CS 100: Lecture L6

February 11

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Filling in a Semicircle: A For-loop graphics example

// L6A A solid semicircle.

import java.io.*;
import java.awt.*;

public class CUCSDrawing extends Frame
{
    final int r  = 250;       // The radius of the semicircle
    final int xc = 400;  
    final int yc = 300;       // The center of the semicircle = (xc,yc).
    
	public void paint(Graphics g)
	{
	   // We'll draw a magenta semicircle with the "dome" on top by drawing every possible
	   // vertical line segment that is inside the semicircle.
	   
       g.setColor(Color.magenta);
	   int x;                        // The horizontal coordinate of the current "fill" line.
	   int y;                        // Vertical coordinare of the "top" of the current fill line.
	   for (x=xc-r;x<=xc+r;x=x+1)
	   {
	      y = (int) (yc -  Math.sqrt(Math.pow(r,2)-Math.pow(x-xc,2)));
	      g.drawLine(x,yc,x,y);
	   }
	}
	
}

public class L6A
{
	public static void main(String args[])
	{
		CUCSDrawing d = new CUCSDrawing();
		d.resize(900,750);                     // Modify as appropriate.
		d.move(0,75);
		d.setTitle("Drawing");                 // Modify as appropriate.
		d.show();
		d.toFront();
	}
}

Drawing a Grid

// L6B: An n-by-n grid with a disk on the center tile assuming n is odd.


import java.io.*;
import java.awt.*;

public class CUCSDrawing extends Frame
{
    
    
    final int left = 100;            // Horizontal coordinate of the board's left edge.
    final int top  = 100;            // Vertical coordinate of the board's top edge.
    final int n = 9;                 // The board size. (The board will be n-by-n).
    final int s = 50;                // Gridlines are spaced this far apart.
    
	public void paint(Graphics g)
	{
	   int k;                           // Gridline ndex
	   int v = top;                     // Vertical coordinate of the kth horizontal gridline.
	   int h = left;                    // Horizontal coordinate of the kth vertical gridline.
	   int right = left+n*s;            // Horizontal coordinate of the board's right edge.      
	   int bottom = top+n*s;            // Vertical coordinate of the board's bottom edge.
	
	   for (k=1;k<=n+1;k=k+1)
	   {
	      // Draw the kth horizontal gridline and the kth vertical gridline.
	      g.drawLine(left,v,right,v);
	      g.drawLine(h,top,h,bottom);
	      h = h+s;
	      v = v+s;   
	   }
	   // Now place the disk on the center tile.
	   // The upper left corner of the center tile is over m*s and down m*s
	   // from the upper left corner of the grid where m = n/2 in
	   // integer arithmetic.
	   
	   int m = n/2;               
	   g.setColor(Color.magenta);
	   g.fillOval(left+m*s,top+m*s,s,s);
	   	
	}
	
}

public class L6B
{
	public static void main(String args[])
	{
		CUCSDrawing d = new CUCSDrawing();
		d.resize(900,750);                    
		d.move(0,75);
		d.setTitle("A Grid");                 
		d.show();
		d.toFront();
	}
}