zqb_cliplinebyrect.hpp

/* zqb_cliplinebyrect.hpp */
/* $Id: zqb_cliplinebyrect.hpp,v 1.6 2008/04/24 11:10:07 vlad Exp $ */
#ifndef __zqb_cliplinebyrect_hpp
#define __zqb_cliplinebyrect_hpp

#include "zqb_macros.h"


template<class T> bool
ZqbClipLineByRect (T x[2],
           T y[2],
           T rx[2],
           T ry[2]
           )
{
  /* Resulting coordinates of line segment */
  T xf[2], yf[2];

  /* Sorting order of rectangle corner coordinates */
  ZqbASCENT(rx[0], rx[1]);
  ZqbASCENT(ry[0], ry[1]);

  /* Simply outside the rectangle */
  if((x[0] < rx[0] && x[1] < rx[0]) || (x[0] > rx[1] && x[1] > rx[1]) ||
     (y[0] < ry[0] && y[1] < ry[0]) || (y[0] > ry[1] && y[1] > ry[1]))
    return false;

  /* Simply inside the rectangle */
  if(rx[0] <= x[0] && x[0] <= rx[1] && rx[0] <= x[1] && x[1] <= rx[1] &&
     ry[0] <= y[0] && y[0] <= ry[1] && ry[0] <= y[1] && y[1] <= ry[1])
    return true;

  /* Horizontal or vertical line segment? */
  if(x[0] != x[1] && y[0] == y[1])
    {
      /* Horizontal line */
      if(x[0] > x[1])
    {
      xf[0] = ZqbMIN(rx[1], x[0]);
      xf[1] = ZqbMAX(rx[0], x[1]);
    }
      else
    {
      xf[1] = ZqbMIN(rx[1], x[1]);
      xf[0] = ZqbMAX(rx[0], x[0]);
    }
      yf[0] = yf[1] = y[0];
    }
  else if(x[0] == x[1] && y[0] != y[1])
    {
      /* Vertical line */
      if(y[0] > y[1])
    {
      yf[0] = ZqbMIN(ry[1], y[0]);
      yf[1] = ZqbMAX(ry[0], y[1]);
    }
      else
    {
      yf[1] = ZqbMIN(ry[1], y[1]);
      yf[0] = ZqbMAX(ry[0], y[0]);
    }
      xf[0] = xf[1] = x[0];
    }
  else
    {
      /* Slanting line */

      /* Segment --> line */
      double    k = (y[1] - y[0])/(x[1] - x[0]);
      double    b = y[0] - k * x[0];

      /* min and max x-coord between line intersection with ry[0] and
         ry[1] */
      double    minx = ZqbMIN((ry[0] - b)/k, (ry[1] - b)/k);
      double    maxx = ZqbMAX((ry[0] - b)/k, (ry[1] - b)/k);

      if(rx[1] < minx || rx[0] > maxx)
    /* line don't intersect rectangle area */
    return false;

      /* min and max x-coord taking into account rectangle bounds */
      minx = ZqbMAX(rx[0], minx);
      maxx = ZqbMIN(rx[1], maxx);

      if(x[0] < minx && x[1] < minx ||
     x[0] > maxx && x[1] > maxx)
    /* segment don't intersect rectangle area */
    return false;

      if(x[0] > x[1])
    {
      xf[0] = ZqbMIN(x[0], maxx);
      xf[1] = ZqbMAX(x[1], minx);
    }
      else
    {
      xf[1] = ZqbMIN(x[1], maxx);
      xf[0] = ZqbMAX(x[0], minx);
    }
      yf[0] = k * xf[0] + b;
      yf[1] = k * xf[1] + b;
    }

  /* Results writing */
  x[0] = xf[0];  y[0] = yf[0];
  x[1] = xf[1];  y[1] = yf[1];

  return true;

}


#endif /* zqb_cliplinebyrect.hpp */