止它们时，一切都很完美。

I have solved the issue by using a hack, however I'm still no closer to understanding as to what the underlying problem is. What is happening is that when the setViewPosition is called some internal state changes trigger additional calls to setViewPosition. These additional calls only happen occasionally. When I'm blocking them everything works perfectly.

为了解决这个问题，我简单介绍了一个新的布尔变量blocked = false;并替换了行

To fix the problem I simply introduced a new boolean variable "blocked = false;" and replaced the lines

    scrollPane = new JScrollPane(centerPanel);

和

    scrollPane.getViewport().setViewPosition(newViewportPosition);

with

    scrollPane = new JScrollPane();

    scrollPane.setViewport(new JViewport() {
        private boolean inCall = false;
        @Override
        public void setViewPosition(Point pos) {
            if (!inCall || !blocked) {
                inCall = true;
                super.setViewPosition(pos);
                inCall = false;
            }
        }
    });

    scrollPane.getViewport().add(centerPanel);

和

     blocked = true;
     scrollPane.getViewport().setViewPosition(newViewportPosition);
     blocked = false;

如果有人能理解这一点我真的很感激！

I would still really appreciate if someone could make sense of this!

为什么这个黑客工作？有没有更简洁的方法来实现相同的功能？

Why does this hack work? Is there a cleaner way to achieve the same functionality?

推荐答案

这是完整的，功能齐全的代码。我仍然不明白为什么黑客是必要的，但至少它现在按预期工作：

Here is the completed, fully functional Code. I still don't understand why the hack is necessary, but at least it now works as expected:

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseWheelEvent;
import java.awt.image.BufferedImage;
import java.util.Random;

/**
 * Zoom-able scroll panel
 */
public class ZoomScrollPanel {

    // the size of our image
    private final static int IMAGE_SIZE = 600;

    // create an image to display
    private BufferedImage getImage() {
        BufferedImage image = new BufferedImage(IMAGE_SIZE, IMAGE_SIZE, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        // draw the small pixel first
        Random rand = new Random();
        for (int x = 0; x < IMAGE_SIZE; x += 10) {
            for (int y = 0; y < IMAGE_SIZE; y += 10) {
                g.setColor(new Color(rand.nextInt(255),rand.nextInt(255),rand.nextInt(255)));
                g.fillRect(x, y, 10, 10);
            }
        }
        // draw the larger transparent pixel second
        for (int x = 0; x < IMAGE_SIZE; x += 100) {
            for (int y = 0; y < IMAGE_SIZE; y += 100) {
                g.setColor(new Color(rand.nextInt(255),rand.nextInt(255),rand.nextInt(255), 180));
                g.fillRect(x, y, 100, 100);
            }
        }
        return image;
    }

    // the image panel that resizes according to zoom level
    private class ImagePanel extends JPanel {
        private final BufferedImage image = getImage();

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D)g.create();
            g2.scale(scale, scale);
            g2.drawImage(image, 0, 0, null);
            g2.dispose();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension((int)Math.round(IMAGE_SIZE * scale), (int)Math.round(IMAGE_SIZE * scale));
        }
    }

    // the current zoom level (100 means the image is shown in original size)
    private double zoom = 100;
    // the current scale (scale = zoom/100)
    private double scale = 1;

    // the last seen scale
    private double lastScale = 1;

    // true if currently executing setViewPosition
    private boolean blocked = false;

    public void alignViewPort(Point mousePosition) {
        // if the scale didn't change there is nothing we should do
        if (scale != lastScale) {
            // compute the factor by that the image zoom has changed
            double scaleChange = scale / lastScale;

            // compute the scaled mouse position
            Point scaledMousePosition = new Point(
                    (int)Math.round(mousePosition.x * scaleChange),
                    (int)Math.round(mousePosition.y * scaleChange)
            );

            // retrieve the current viewport position
            Point viewportPosition = scrollPane.getViewport().getViewPosition();

            // compute the new viewport position
            Point newViewportPosition = new Point(
                    viewportPosition.x + scaledMousePosition.x - mousePosition.x,
                    viewportPosition.y + scaledMousePosition.y - mousePosition.y
            );

            // update the viewport position
            blocked = true;
            scrollPane.getViewport().setViewPosition(newViewportPosition);
            blocked = false;

            // remember the last scale
            lastScale = scale;
        }
    }

    // reference to the scroll pane container
    private final JScrollPane scrollPane;

    // constructor
    public ZoomScrollPanel() {
        // initialize the frame
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setSize(600, 600);

        // initialize the components
        final ImagePanel imagePanel = new ImagePanel();
        final JPanel centerPanel = new JPanel();
        centerPanel.setLayout(new GridBagLayout());
        centerPanel.add(imagePanel);
        scrollPane = new JScrollPane();

        scrollPane.setViewport(new JViewport() {
            private boolean inCall = false;
            @Override
            public void setViewPosition(Point pos) {
                if (!inCall || !blocked) {
                    inCall = true;
                    super.setViewPosition(pos);
                    inCall = false;
                }
            }
        });

        scrollPane.getViewport().add(centerPanel);
        scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        frame.add(scrollPane);

        // add mouse wheel listener
        imagePanel.addMouseWheelListener(new MouseAdapter() {
            @Override
            public void mouseWheelMoved(MouseWheelEvent e) {
                super.mouseWheelMoved(e);
                // check the rotation of the mousewheel
                int rotation = e.getWheelRotation();
                boolean zoomed = false;
                if (rotation > 0) {
                    // only zoom out until no scrollbars are visible
                    if (scrollPane.getHeight() < imagePanel.getPreferredSize().getHeight() ||
                            scrollPane.getWidth() < imagePanel.getPreferredSize().getWidth()) {
                        zoom = zoom / 1.3;
                        zoomed = true;
                    }
                } else {
                    // zoom in until maximum zoom size is reached
                    double newCurrentZoom = zoom * 1.3;
                    if (newCurrentZoom < 1000) { // 1000 ~ 10 times zoom
                        zoom = newCurrentZoom;
                        zoomed = true;
                    }
                }
                // check if a zoom happened
                if (zoomed) {
                    // compute the scale
                    scale = (float) (zoom / 100f);

                    // align our viewport
                    alignViewPort(e.getPoint());

                    // invalidate and repaint to update components
                    imagePanel.revalidate();
                    scrollPane.repaint();
                }
            }
        });

        // display our frame
        frame.setVisible(true);
    }

    // the main method
    public static void main(String[] args) {
        new ZoomScrollPanel();
    }
}

这篇关于Zoomable JScrollPane - setViewPosition无法更新的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！