clip.c

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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <assert.h>
#include <math.h>
#include <stdlib.h>

#include "global.h"
#include "data.h"
#include "draw.h"
#include "mymem.h"

#ifdef HAVE_LIBDMALLOC
#include <dmalloc.h>
#endif

bool
ClipLine (double minx, double miny, double maxx, double maxy,
          double *x1, double *y1,
          double *x2, double *y2,
          double margin)
{
  double d, r;

  minx -= margin;
  miny -= margin;
  maxx += margin;
  maxy += margin;

  /* clip first point on left side */
  if (*x1 < minx)
    {
      if (*x2 < minx)
        return false;
      d = *x2 - *x1;
      r = (minx - *x1) / d;
      *x1 = minx;
      *y1 += r * (*y2 - *y1);
    }
  /* clip second point on left side */
  if (*x2 < minx)
    {
      d = *x1 - *x2;
      r = (minx - *x2) / d;
      *x2 = minx;
      *y2 += r * (*y1 - *y2);
    }
  /* clip first point on right side */
  if (*x1 > maxx)
    {
      if (*x2 > maxx)
        return false;
      d = *x2 - *x1;
      r = (maxx - *x1) / d;
      *x1 = maxx;
      *y1 += r * (*y2 - *y1);
    }
  /* clip second point on right side */
  if (*x2 > maxx)
    {
      d = *x1 - *x2;
      r = (maxx - *x2) / d;
      *x2 = maxx;
      *y2 += r * (*y1 - *y2);
    }

  /* clip first point on top */
  if (*y1 < miny)
    {
      if (*y2 < miny)
        return false;
      d = *y2 - *y1;
      r = (miny - *y1) / d;
      *y1 = miny;
      *x1 += r * (*x2 - *x1);
    }
  /* clip second point on top */
  if (*y2 < miny)
    {
      d = *y1 - *y2;
      r = (miny - *y2) / d;
      *y2 = miny;
      *x2 += r * (*x1 - *x2);
    }
  /* clip first point on bottom */
  if (*y1 > maxy)
    {
      if (*y2 > maxy)
        return false;
      d = *y2 - *y1;
      r = (maxy - *y1) / d;
      *y1 = maxy;
      *x1 += r * (*x2 - *x1);
    }
  /* clip second point on top */
  if (*y2 > maxy)
    {
      d = *y1 - *y2;
      r = (maxy - *y2) / d;
      *y2 = maxy;
      *x2 += r * (*x1 - *x2);
    }
  return true;
}