/* $Id: clip.c,v 1.11 1997/02/13 21:16:09 brianp Exp $ */

/*
 * Mesa 3-D graphics library
 * Version:  2.2
 * Copyright (C) 1995-1997  Brian Paul
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */


/*
 * $Log: clip.c,v $
 * Revision 1.11  1997/02/13 21:16:09  brianp
 * if too many vertices in polygon return VB_SIZE-1, not VB_SIZE
 *
 * Revision 1.10  1997/02/10 21:16:12  brianp
 * added checks in polygon clippers to prevent array overflows
 *
 * Revision 1.9  1997/02/04 19:39:39  brianp
 * changed size of vlist2[] arrays to VB_SIZE per Randy Frank
 *
 * Revision 1.8  1996/12/02 20:10:07  brianp
 * changed the macros in gl_viewclip_polygon() to be like gl_viewclip_line()
 *
 * Revision 1.7  1996/10/29 02:55:02  brianp
 * fixed duplicate vertex bug in gl_viewclip_polygon()
 *
 * Revision 1.6  1996/10/07 23:48:33  brianp
 * changed temporaries to GLdouble in gl_viewclip_polygon()
 *
 * Revision 1.5  1996/10/03 01:43:45  brianp
 * changed INSIDE() macro in gl_viewclip_polygon() to work like other macros
 *
 * Revision 1.4  1996/10/03 01:36:33  brianp
 * changed COMPUTE_INTERSECTION macros in gl_viewclip_polygon to avoid
 * potential roundoff errors
 *
 * Revision 1.3  1996/09/27 01:24:23  brianp
 * removed unused variables
 *
 * Revision 1.2  1996/09/15 01:48:58  brianp
 * removed #define NULL 0
 *
 * Revision 1.1  1996/09/13 01:38:16  brianp
 * Initial revision
 *
 */


#include <string.h>
#include "clip.h"
#include "context.h"
#include "dlist.h"
#include "macros.h"
#include "matrix.h"
#include "types.h"
#include "vb.h"
#include "xform.h"




/* Linear interpolation between A and B: */
#define LINTERP( T, A, B )   ( (A) + (T) * ( (B) - (A) ) )


#define EYE_SPACE 1
#define CLIP_SPACE 2

static GLuint Space;



/*
 * This function is used to interpolate colors, indexes, and texture
 * coordinates when clipping has to be done.  In general, we compute
 *     aux[dst] = aux[in] + t * (aux[out] - aux[in])
 * where aux is the quantity to be interpolated.
 * Input:  dst - index of array position to store interpolated value
 *         t - a value in [0,1]
 *         in - index of array position corresponding to 'inside' vertex
 *         out - index of array position corresponding to 'outside' vertex
 */
static void interpolate_aux( GLcontext* ctx,
                             GLuint dst, GLfloat t, GLuint in, GLuint out )
{
   struct vertex_buffer* VB = ctx->VB;

   if (ctx->ClipMask & CLIP_FCOLOR_BIT) {
      VB->Fcolor[dst][0] = LINTERP( t, VB->Fcolor[in][0], VB->Fcolor[out][0] );
      VB->Fcolor[dst][1] = LINTERP( t, VB->Fcolor[in][1], VB->Fcolor[out][1] );
      VB->Fcolor[dst][2] = LINTERP( t, VB->Fcolor[in][2], VB->Fcolor[out][2] );
      VB->Fcolor[dst][3] = LINTERP( t, VB->Fcolor[in][3], VB->Fcolor[out][3] );
   }
   else if (ctx->ClipMask & CLIP_FINDEX_BIT) {
      VB->Findex[dst] = (GLuint) (GLint) LINTERP( t, (GLfloat) VB->Findex[in],
                                                 (GLfloat) VB->Findex[out] );
   }

   if (ctx->ClipMask & CLIP_BCOLOR_BIT) {
      VB->Bcolor[dst][0] = LINTERP( t, VB->Bcolor[in][0], VB->Bcolor[out][0] );
      VB->Bcolor[dst][1] = LINTERP( t, VB->Bcolor[in][1], VB->Bcolor[out][1] );
      VB->Bcolor[dst][2] = LINTERP( t, VB->Bcolor[in][2], VB->Bcolor[out][2] );
      VB->Bcolor[dst][3] = LINTERP( t, VB->Bcolor[in][3], VB->Bcolor[out][3] );
   }
   else if (ctx->ClipMask & CLIP_BINDEX_BIT) {
      VB->Bindex[dst] = (GLuint) (GLint) LINTERP( t, (GLfloat) VB->Bindex[in],
                                                 (GLfloat) VB->Bindex[out] );
   }

   if (ctx->ClipMask & CLIP_TEXTURE_BIT) {
      /* TODO: is more sophisticated texture coord interpolation needed?? */
      if (Space==CLIP_SPACE) {
	 /* also interpolate eye Z component */
	 VB->Eye[dst][2] = LINTERP( t, VB->Eye[in][2], VB->Eye[out][2] );
      }
      VB->TexCoord[dst][0] = LINTERP(t,VB->TexCoord[in][0],VB->TexCoord[out][0]);
      VB->TexCoord[dst][1] = LINTERP(t,VB->TexCoord[in][1],VB->TexCoord[out][1]);
      VB->TexCoord[dst][2] = LINTERP(t,VB->TexCoord[in][2],VB->TexCoord[out][2]);
      VB->TexCoord[dst][3] = LINTERP(t,VB->TexCoord[in][3],VB->TexCoord[out][3]);
   }

}