/*
 * SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008)
 * Copyright (C) 1991-2000 Silicon Graphics, Inc. All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice including the dates of first publication and
 * either this permission notice or a reference to
 * http://oss.sgi.com/projects/FreeB/
 * shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * SILICON GRAPHICS, INC. BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
 * OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * Except as contained in this notice, the name of Silicon Graphics, Inc.
 * shall not be used in advertising or otherwise to promote the sale, use or
 * other dealings in this Software without prior written authorization from
 * Silicon Graphics, Inc.
 */
/*
** Author: Eric Veach, July 1994.
**
*/

#include <assert.h>
#include "mesh.h"
#include "geom.h"

int __gl_vertLeq(GLUvertex* u, GLUvertex* v)
{
   /* Returns TRUE if u is lexicographically <= v. */

   return VertLeq(u, v);
}

GLfloat __gl_edgeEval(GLUvertex* u, GLUvertex* v, GLUvertex* w)
{
   /* Given three vertices u,v,w such that VertLeq(u,v) && VertLeq(v,w),
    * evaluates the t-coord of the edge uw at the s-coord of the vertex v.
    * Returns v->t - (uw)(v->s), ie. the signed distance from uw to v.
    * If uw is vertical (and thus passes thru v), the result is zero.
    *
    * The calculation is extremely accurate and stable, even when v
    * is very close to u or w.  In particular if we set v->t = 0 and
    * let r be the negated result (this evaluates (uw)(v->s)), then
    * r is guaranteed to satisfy MIN(u->t,w->t) <= r <= MAX(u->t,w->t).
    */
   GLfloat gapL, gapR;

   assert(VertLeq(u, v) && VertLeq(v, w));

   gapL=v->s-u->s;
   gapR=w->s-v->s;

   if (gapL+gapR>0)
   {
      if (gapL<gapR)
      {
         return (v->t-u->t)+(u->t-w->t)*(gapL/(gapL+gapR));
      }
      else
      {
         return (v->t-w->t)+(w->t-u->t)*(gapR/(gapL+gapR));
      }
   }

   /* vertical line */
   return 0;
}

GLfloat __gl_edgeSign(GLUvertex* u, GLUvertex* v, GLUvertex* w)
{
   /* Returns a number whose sign matches EdgeEval(u,v,w) but which
    * is cheaper to evaluate.  Returns > 0, == 0 , or < 0
    * as v is above, on, or below the edge uw.
    */
   GLfloat gapL, gapR;

   assert(VertLeq(u, v) && VertLeq(v, w));

   gapL=v->s-u->s;
   gapR=w->s-v->s;

   if (gapL+gapR>0)
   {
      return (v->t - w->t) * gapL + (v->t - u->t) * gapR;
   }

   /* vertical line */
   return 0;
}

/***********************************************************************
 * Define versions of EdgeSign, EdgeEval with s and t transposed.
 */

GLfloat __gl_transEval(GLUvertex* u, GLUvertex* v, GLUvertex* w)
{
   /* Given three vertices u,v,w such that TransLeq(u,v) && TransLeq(v,w),
    * evaluates the t-coord of the edge uw at the s-coord of the vertex v.
    * Returns v->s - (uw)(v->t), ie. the signed distance from uw to v.
    * If uw is vertical (and thus passes thru v), the result is zero.
    *
    * The calculation is extremely accurate and stable, even when v
    * is very close to u or w.  In particular if we set v->s = 0 and
    * let r be the negated result (this evaluates (uw)(v->t)), then
    * r is guaranteed to satisfy MIN(u->s,w->s) <= r <= MAX(u->s,w->s).
    */
   GLfloat gapL, gapR;

   assert(TransLeq(u, v) && TransLeq(v, w));

   gapL=v->t-u->t;
   gapR=w->t-v->t;

   if (gapL+gapR>0)
   {
      if (gapL<gapR)
      {
         return (v->s-u->s)+(u->s-w->s)*(gapL/(gapL+gapR));
      }
      else
      {
         return (v->s-w->s)+(w->s-u->s)*(gapR/(gapL+gapR));
      }
   }

   /* vertical line */
   return 0;
}

GLfloat __gl_transSign(GLUvertex* u, GLUvertex* v, GLUvertex* w)
{
   /* Returns a number whose sign matches TransEval(u,v,w) but which
    * is cheaper to evaluate.  Returns > 0, == 0 , or < 0
    * as v is above, on, or below the edge uw.
    */
   GLfloat gapL, gapR;

   assert(TransLeq(u, v) && TransLeq(v, w));

   gapL=v->t-u->t;
   gapR=w->t-v->t;

   if (gapL+gapR>0)
   {
      return (v->s-w->s)*gapL+(v->s-u->s)*gapR;
   }

   /* vertical line */
   return 0;
}


int __gl_vertCCW(GLUvertex* u, GLUvertex* v, GLUvertex* w)
{
  /* For almost-degenerate situations, the results are not reliable.
   * Unless the floating-point arithmetic can be performed without
   * rounding errors, *any* implementation will give incorrect results
   * on some degenerate inputs, so the client must have some way to
   * handle this situation.
   */
   return (u->s*(v->t-w->t)+v->s*(w->t-u->t)+w->s*(u->t-v->t))>=0;
}

