curveapplet.java

绘制两条曲线

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;

import java.awt.event.MouseEvent;
import java.awt.geom.CubicCurve2D;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.awt.geom.QuadCurve2D;

import javax.swing.JApplet;
import javax.swing.JComponent;
import javax.swing.event.MouseInputAdapter;

public class CurveApplet extends JApplet {
	public void init(){
		pane = new CurvePane();
		Container content = getContentPane();
		//Add the pane displaying the curves to the content pane for the applet
		content.add(pane);
		
		MouseHandler handler = new MouseHandler();  //Create the listener
		pane.addMouseListener(handler);             //Monitor mouse button presses
		pane.addMouseMotionListener(handler);       //as well as movement 
	}

//class define a pane on which to draw
class CurvePane extends JComponent {
	public CurvePane(){
		quadCurve = new QuadCurve2D.Double(
				                           startQ.x, startQ.y,
				                           control.x, control.y,
				                           endQ.x, endQ.y);
		
		cubicCurve = new CubicCurve2D.Double(
				                             startC.x, startC.y,
				                             controlStart.x,controlStart.y,
				                             controlEnd.x, controlEnd.y,
				                             endC.x, endC.y);
	}
	public void paint(Graphics g){
		Graphics2D g2D = (Graphics2D)g;
		
		//Update the curves with the current control point positions
		quadCurve.ctrlx = ctrlQuad.getCenter().x;
		quadCurve.ctrly = ctrlQuad.getCenter().y;
		cubicCurve.ctrlx1 = ctrlCubic1.getCenter().x;
		cubicCurve.ctrly1 = ctrlCubic1.getCenter().y;
		cubicCurve.ctrlx2 = ctrlCubic2.getCenter().x;
		cubicCurve.ctrly2 = ctrlCubic2.getCenter().y;
		
		//Draw the curves
		g2D.setPaint(Color.blue);
		g2D.draw(quadCurve);
		g2D.draw(cubicCurve);
		
		//Create and draw the markers showing the control points
		g2D.setPaint(Color.red);
		ctrlQuad.draw(g2D);
		ctrlCubic1.draw(g2D);
		ctrlCubic2.draw(g2D);
		
		//draw tangents from the curve end points to the control marker centers
		Line2D.Double tangent = new Line2D.Double(startQ, ctrlQuad.getCenter());
		g2D.draw(tangent);
		tangent = new Line2D.Double(endQ, ctrlQuad.getCenter());
		g2D.draw(tangent);
		
		tangent = new Line2D.Double(startC, ctrlCubic1.getCenter());
		g2D.draw(tangent);
		tangent = new Line2D.Double(endC, ctrlCubic2.getCenter());
		g2D.draw(tangent);
	}
 }

class Marker {
	public Marker(Point2D.Double control) {
		center = control;
		
		//Create circle around control point
		circle = new Ellipse2D.Double(control.x - radius, control.y - radius, 2.0*radius, 2.0*radius);
	}
	
	public void draw (Graphics2D g2D){
		g2D.draw(circle);
	}
	
	//get center of marker - the control point position
	Point2D.Double getCenter(){
		return center;
	}
	
	public boolean contains(double x, double y){
		return circle.contains(x, y);
	}
	
	public void setLocation(double x, double y){
		center.x = x;           //Update control points coordinates
		center.y = y;
		
		circle.x = x - radius;  //Change circle position correspondingly
		circle.y = y - radius;
	}
	Point2D.Double center;
	Ellipse2D.Double circle;
	static final double radius = 3;
  }

class MouseHandler extends MouseInputAdapter {
	public void mousePressed(MouseEvent e){
		
		//check if the cursor inside any marker
		if(ctrlQuad.contains(e.getX(), e.getY()))
			selected = ctrlQuad;
		else if(ctrlCubic1.contains(e.getX(), e.getY()))
			selected = ctrlCubic1;
		else if( ctrlCubic2.contains(e.getX(), e.getY()))
			selected = ctrlCubic2;
	}
	
	public void mouseReleased(MouseEvent e){
		selected = null;
	}
	
	public void mouseDragged(MouseEvent e){
		if(selected != null){
			//Set the marker to current cursor position
			selected.setLocation(e.getX(), e.getY()); 
			pane.repaint();
		}
	}
	
	Marker selected = null;
	
}


       //Points for quadratic curve
       Point2D.Double startQ = new Point2D.Double(50, 150);
       Point2D.Double endQ = new Point2D.Double(150, 150);
       Point2D.Double control = new Point2D.Double(80, 100);
       
       //Points for cubic curve
       Point2D.Double startC = new Point2D.Double(50, 300);
       Point2D.Double endC = new Point2D.Double(150, 300);
       Point2D.Double controlStart = new Point2D.Double(80, 250);
       Point2D.Double controlEnd = new Point2D.Double(160, 250);
       
       //Markers for control points
       Marker ctrlQuad = new Marker(control);
       Marker ctrlCubic1 = new Marker(controlStart);
       Marker ctrlCubic2 = new Marker(controlEnd);
       
       QuadCurve2D.Double quadCurve;
       CubicCurve2D.Double cubicCurve;
       CurvePane pane = new CurvePane();
}