// test_meet.java   compile    javac -cp . test_meet.java
//                  execute    java  -cp . test_meet > test_meet_java.out

public class test_meet  // line p1 to p2, line p3 to p4 
{
  public test_meet()
  {
    double p1x, p1y, p2x, p2y, p3x, p3y, p4x, p4y, pix, piy;
    double xmax, xmin, ymax, ymin, dx, dy, x, y;
    int nx = 9;
    int ny = 9;
    double ddx = 0.01;
    double ddy = 0.01;
    int nline = 3;
    int found = 0;
    double mat[][] = new double[2][3];
    double p[] = new double[2];
    double pmeet[] = new double[2];
    double line[][] = new double[3][4];
    boolean up = false;
    boolean down = false;
    boolean left = false;
    boolean right = false;
    
    System.out.println("test_meet.java running");
    System.out.println("find intersect of line p1 to p2 with line p3 to p4");
    System.out.println("point of intersect pix, piy computed");
    line[0][0] =  4.0; // lp1 triangle 
    line[0][1] =  1.0;
    line[0][2] =  1.0; // lp2
    line[0][3] = 12.0;
    line[1][0] =  1.0; // lp2
    line[1][1] = 12.0;
    line[1][2] = 12.0; // lp3
    line[1][3] =  9.0;
    line[2][0] = 12.0; // lp3
    line[2][1] =  9.0;
    line[2][2] =  4.0; // lp1
    line[2][3] =  1.0;
    xmin =  2.0;
    xmax = 11.0;
    ymin =  2.0;
    ymax = 11.0;
    dx = (xmax-xmin)/(double)nx;
    dy = (ymax-ymin)/(double)ny;
    System.out.println("nx="+nx);
    System.out.println("xmax="+xmax+"  xmin="+xmin+"  dx="+dx);
    System.out.println("ny="+ny);
    System.out.println("ymax="+ymax+"  ymin="+ymin+"  dy="+dy);
    for(int i=0; i<nline; i++)
    {
      System.out.println("line["+i+"i][0]="+line[i][0]+"  line[i][1] ="+line[i][1]);
      System.out.println("line["+i+"i][2]="+line[i][2]+"  line[i][3] ="+line[i][3]);
      System.out.println(" ");
    } // end i

    x = xmin;
    for(int i=0; i<=nx; i++)
    {
      y = ymin;
      for(int j=0; j<=ny; j++)
      {
	up = false;
        down = false;
        left = false;
        right = false;

        System.out.println("point inside? x="+x+"  y="+y);
	found = 0; // need found == 4 for inside
        for(int m=0; m<nline; m++) // check x up hits
	{
	  p1x = line[m][0];
	  p1y = line[m][1];
	  p2x = line[m][2];
	  p2y = line[m][3];
	  p3x = x;
	  p3y = y;
	  p4x = x + ddx; // fails if p3x-p4x==0  checking up
	  p4y = y + ymax; // checking up
          meet(p1x, p1y, p2x, p2y, p3x, p3y, p4x, p4y, pmeet); // pix, piy
          pix = pmeet[0];
	  piy = pmeet[1];
          System.out.println("up    m="+m+" pix,piy="+pmeet[0]+"  "+pmeet[1]);
	  if(((pix>=p1x && pix<=p2x) || (pix<=p1x && pix>=p2x)) & piy>y )
	  {
	    up=true;
	  }

	  p4x = x + ddx;
	  p4y = y - ymax; // checking down
          meet(p1x, p1y, p2x, p2y, p3x, p3y, p4x, p4y, pmeet); // pix, piy
          pix = pmeet[0];
	  piy = pmeet[1];
          System.out.println("down  m="+m+" pix,piy="+pmeet[0]+"  "+pmeet[1]);
	  if(((pix>=p1x && pix<=p2x) || (pix<=p1x && pix>=p2x)) & piy<y )
	  {
	    down=true;
	  }

	  p4x = x - xmax;   // checking left
	  p4y = y + ddy;
          meet(p1x, p1y, p2x, p2y, p3x, p3y, p4x, p4y, pmeet); // pix, piy
          pix = pmeet[0];
	  piy = pmeet[1];
          System.out.println("left  m="+m+" pix,piy="+pmeet[0]+"  "+pmeet[1]);
	  if(((piy>=p1y && piy<=p2y) || (piy<=p1y && piy>=p2y)) & pix<x )
	  {
	    left=true;
	  }

          p4x = x + xmax;   // checking right
	  p4y = y + ddy;
          meet(p1x, p1y, p2x, p2y, p3x, p3y, p4x, p4y, pmeet); // pix, piy
          pix = pmeet[0];
	  piy = pmeet[1];
          System.out.println("right m="+m+" pix,piy="+pmeet[0]+"  "+pmeet[1]);
	  if(((piy>=p1y && piy<=p2y) || (piy<=p1y && piy>=p2y)) & pix>x )
	  {
	    right=true;
	  }
	  
	  if(up && down && left && right)
          {
            System.out.println("point is inside");
            System.out.println(" ");
            break; // exit m loop
	  }
	} // end m
        System.out.println(" ");
	y = y + dy;
      } // end j
      System.out.println(" ");
      x = x + dx;
    } // end y

    System.out.println("test_meet.java finished");
  } // end test_meet

  void meet(double p1x, double p1y, double p2x, double p2y,
	    double p3x, double p3y, double p4x, double p4y,
	    double pmeet[]) // pix, piy
  {
    double d12x, d12y, d34x, d34y, pix, piy;
    double p[] = {0.0, 0.0, 0.0};
    double mat[][] = new double[2][3];
    pmeet[0] = 0.0;
    pmeet[1] = 0.0;
    d12x = p2x-p1x;
    d12y = p2y-p1y;
    d34x = p4x-p3x;
    d34y = p4y-p3y;
    // System.out.println("d12x="+d12x+"  d12y="+d12y);
    // System.out.println("d34x="+d34x+"  d34y="+d34y);
    // line p1 to p2  (x-p1x)/d12x = (y-p1y)/d12y 
    // x/d12x - y/d12y = p1x/d12x - p1y/d12y  
    // line p3 to p4  (x-p3x)/d34x = (y-p3y)/d34y
    // x/d34x - y/d34y = p3x/d34x - p3y/d34y
    // solve two equations in two unknowns
    if(Math.abs(d12x)<1.0e-6 || Math.abs(d12y)<1.0e-6) {return;}
    if(Math.abs(d34x)<1.0e-6 || Math.abs(d34y)<1.0e-6) {return;}
    mat[0][0] = 1.0/d12x;
    mat[0][1] = -1.0/d12y;
    mat[0][2] = p1x/d12x - p1y/d12y;
    mat[1][0] = 1.0/d34x;
    mat[1][1] = -1.0/d34y;
    mat[1][2] = p3x/d34x - p3y/d34y; 
    new simeq(2,mat,p);
    pix = p[0];
    piy = p[1];
    pmeet[0] = pix;
    pmeet[1] = piy;
  } // end meet

  public static void main (String[] args)
  {
    new test_meet();
  }
} // end test_meet