Java-如何在视觉上将特定字符串（不仅仅是字体）放在矩形中

Question

我试图视觉上居中一个任意的用户提供的字符串在JPanel上。我在SO上读了几十个其他类似的问题和答案，但没有找到任何直接解决我遇到的问题的答案。

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。我找到了那个文本布局。getBounds（）可以很好地告诉我包围文本的边框的大小。因此，我认为通过计算文本边界矩形左下角JPanel上的x和y位置，将文本矩形置于JPanel矩形的中心相对简单：

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);

这对于全是大写的字符串非常有效。然而，当我开始测试包含小写字母的字符串（如g、p、y）时，文本不再居中。小写字母（延伸到字体基线以下的部分）的下划线在JPanel上绘制得太低，无法使文本显示为居中。

这时，我发现（多亏了SO），传递给draString（）的y参数指定了绘制文本的基线，而不是下界。因此，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g、p和y等小写字母的字符串进行了测试，效果非常好！呜呼！但是等待啊。现在，当我尝试仅使用大写字母时，文本在JPanel上的位置太高，无法居中显示。

就在那时我发现了文本布局。getDescent（）（以及我为其他类找到的所有其他getDescent（）方法）返回字体的最大下降，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，以解释该字符串中甚至没有出现的派生词。

我该怎么办？如果我不调整drawString（）的y参数来考虑下行，那么在JPanel上带有下行的小写字符串在视觉上就太低了。如果我调整drawString（）的y参数以考虑下行字符，那么在JPanel上不包含任何带有下行字符的字符串在视觉上会过高。我似乎无法确定基线在给定字符串的文本边框中的位置。因此，我无法准确地确定要传递给drawString（）的y是什么。

谢谢你的帮助和建议。

Answer 1

我认为这个答案是正确的方法，但是我在过去有过自定义字体和获得它们的界限的问题。在一个项目中，我不得不求助于实际获取字体的轮廓并使用这些边界。这种方法可能更消耗内存，但它似乎是获得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);
}

正如我之前所说的，尝试使用字体度量，但如果所有其他方法都失败，请尝试此方法。

Answer 2

当我在使用TextLayout时，您可以使用图形上下文的FontMetrics，例如。。。

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，在对。。。

基本上，文本渲染发生在基线，这使得边界的y位置通常出现在这一点之上，使得文本看起来像是被绘制在y位置之上

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y位置。。。

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工渲染文本。。。

可运行的示例。。。

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();
        }
    }

}

了解更多信息，请参阅使用文本API...

更新

如前所述，您可以使用字形向量。。。

分别计算每个单词（Cat和Dog）以显示差异

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();
        }
    }

}