import java.awt.*;
import java.awt.Canvas;
import java.util.*;
import java.awt.image.*;

public class nCanvas extends Canvas {
    Image buffImage;
    Graphics gBuff;
	boolean pixels[][];
    
	double rx0=0.0, ry0=0.0, rx1=1.0, ry1=1.0; 
		// real coord of left-bottom point and right-top point
	double rwidth=1.0, rheight=1.0;
        // width and hwight in real
		
    public void makeBuffer(){
        Dimension ps=getSize();
        
        buffImage=createImage(ps.width,ps.height);

        if(buffImage==null){ System.out.println("Could not make buffer.");}
        
        gBuff=buffImage.getGraphics();
        gBuff.setColor(Color.black);
        pixels= new boolean[ps.width][ps.height];
    }

	public void paint(Graphics g){        
        g.drawImage(buffImage,0,0,this);
	}
	
	public void update(Graphics g){
        paint(g);
	}
	
	public void screen(double x0, double y0, double x1, double y1){
		rx0=Math.min(x0,x1); rx1=Math.max(x0,x1);
        ry0=Math.min(y0,y1); ry1=Math.max(y0,y1);
        rwidth=rx1-rx0; rheight=ry1-ry0;
	}
	
	public void eraseBuff(){
        Dimension ps=getSize();
		Color tmpcol;
		
        // gBuff.clearRect(0,0,ps.width,ps.height);
		tmpcol=gBuff.getColor();
		gBuff.setColor(Color.white);
		gBuff.fillRect(0,0,ps.width,ps.height);
        update(this.getGraphics());
        for(int xi=0; xi<ps.width; xi++){
            for(int yi=0; yi<ps.height; yi++){
                pixels[xi][yi]=true;  //true if the point is white.
            }
        }
		gBuff.setColor(tmpcol);
	}
	
	public void drawPoint(int x, int y){
        if(pixels[x][y]){  //if the point is not drawn yet
            gBuff.drawLine(x,y, x,y);
            repaint(1,x,y,1,1);
            pixels[x][y]=false;
        }
    }
	
	public void drawPoint(Dimension pt){
        drawPoint(pt.width, pt.height);
	}
	
	public void drawPoint(double x, double y){
		int xi, yi;
		Dimension s = getSize();
        
        if((rx0<=x) && (x<rx1) && (ry0<=y) && (y<ry1)){
            xi=(int)(Math.floor(((double)s.width * (x-rx0) / rwidth)));
            yi=s.height-(int)(Math.ceil(((double)s.height * (y-ry0) / rheight)));
            drawPoint(xi,yi);
        } 
    }

}