DDA.java

// A simple example of the DDA line-drawing algorithm using characters.

import static java.lang.Math.abs;

public class Main {
  static class Frame {
    private int w, h;
    private char[][] frm;
    
    Frame(
      int w,
      int h)
    {
      this.w = w;
      this.h = h;
      frm = new char[h][w];
      
      for (int y = 0; y < h; y++)
        java.util.Arrays.fill(
          frm[y],
          ' ');
    }
    
    public void set(
      char ch,
      int x,
      int y)
    {
      frm[x][y] = ch;
    }
    
    public void print() {
      for (int y = 0; y < h; y++) {
        for (int x = 0; x < w; x++) {
          System.out.print(frm[y][x]);
        }
        System.out.println();
      }
    }
  }
  
  public static void main(String[] args) {
    Frame f;
    f = new Frame(
      25,
      25);
    line(
      f,
      0,
      0,
      20,
      20);
    f.print();
  }
  
  static void line(
    Frame frame,
    int sx,
    int sy,
    int ex,
    int ey)
  {
    int steps,
      x,
      y,
      dx,
      dy,
      xi,
      yi;
    
    dx = ex - sx;
    dy = ey - sy;
    steps = Math.max(
      abs(dx),
      abs(dy));
    xi = (int)(dx / (steps+0.d));
    yi = (int)(dy / (steps+0.d));
    x = y = 0;
    for (int i = 0; i < steps; i++) {
      x += xi;
      y += yi;
      frame.set(
        '*',
        x,
        y);
    }
  }
}

// And here is the output:
// *                                                                                                                      
//  *                                                                                                                     
//   *                                                                                                                    
//    *                                                                                                                   
//     *                                                                                                                  
//      *                                                                                                                 
//       *                                                                                                                
//        *                                                                                                               
//         *                                                                                                              
//          *