/* Given parameters a,x,b,y returns the value (b*x+a*y)/(a+b),
 * or (x+y)/2 if a==b==0.  It requires that a,b >= 0, and enforces
 * this in the rare case that one argument is slightly negative.
 * The implementation is extremely stable numerically.
 * In particular it guarantees that the result r satisfies
 * MIN(x,y) <= r <= MAX(x,y), and the results are very accurate
 * even when a and b differ greatly in magnitude.
 */
#define RealInterpolate(a,x,b,y)               \
  (a=(a<0) ? 0 : a,b=(b<0) ? 0 : b,            \
  ((a<=b) ? ((b==0) ? ((x+y)/2)                \
                    : (x+(y-x)*(a/(a+b))))     \
                    : (y+(x-y)*(b/(a+b)))))

#ifndef FOR_TRITE_TEST_PROGRAM
   #define Interpolate(a, x, b, y) RealInterpolate(a, x, b, y)
#else

/* Claim: the ONLY property the sweep algorithm relies on is that
 * MIN(x,y) <= r <= MAX(x,y).  This is a nasty way to test that.
 */
#include <stdlib.h>
extern int RandomInterpolate;

GLfloat Interpolate(GLfloat a, GLfloat x, GLfloat b, GLfloat y)
{
   printf("*********************%d\n",RandomInterpolate);
   if (RandomInterpolate)
   {
      a=1.2*drand48()-0.1f;
      a=(a<0) ? 0 : ((a>1) ? 1 : a);
      b=1.0f-a;
  }

  return RealInterpolate(a, x, b, y);
}

#endif /* FOR_TRITE_TEST_PROGRAM */

#define Swap(a, b)      if (1) { GLUvertex* t=a; a=b; b=t; } else

void __gl_edgeIntersect(GLUvertex* o1, GLUvertex* d1,
                        GLUvertex* o2, GLUvertex* d2,
                        GLUvertex* v)
/* Given edges (o1,d1) and (o2,d2), compute their point of intersection.
 * The computed point is guaranteed to lie in the intersection of the
 * bounding rectangles defined by each edge.
 */
{
   GLfloat z1, z2;

   /* This is certainly not the most efficient way to find the intersection
    * of two line segments, but it is very numerically stable.
    *
    * Strategy: find the two middle vertices in the VertLeq ordering,
    * and interpolate the intersection s-value from these.  Then repeat
    * using the TransLeq ordering to find the intersection t-value.
    */

   if (!VertLeq(o1, d1))
   {
      Swap(o1, d1 );
   }
   if (!VertLeq(o2, d2))
   {
      Swap(o2, d2);
   }
   if (!VertLeq(o1, o2))
   {
      Swap(o1, o2);
      Swap(d1, d2);
   }

   if (!VertLeq(o2, d1))
   {
      /* Technically, no intersection -- do our best */
      v->s=(o2->s+d1->s)/2;
   }
   else
   {
      if (VertLeq(d1, d2))
      {
         /* Interpolate between o2 and d1 */
         z1=EdgeEval(o1, o2, d1);
         z2=EdgeEval(o2, d1, d2);
         if (z1+z2<0)
         {
            z1=-z1; z2=-z2;
         }
         v->s=Interpolate(z1, o2->s, z2, d1->s);
      }
      else
      {
         /* Interpolate between o2 and d2 */
         z1=EdgeSign(o1, o2, d1);
         z2=-EdgeSign(o1, d2, d1);
         if (z1+z2<0)
         {
            z1=-z1; z2=-z2;
         }
         v->s=Interpolate(z1, o2->s, z2, d2->s);
      }
   }

   /* Now repeat the process for t */
   if (!TransLeq(o1, d1))
   {
      Swap(o1, d1);
   }
   if (!TransLeq(o2, d2))
   {
      Swap(o2, d2);
   }
   if (!TransLeq(o1, o2))
   {
      Swap(o1, o2);
      Swap(d1, d2);
   }

   if (!TransLeq(o2, d1))
   {
      /* Technically, no intersection -- do our best */
      v->t=(o2->t+d1->t)/2;
   }
   else
   {
      if (TransLeq(d1, d2))
      {
         /* Interpolate between o2 and d1 */
         z1=TransEval(o1, o2, d1);
         z2=TransEval(o2, d1, d2);
         if (z1+z2<0)
         {
            z1=-z1; z2=-z2;
         }
         v->t=Interpolate(z1, o2->t, z2, d1->t);
      }
      else
      {
         /* Interpolate between o2 and d2 */
         z1=TransSign(o1, o2, d1);
         z2=-TransSign(o1, d2, d1);
         if (z1+z2<0)
         {
            z1=-z1; z2=-z2;
         }
         v->t=Interpolate(z1, o2->t, z2, d2->t);
      }
   }
}
