AffineTransform

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.geom.AffineTransform;
import java.awt.geom.Rectangle2D;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class MainClass {
	public static void main(String[] args) {
		JFrame jf = new JFrame("Demo");
		Container cp = jf.getContentPane();
		MyCanvas tl = new MyCanvas();
		cp.add(tl);
		jf.setSize(300, 300);
		jf.setVisible(true);
		jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
}

class MyCanvas extends JComponent {
	Shape shape;

	public MyCanvas() {
		shape = create();
	}

	protected Shape create() {
		float cm = 30f;
		return new Rectangle2D.Float(2*cm, 2*cm, cm, cm);
	}

	public void paint(Graphics g) {
		Graphics2D g2 = (Graphics2D) g;

		g2.setPaint(Color.black);
		g2.draw(shape);
		
		AffineTransform trans = new AffineTransform();
		
		trans.scale(-1, 1);
		
		trans.translate(-120, 0);
		
		g2.transform(trans);

		g2.setPaint(Color.red);
		g2.draw(shape);
	}
}

 

这种效果就是翻转之后再往后移120，但如果这样又为何会如此：

 

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.geom.AffineTransform;
import java.awt.geom.Rectangle2D;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class MainClass {
	public static void main(String[] args) {
		JFrame jf = new JFrame("Demo");
		Container cp = jf.getContentPane();
		MyCanvas tl = new MyCanvas();
		cp.add(tl);
		jf.setSize(300, 300);
		jf.setVisible(true);
		jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
}

class MyCanvas extends JComponent {
	Shape shape;

	public MyCanvas() {
		shape = create();
	}

	protected Shape create() {
		float cm = 30f;
		return new Rectangle2D.Float(2*cm, 2*cm, cm, cm);
	}

	public void paint(Graphics g) {
		Graphics2D g2 = (Graphics2D) g;

		g2.setPaint(Color.black);
		g2.draw(shape);
		
		AffineTransform trans = new AffineTransform();
		
		trans.scale(-1, 1);
		
		g2.transform(trans);
		
		trans.translate(-30, 0);
		
		g2.transform(trans);

		g2.setPaint(Color.red);
		g2.draw(shape);
	}
}

 

结果与上图一样，怎么会这样呢，按理往后移30应该是看不到，原因是这里多了句

g2.transform(trans);

这句是什么作用呢，看解释：

 

Composes an AffineTransform object with the Transform in this Graphics2D according to the rule last-specified-first-applied. If the current Transform is Cx, the result of composition with Tx is a new Transform Cx'. Cx' becomes the current Transform for this Graphics2D . Transforming a point p by the updated Transform Cx' is equivalent to first transforming p by Tx and then transforming the result by the original Transform Cx. In other words, Cx'(p) = Cx(Tx(p)). A copy of the Tx is made, if necessary, so further modifications to Tx do not affect rendering.

Parameters:

Tx - the AffineTransform object to be composed with the current Transform

 

这里貌似是有问题的，Cx'怎么感觉就没翻转过呢，就感觉scale和transform两句没有发生作用一样，这是怎么回事呢？原因就是负负得正了，翻转两次，效果取消，看下文：

 

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.geom.AffineTransform;
import java.awt.geom.Rectangle2D;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class MainClass {
    public static void main(String[] args) {
        JFrame jf = new JFrame("Demo");
        Container cp = jf.getContentPane();
        MyCanvas tl = new MyCanvas();
        cp.add(tl);
        jf.setSize(300, 300);
        jf.setVisible(true);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

class MyCanvas extends JComponent {
    Shape shape;

    public MyCanvas() {
        shape = create();
    }

    protected Shape create() {
        float cm = 30f;
        return new Rectangle2D.Float(2*cm, 2*cm, cm, cm);
    }

    public void paint(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;
        
        
        g2.translate(90, 0);
        g2.setPaint(Color.black);
        g2.draw(shape);
        g2.drawLine(0, 0, 0, 5);
        g2.drawLine(-30, 0, -30, 5);
        g2.drawLine(-60, 0, -60, 5);
        g2.drawLine(-90, 0, -90, 5);
        g2.drawLine(-120, 0, -120, 5);
        g2.drawLine(30, 0, 30, 5);
        g2.drawLine(60, 0, 60, 5);
        g2.drawLine(90, 0, 90, 5);
        g2.drawLine(120, 0, 120, 5);
        g2.drawLine(150, 0, 150, 5);
        g2.drawLine(180, 0, 180, 5);
        
        AffineTransform trans = new AffineTransform();
        
        trans.scale(-1, 1);
        
        g2.transform(trans);
        g2.transform(trans);

        g2.setPaint(Color.red);
        g2.draw(shape);
    }
}

 

 

这里有完备的教程：

http://www.glyphic.com/transform/applet/1intro.html

 

记住一点，这个对象AffineTransform是面向坐标系操作的，也就是说它的操作对象是坐标系。