如何在Graphics2D中设置所需的坐标

Question

我想设置一个从（-1，-1）到（+1，+1）的数学坐标（其中y不增长），并使其适合窗口不管窗口大小如何。

我正在使用的Java SE 7的匿名JComponent的子类和铸造在paintComponent传入Graphics到Graphics2D，然后在Graphics2D

但Graphics2D绘图设置为计算机坐标与大小的变化空间窗户。如何根据窗口大小重新调整它，并让Y向上？以下程序应在右上象限中显示一个黑色方块。

import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.geom.Rectangle2D; 

import javax.swing.JComponent; 
import javax.swing.JFrame; 

public class G { 
    public static void main (String [] args) { 
    JFrame frame = new JFrame(G.class.getCanonicalName()); 
    frame.setUndecorated(true); 
    JComponent component = new JComponent() { 
     private static final long serialVersionUID = 1L; 
     @Override 
     protected void paintComponent (Graphics g) { 
     super.paintComponent(g); 
     paint2D((Graphics2D)g); 
     } 
     protected void paint2D (Graphics2D g2) { 
     g2.draw(new Rectangle2D.Double(0.1, 0.1, 0.9, 0.9)); 
     } 
    }; 
    frame.add(component); 
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    frame.setSize(400, 400); 
    frame.setVisible(true); 
    } 
} 

Answer 1

设置的坐标系统，您想怎么使用transform()和translate()。所以：

1. 你想要原点在（0，高度）;左下方。
2. 然后你想翻转Y轴。

示例代码：

AffineTransform tform = AffineTransform.getTranslateInstance(0, height); 
tform.scale(1, -1); 
g2.setTransform(tform); 

---

[我的编辑版本]：

public static void main (String [] args) { 
    JFrame frame = new JFrame(G2dTransform_Question.class.getCanonicalName()); 
    JComponent component = new JComponent() { 
     private static final long serialVersionUID = 1L; 
     @Override 
     protected void paintComponent (Graphics g) { 
      super.paintComponent(g); 
      paint2D((Graphics2D)g); 
     } 
     protected void paint2D (Graphics2D g2) { 
      AffineTransform tform = AffineTransform.getTranslateInstance(0, getHeight()); 
      tform.scale(getWidth(), -getHeight()); // NOTE -- to make 1.0 'full width'. 
      g2.setTransform(tform); 

      g2.setColor(Color.BLUE); // NOTE -- so we can *see* something. 
      g2.fill(new Rectangle2D.Double(0.1, 0.1, 0.8, 0.8)); // NOTE -- 'fill' works better than 'draw'. 
     } 
    }; 

    frame.setLayout(new BorderLayout()); // NOTE -- make the component size to frame. 
    frame.add(component, BorderLayout.CENTER); 

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    frame.setSize(400, 400); 
    frame.setVisible(true); 
} 

---

[气垫船的版本]：谢谢哈弗！

import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.geom.AffineTransform; 
import java.awt.geom.Rectangle2D; 

import javax.swing.JComponent; 
import javax.swing.JFrame; 

public class G { 
    public static final int PREF_W = 400; 
    public static final int PREF_H = PREF_W; 

public static void main (String [] args) { 
    JFrame frame = new JFrame(G.class.getCanonicalName()); 
    frame.setUndecorated(true); 
    JComponent component = new JComponent() { 
     private static final long serialVersionUID = 1L; 
     @Override 
     protected void paintComponent (Graphics g) { 
     super.paintComponent(g); 
     AffineTransform tform = AffineTransform.getTranslateInstance(0, getHeight()); 
     tform.scale(1, -1); 
     Graphics2D g2 = (Graphics2D) g.create(); 
     g2.setTransform(tform); 
     paint2D(g2); 
     g2.dispose(); 
     } 
     protected void paint2D (Graphics2D g2) { 
     g2.draw(new Rectangle2D.Double(10, 10, 20, 30)); 
     } 

     @Override 
     public Dimension getPreferredSize() { 
     return new Dimension(PREF_W, PREF_H); 
     } 
    }; 
    frame.add(component); 
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    frame.pack(); 
    frame.setVisible(true); 
    } 
}