在调整图像大小和同时调整 jPanel 大小时保持纵横比答案

【问题标题】：Maintain aspect ratio when resizing an image and resizing jPanel at the same time在调整图像大小和同时调整 jPanel 大小时保持纵横比
【发布时间】：2018-04-13 04:34:34
【问题描述】：

我试图通过计算原始图像的宽度百分比和高度百分比来保持纵横比，然后根据百分比设置新高度和新宽度，但我的代码有问题：

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.net.URL;

public class Test extends JFrame {
private JPanel principalPanel;
private BufferedImage image;
public Test() {
    setSize(600,600);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    try {
        URL url = new 
       URL("https://boygeniusreport.files.wordpress.com/2017/04/earth.jpg");
        image = ImageIO.read(url);
    } catch (Exception e) {
        System.out.println("Problem loading image");
        e.printStackTrace();
    }
    principalPanel = new JPanel() {
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            int width = image.getWidth();
            int height = image.getHeight();
            int wPercentage = (width*100)/(width+height);
            int hPercentage = (height*100)/(width+height);
            int w = (width+((getHeight()-height)*wPercentage)/hPercentage);
            int h = (height+((getWidth()-width)*hPercentage)/wPercentage);
            g.drawImage(image,0,0,w,h,this);
        }
    };
    setContentPane(principalPanel);
    setVisible(true);
}
public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new Test();
        }
    });
}
}

【问题讨论】：

“但是我的代码有问题”定义“错误”
width+height??
您需要获取图像高度与宽度的比率，然后保持该比率 - 您没有这样做，因为我没有看到您在上面的代码中计算此比率。 width + height 在这些计算中没有位置。
一些例子here.

标签： java swing

【解决方案1】：

解决办法如下：

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.net.URL;

public class Test extends JFrame {
private JPanel principalPanel;
private BufferedImage image;
public Test() {
    setSize(600,600);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    try {
        URL url = new
                URL("https://boygeniusreport.files.wordpress.com/2017/04/earth.jpg");
        image = ImageIO.read(url);
    } catch (Exception e) {
        System.out.println("Problem loading image");
        e.printStackTrace();
    }
    principalPanel = new JPanel() {
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            int original_width = image.getWidth();
            int original_height = image.getHeight();
            int bound_width = getWidth();
            int bound_height = getHeight();
            int new_width = original_width;
            int new_height = original_height;

            // first check if we need to scale width
            if (original_width > bound_width) {
                //scale width to fit
                new_width = bound_width;
                //scale height to maintain aspect ratio
                new_height = (new_width * original_height) / original_width;
            }

            // then check if we need to scale even with the new height
            if (new_height > bound_height) {
                //scale height to fit instead
                new_height = bound_height;
                //scale width to maintain aspect ratio
                new_width = (new_height * original_width) / original_height;
            }
            g.drawImage(image,0,0,new_width,new_height,this);
        }
    };
    setContentPane(principalPanel);
    setVisible(true);
}
public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new Test();
        }
    });
}
}

【讨论】：