1/**************************************************************************
2 *
3 * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
4 * All Rights Reserved.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a
7 * copy of this software and associated documentation files (the
8 * "Software"), to deal in the Software without restriction, including
9 * without limitation the rights to use, copy, modify, merge, publish,
10 * distribute, sub license, and/or sell copies of the Software, and to
11 * permit persons to whom the Software is furnished to do so, subject to
12 * the following conditions:
13 *
14 * The above copyright notice and this permission notice (including the
15 * next paragraph) shall be included in all copies or substantial portions
16 * of the Software.
17 *
18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
19 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
20 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
21 * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS BE LIABLE FOR
22 * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
23 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
24 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
25 *
26 **************************************************************************/
27
28/**
29 * \brief  Drawing stage for polygon culling
30 */
31
32/* Authors:  Keith Whitwell <keith@tungstengraphics.com>
33 */
34
35
36#include "util/u_memory.h"
37#include "pipe/p_defines.h"
38#include "draw_pipe.h"
39
40
41struct cull_stage {
42   struct draw_stage stage;
43   unsigned cull_face;  /**< which face(s) to cull (one of PIPE_FACE_x) */
44   unsigned front_ccw;
45};
46
47
48static INLINE struct cull_stage *cull_stage( struct draw_stage *stage )
49{
50   return (struct cull_stage *)stage;
51}
52
53
54static void cull_tri( struct draw_stage *stage,
55		      struct prim_header *header )
56{
57   const unsigned pos = draw_current_shader_position_output(stage->draw);
58
59   /* Window coords: */
60   const float *v0 = header->v[0]->data[pos];
61   const float *v1 = header->v[1]->data[pos];
62   const float *v2 = header->v[2]->data[pos];
63
64   /* edge vectors: e = v0 - v2, f = v1 - v2 */
65   const float ex = v0[0] - v2[0];
66   const float ey = v0[1] - v2[1];
67   const float fx = v1[0] - v2[0];
68   const float fy = v1[1] - v2[1];
69
70   /* det = cross(e,f).z */
71   header->det = ex * fy - ey * fx;
72
73   if (header->det != 0) {
74      /* if det < 0 then Z points toward the camera and the triangle is
75       * counter-clockwise winding.
76       */
77      unsigned ccw = (header->det < 0);
78      unsigned face = ((ccw == cull_stage(stage)->front_ccw) ?
79                       PIPE_FACE_FRONT :
80                       PIPE_FACE_BACK);
81
82      if ((face & cull_stage(stage)->cull_face) == 0) {
83         /* triangle is not culled, pass to next stage */
84	 stage->next->tri( stage->next, header );
85      }
86   }
87}
88
89
90static void cull_first_tri( struct draw_stage *stage,
91			    struct prim_header *header )
92{
93   struct cull_stage *cull = cull_stage(stage);
94
95   cull->cull_face = stage->draw->rasterizer->cull_face;
96   cull->front_ccw = stage->draw->rasterizer->front_ccw;
97
98   stage->tri = cull_tri;
99   stage->tri( stage, header );
100}
101
102
103static void cull_flush( struct draw_stage *stage, unsigned flags )
104{
105   stage->tri = cull_first_tri;
106   stage->next->flush( stage->next, flags );
107}
108
109
110static void cull_reset_stipple_counter( struct draw_stage *stage )
111{
112   stage->next->reset_stipple_counter( stage->next );
113}
114
115
116static void cull_destroy( struct draw_stage *stage )
117{
118   draw_free_temp_verts( stage );
119   FREE( stage );
120}
121
122
123/**
124 * Create a new polygon culling stage.
125 */
126struct draw_stage *draw_cull_stage( struct draw_context *draw )
127{
128   struct cull_stage *cull = CALLOC_STRUCT(cull_stage);
129   if (cull == NULL)
130      goto fail;
131
132   cull->stage.draw = draw;
133   cull->stage.name = "cull";
134   cull->stage.next = NULL;
135   cull->stage.point = draw_pipe_passthrough_point;
136   cull->stage.line = draw_pipe_passthrough_line;
137   cull->stage.tri = cull_first_tri;
138   cull->stage.flush = cull_flush;
139   cull->stage.reset_stipple_counter = cull_reset_stipple_counter;
140   cull->stage.destroy = cull_destroy;
141
142   if (!draw_alloc_temp_verts( &cull->stage, 0 ))
143      goto fail;
144
145   return &cull->stage;
146
147fail:
148   if (cull)
149      cull->stage.destroy( &cull->stage );
150
151   return NULL;
152}
153