////////////////////////////////////////////////////////////
//
//  FF_CLIP.CPP - Form Factor Polygon Clipper Class
//
//  Version:    1.03A
//
//  History:    94/08/23 - Version 1.00A release.
//              94/12/16 - Version 1.01A release.
//              95/02/05 - Version 1.02A release.
//              95/07/21 - Version 1.02B release.
//              96/02/14 - Version 1.02C release.
//              96/04/01 - Version 1.03A release.
//
//  Compilers:  Microsoft Visual C/C++ Professional V1.5
//              Borland C++ Version 4.5
//
//  Author:     Ian Ashdown, P.Eng.
//              byHeart Software Limited
//              620 Ballantree Road
//              West Vancouver, B.C.
//              Canada V7S 1W3
//              Tel. (604) 922-6148
//              Fax. (604) 987-7621
//
//  Copyright 1994-1996 byHeart Software Limited
//
//  The following source code has been derived from:
//
//    Ashdown, I. 1994. Radiosity: A Programmer's
//    Perspective. New York, NY: John Wiley & Sons.
//
//  It may be freely copied, redistributed, and/or modified
//  for personal use ONLY, as long as the copyright notice
//  is included with all source code files.
//
////////////////////////////////////////////////////////////

#include "ff_clip.h"

// Clip element
int FormClip::Clip( Element3 *pelem, FormPoly &out, WORD
    poly_id )
{
  int i;            // Loop index
  int num_vert;     // Number of vertices
  Vertex3 *pvert;   // 3-D world space vertex pointer
  Vector4 hv;       // 4-D homogeneous co-ord vertex

  out.Reset(poly_id);   // Reset output polygon

  num_vert = pelem->GetNumVert();
  for (i = 0; i < num_vert; i++)
  {
    // Get world space vertex position pointer
    pvert = pelem->GetVertexPtr(i);

    // Set homogeneous co-ordinates vertex
    hv.ProjTransform(pvert->GetPosn(), vtm);

    pclip->Clip(hv, out);       // Clip polygon edge
  }

  pclip->Close(out);    // Close polygon
      
  return out.GetNumVert();
}

// Output view space vertex
void FormClipEdge::Output( Vector4 &v, FormPoly &out )
{
  if (pnext != NULL)    // More planes ?
    pnext->Clip(v, out);
  else
    out.AddVertex(v);
}

// Calculate intersection vertex
Vector4 FormClipEdge::Intersect( Vector4 &s, Vector4 &e )
{
  double d, t;  // Temporary variables
  Vector4 r;    // Temporary vector

  // Calculate parameter
  r = (e - s);
  d = Dot(normal, r);

  if (fabs(d) > MIN_VALUE)
    t = -Dot(normal, s) / d;
  else
    t = 1.0;

  if (t < 0.0)  // Ensure lower limit
    t = 0.0;

  if (t > 1.0)  // Ensure upper limit
    t = 1.0;

  // Calculate intersection vertex co-ordinates
  r *= t;

  return (s + r);
}

// Clip polygon edge
void FormClipEdge::Clip( Vector4 &current, FormPoly &out )
{
  BOOL curr_inside;     // Current point inside flag
  Vector4 isect;        // Intersection vertex

  // Determine vertex visibility
  curr_inside = IsInside(current);

  if (first_flag == FALSE)      // First vertex seen ?
  {
    first = current;
    first_inside = curr_inside;
    first_flag = TRUE;
  }
  else
  {
    // Does edge intersect plane ?
    if (start_inside ^ curr_inside)
    {
      isect = Intersect(start, current);
      Output(isect, out);
    }
  }

  if (curr_inside == TRUE)
    Output(current, out);

  start = current;
  start_inside = curr_inside;
}

// Close polygon
void FormClipEdge::Close( FormPoly &out )
{
  Vector4 isect;        // Intersection vertex

  if (first_flag == TRUE)
  {
    // Does edge intersect plane ?
    if (start_inside ^ first_inside)
    {
      isect = Intersect(start, first);
      Output(isect, out);
    }

    if (pnext != NULL)  // More planes ?
      pnext->Close(out);

    // Reset first vertex seen flag
    first_flag = FALSE;
  }
}