Java - 如何在矩形中直观地居中特定字符串（而不仅仅是字体）

string java swing drawstring

2022-09-03 04:38:02

我试图在JPanel上直观地将用户提供的任意字符串居中。我已经在SO上阅读了数十个其他类似的问题和答案，但没有找到任何直接解决我所遇到的问题的问题和答案。

在下面的代码示例中，getWidth（）和 getHeight（）指的是我放置文本字符串的 JPanel 的宽度和高度。我发现TextLayout.getBounds（）在告诉我包围文本的边界矩形的大小方面做得很好。因此，我认为通过计算文本边界矩形左下角的JPanel上的x和y位置，将文本矩形居中在JPanel矩形中居中会相对简单：

FontRenderContext context = g2d.getFontRenderContext();
messageTextFont = new Font("Arial", Font.BOLD, fontSize);
TextLayout txt = new TextLayout(messageText, messageTextFont, context);
Rectangle2D bounds = txt.getBounds();
xString = (int)((getWidth() - (int)bounds.getWidth()) / 2 );
yString = (int)((getHeight()/2) + (int)(bounds.getHeight()/2));

g2d.setFont(messageTextFont);
g2d.setColor(rxColor);
g2d.drawString(messageText, xString, yString);

这非常适合全部大写的字符串。但是，当我开始使用包含带有降序的小写字母（如g，p，y）的字符串进行测试时，文本不再居中。小写字母（延伸到字体基线以下的部分）的降序在 JPanel 上绘制得太低，无法使文本显示为居中。

就在那时，我发现（感谢SO）传递给drawString（）的y参数指定了绘制文本的基线，而不是下限。因此，再次在SO的帮助下，我意识到我需要通过字符串中降序的长度来调整文本的位置：

....
    TextLayout txt = new TextLayout(messageText, messageTextFont, context);
    Rectangle2D bounds = txt.getBounds();
    int descent = (int)txt.getDescent();
    xString = (int)((getWidth() - (int)bounds.getWidth()) / 2 );
    yString = (int)((getHeight()/2) + (int)(bounds.getHeight()/2) - descent);
....

我用小写字母（如g，p和y）的字符串进行了测试，效果很好！呜呼！但。。。。等。呸。现在，当我尝试仅使用大写字母时，文本在JPanel上太高而无法看起来居中。

就在那时，我发现TextLayout.getDescent（）（以及我为其他类找到的所有其他getDescent（）方法）返回FONT的最大下降而不是特定字符串的最大下降。因此，我的大写字符串被提升为考虑该字符串中甚至没有出现的降序。

我该怎么办？如果我不调整 drawString（）的 y 参数来考虑降序，那么带有降序的小写字符串在 JPanel 上在视觉上太低了。如果我确实调整了 drawString（）的 y 参数来考虑降序，那么不包含任何带有降序字符的字符串在 JPanel 上视觉上太高了。我似乎没有任何方法可以确定基线在给定字符串的文本边框中的位置。因此，我无法弄清楚要将什么y传递给drawString（）。

感谢您的任何帮助或建议。

答案 1

当我唠叨的时候，你可以只使用上下文，例如...TextLayoutGraphicsFontMetrics

Text

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.font.FontRenderContext;
import java.awt.font.TextLayout;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class LayoutText {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private String text;

        public TestPane() {
            text = "Along time ago, in a galaxy, far, far away";
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            g2d.setColor(Color.RED);
            g2d.drawLine(getWidth() / 2, 0, getWidth() / 2, getHeight());
            g2d.drawLine(0, getHeight() / 2, getWidth(), getHeight() / 2);

            Font font = new Font("Arial", Font.BOLD, 48);
            g2d.setFont(font);
            FontMetrics fm = g2d.getFontMetrics();
            int x = ((getWidth() - fm.stringWidth(text)) / 2);
            int y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent();

            g2d.setColor(Color.BLACK);
            g2d.drawString(text, x, y);

            g2d.dispose();
        }
    }

}

好吧，经过一些大惊小怪...

