import java.applet.Applet;
import java.awt.event.*;
import java.awt.*;




/*Applet 6 has much the same function as
Applet 5, except that it is done more
systematically. One new feature is that it 
defines an auxilliary class, called 
a ListenTriangle.  A ListenTriangle is a
Polygon, but also has the ability to tell
if a point is inside or outside of it.  In
this way, one can tell if the mouse has been
clicked on the triangle.  I use 3 ListenTriangles
to build up a more complicated region which
functions as one piece.   A second feature of
this applet is that it uses arrays*/


public class test1 extends Applet {
    PictureCanvas P;    //the auxilliary graphics class
    public void init() {
    setBackground(Color.black);
    P=new PictureCanvas();
    P.resize(320,440);
    add(P);
    }
}


class DBCanvas extends Canvas {
    
    public void update(Graphics g) {
        Graphics g2;
        Image offscreen = null;
        offscreen = createImage(size().width, size().height);
        g2 = offscreen.getGraphics();
        paint(g2);
        g.drawImage(offscreen, 0, 0, this);
	g2.dispose();
	offscreen.flush();
    }
}


class PictureCanvas extends DBCanvas implements MouseListener {

    /**fields**/
    ListenTriangle[] P;  //an array whose members are ListenTriangles
                         //This new class is defined below.

    /**methods**/

  PictureCanvas() { 
    addMouseListener(this);
    setBackground(Color.black);
        /**coordinates for 3 triangles**/
    int x[][]={{100,280,50},{100,130,50},{100,130,280}};
    int y[][]={{100,250,300},{350,250,300},{100,250,110}};
        /**define 3 ListenTriangles**/
    P=new ListenTriangle[3];
    for(int i=0;i<=2;++i) P[i]=new ListenTriangle(x[i],y[i],Color.red);

  }



  public void paint(Graphics g) {   
         /**draw ListenTriangles**/
    for(int i=0;i<=2;++i) 	P[i].render(g);
         /**draw the words**/
    g.setFont(new Font("Helvetica",Font.PLAIN,40));
    g.setColor(Color.yellow);
    g.drawString("Rich: Applet 6",35,40);
    g.setFont(new Font("Helvetica",Font.PLAIN,20));
    g.drawString("Click on the shape to",70,390);
    g.drawString("change its color",70,415);
  }


  /**mouse event methods**/
  public void mousePressed(MouseEvent e) {}   //same remarks as for applet 4
  public void mouseReleased(MouseEvent e) {}
  public void mouseEntered(MouseEvent e) {}
  public void mouseExited(MouseEvent e) {}
  public void mouseClicked(MouseEvent e) {
      Point X=new Point();
      e.consume();
      X.x=e.getX();
      X.y=e.getY();
      
      if((P[0].inside(X)==1)||(P[1].inside(X)==1)||(P[2].inside(X)==1)) {
	  Color temp=P[1].C;
	  if(P[1].C==Color.blue) temp=Color.red;
          if(P[1].C==Color.red) temp=Color.yellow;
          if(P[1].C==Color.yellow) temp=Color.blue;
	  for(int i=0;i<=2;++i) P[i].C=temp;
	  repaint(40,60,300,310);
      }
  }
}

 






class ListenTriangle {

    /**fields**/
    int[] x,y;
    Color C;


    /**methods**/

    /**initialization method**/
    ListenTriangle(int[] x,int[] y,Color C) {
	this.x=x;
	this.y=y;
        this.C=C;
    }
    

    /**some algebra which tells if a point is inside the triangle**/
    int inside(Point p) {     
	double x1,y1,x2,y2;   
	double A1,A2,A3;
	int val;
	x1=p.x-this.x[0];
	y1=p.y-this.y[0];
	x2=p.x-this.x[1];
	y2=p.y-this.y[1];
	A3=x1*y2-y1*x2;
	x1=p.x-this.x[1];
	y1=p.y-this.y[1];
	x2=p.x-this.x[2];
	y2=p.y-this.y[2];
	A1=x1*y2-y1*x2;
	x1=p.x-this.x[2];
	y1=p.y-this.y[2];
	x2=p.x-this.x[0];
	y2=p.y-this.y[0];
	A2=x1*y2-y1*x2;
	val=0;
	if((A1<0)&&(A2<0)&&(A3<0)) val=1;
	if((A1>0)&&(A2>0)&&(A3>0)) val=1;
	return(val);
    }

    /**graphics method**/
    void render(Graphics g) {
	g.setColor(this.C);
	g.fillPolygon(x,y,3);
    }

}