/**************************************************************************
 * 
 * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
 * 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, sub license, 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 and this permission notice (including the
 * next paragraph) 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 NON-INFRINGEMENT.
 * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS 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.
 * 
 **************************************************************************/

/* Authors:  Keith Whitwell <keith@tungstengraphics.com>
 */
#include "imports.h"
#include "macros.h"

#include "g_context.h"
#include "g_prim.h"



struct offset_stage {
   struct prim_stage stage;

   GLuint hw_data_offset;

   GLfloat scale;
   GLfloat units;
};



static INLINE struct offset_stage *offset_stage( struct prim_stage *stage )
{
   return (struct offset_stage *)stage;
}


static void offset_begin( struct prim_stage *stage )
{
   struct offset_stage *offset = offset_stage(stage);

   offset->units = stage->generic->setup.offset_units;
   offset->scale = stage->generic->setup.offset_scale;

   stage->next->begin( stage->next );
}


/* Offset tri.  Some hardware can handle this, but not usually when
 * doing unfilled rendering.
 */
static void do_offset_tri( struct prim_stage *stage,
			   struct prim_header *header )
{
   struct offset_stage *offset = offset_stage(stage);   
   GLfloat inv_det = 1.0 / header->det;

   /* Window coords:
    */
   GLfloat *v0 = (GLfloat *)&(header->v[0]->data[0]);
   GLfloat *v1 = (GLfloat *)&(header->v[1]->data[0]);
   GLfloat *v2 = (GLfloat *)&(header->v[2]->data[0]);
   
   GLfloat ex = v0[0] - v2[2];
   GLfloat fx = v1[0] - v2[2];
   GLfloat ey = v0[1] - v2[2];
   GLfloat fy = v1[1] - v2[2];
   GLfloat ez = v0[2] - v2[2];
   GLfloat fz = v1[2] - v2[2];

   GLfloat a = ey*fz - ez*fy;
   GLfloat b = ez*fx - ex*fz;

   GLfloat ac = a * inv_det;
   GLfloat bc = b * inv_det;
   GLfloat zoffset;

   if ( ac < 0.0f ) ac = -ac;
   if ( bc < 0.0f ) bc = -bc;

   zoffset = offset->units + MAX2( ac, bc ) * offset->scale;

   v0[2] += zoffset;
   v1[2] += zoffset;
   v2[2] += zoffset;

   stage->next->tri( stage->next, header );
}


static void offset_tri( struct prim_stage *stage,
			struct prim_header *header )
{
   struct prim_header tmp;

   tmp.det = header->det;
   tmp.v[0] = dup_vert(stage, header->v[0], 0);
   tmp.v[1] = dup_vert(stage, header->v[1], 1);
   tmp.v[2] = dup_vert(stage, header->v[2], 2);

   do_offset_tri( stage->next, &tmp );
}



static void offset_line( struct prim_stage *stage,
		       struct prim_header *header )
{
   stage->next->line( stage->next, header );
}


static void offset_point( struct prim_stage *stage,
			struct prim_header *header )
{
   stage->next->point( stage->next, header );
}


static void offset_end( struct prim_stage *stage )
{
   stage->next->end( stage->next );
}

struct prim_stage *prim_offset( struct generic_context *generic )
{
   struct offset_stage *offset = CALLOC_STRUCT(offset_stage);

   prim_alloc_tmps( &offset->stage, 3 );

   offset->stage.generic = generic;
   offset->stage.next = NULL;
   offset->stage.begin = offset_begin;
   offset->stage.point = offset_point;
   offset->stage.line = offset_line;
   offset->stage.tri = offset_tri;
   offset->stage.end = offset_end;

   return &offset->stage;
}