基本上，文本呈现发生在基线处，这使得边界的位置通常出现在该点上方，使其看起来像是文本被绘制在位置上方。yy

为了克服这个问题，我们需要将字体的上升减去字体的下降添加到位置...y

例如。。。

FontRenderContext context = g2d.getFontRenderContext();
Font font = new Font("Arial", Font.BOLD, 48);
TextLayout txt = new TextLayout(text, font, context);

Rectangle2D bounds = txt.getBounds();
int x = (int) ((getWidth() - (int) bounds.getWidth()) / 2);
int y = (int) ((getHeight() - (bounds.getHeight() - txt.getDescent())) / 2);
y += txt.getAscent() - txt.getDescent();

...这就是为什么我喜欢手动渲染文本的原因...

可运行的示例...

Layout

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.font.FontRenderContext;
import java.awt.font.TextLayout;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class LayoutText {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private String text;

        public TestPane() {
            text = "Along time ago, in a galaxy, far, far away";
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            g2d.setColor(Color.RED);
            g2d.drawLine(getWidth() / 2, 0, getWidth() / 2, getHeight());
            g2d.drawLine(0, getHeight() / 2, getWidth(), getHeight() / 2);

            FontRenderContext context = g2d.getFontRenderContext();
            Font font = new Font("Arial", Font.BOLD, 48);
            TextLayout txt = new TextLayout(text, font, context);

            Rectangle2D bounds = txt.getBounds();
            int x = (int) ((getWidth() - (int) bounds.getWidth()) / 2);
            int y = (int) ((getHeight() - (bounds.getHeight() - txt.getDescent())) / 2);
            y += txt.getAscent() - txt.getDescent();

            g2d.setFont(font);
            g2d.setColor(Color.BLACK);
            g2d.drawString(text, x, y);

            g2d.setColor(Color.BLUE);
            g2d.translate(x, y);
            g2d.draw(bounds);

            g2d.dispose();
        }
    }

}

有关详细信息，请参阅使用文本 API...

更新

正如已经建议的那样，您可以使用...GlyphVector

每个单词（和）单独计算以证明差异CatDog

CatDog

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.font.FontRenderContext;
import java.awt.font.GlyphVector;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class LayoutText {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private String text;

        public TestPane() {
            text = "A long time ago, in a galaxy, far, far away";
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            g2d.setColor(Color.RED);
            g2d.drawLine(getWidth() / 2, 0, getWidth() / 2, getHeight());
            g2d.drawLine(0, getHeight() / 2, getWidth(), getHeight() / 2);

            Font font = new Font("Arial", Font.BOLD, 48);
            g2d.setFont(font);

            FontRenderContext frc = g2d.getFontRenderContext();
            GlyphVector gv = font.createGlyphVector(frc, "Cat");
            Rectangle2D box = gv.getVisualBounds();

            int x = 0;
            int y = (int)(((getHeight() - box.getHeight()) / 2d) + (-box.getY()));
            g2d.drawString("Cat", x, y);

            x += box.getWidth();

            gv = font.createGlyphVector(frc, "Dog");
            box = gv.getVisualBounds();

            y = (int)(((getHeight() - box.getHeight()) / 2d) + (-box.getY()));
            g2d.drawString("Dog", x, y);

            g2d.dispose();
        }
    }

}

答案 2

我认为这个答案是正确的方法，但是我过去在自定义字体和获取其边界方面遇到了问题。在一个项目中，我不得不实际获取字体的轮廓并使用这些边界。此方法可能占用更多内存，但它似乎是获取字体边界的可靠方法。

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Font font = new Font("Arial", Font.BOLD, 48);
    String text = "Along time ago, in a galaxy, far, far away";

    Shape outline = font.createGlyphVector(g.getFontMetrics().getFontRenderContext(), text).getOutline();
    // the shape returned is located at the left side of the baseline, this means we need to re-align it to the top left corner. We also want to set it the the center of the screen while we are there
    AffineTransform transform = AffineTransform.getTranslateInstance(
                -outline.getBounds().getX() + getWidth()/2 - outline.getBounds().width / 2, 
                -outline.getBounds().getY() + getHeight()/2 - outline.getBounds().height / 2);
    outline = transform.createTransformedShape(outline);
    g2d.fill(outline);
}

就像我之前说的，尝试使用字体指标，但如果所有其他方法都失败了，请尝试此方法。