1/**************************************************************************
2 *
3 * Copyright 2007 VMware, Inc.
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 VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
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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 <keithw@vmware.com>
33 */
34
35
36#include "util/u_math.h"
37#include "util/u_memory.h"
38#include "pipe/p_defines.h"
39#include "draw_pipe.h"
40
41
42struct cull_stage {
43   struct draw_stage stage;
44   unsigned cull_face;  /**< which face(s) to cull (one of PIPE_FACE_x) */
45   unsigned front_ccw;
46};
47
48
49static inline struct cull_stage *cull_stage( struct draw_stage *stage )
50{
51   return (struct cull_stage *)stage;
52}
53
54/*
55 * Triangles can be culled using regular face cull.
56 */
57static void cull_tri( struct draw_stage *stage,
58		      struct prim_header *header )
59{
60   /* Do the regular face culling */
61   {
62      const unsigned pos = draw_current_shader_position_output(stage->draw);
63      /* Window coords: */
64      const float *v0 = header->v[0]->data[pos];
65      const float *v1 = header->v[1]->data[pos];
66      const float *v2 = header->v[2]->data[pos];
67
68      /* edge vectors: e = v0 - v2, f = v1 - v2 */
69      const float ex = v0[0] - v2[0];
70      const float ey = v0[1] - v2[1];
71      const float fx = v1[0] - v2[0];
72      const float fy = v1[1] - v2[1];
73
74
75      /* det = cross(e,f).z */
76      header->det = ex * fy - ey * fx;
77
78      if (header->det != 0) {
79         /* if det < 0 then Z points toward the camera and the triangle is
80          * counter-clockwise winding.
81          */
82         unsigned ccw = (header->det < 0);
83         unsigned face = ((ccw == cull_stage(stage)->front_ccw) ?
84                          PIPE_FACE_FRONT :
85                          PIPE_FACE_BACK);
86
87         if ((face & cull_stage(stage)->cull_face) == 0) {
88            /* triangle is not culled, pass to next stage */
89            stage->next->tri( stage->next, header );
90         }
91      } else {
92         /*
93          * With zero area, this is back facing (because the spec says
94          * it's front facing if sign is positive?).
95          * Some apis apparently do not allow us to cull zero area tris
96          * here, in case of fill mode line (which is rather lame).
97          */
98         if ((PIPE_FACE_BACK & cull_stage(stage)->cull_face) == 0) {
99            stage->next->tri( stage->next, header );
100         }
101      }
102   }
103}
104
105static void cull_first_tri( struct draw_stage *stage,
106			    struct prim_header *header )
107{
108   struct cull_stage *cull = cull_stage(stage);
109
110   cull->cull_face = stage->draw->rasterizer->cull_face;
111   cull->front_ccw = stage->draw->rasterizer->front_ccw;
112
113   stage->tri = cull_tri;
114   stage->tri( stage, header );
115}
116
117
118static void cull_flush( struct draw_stage *stage, unsigned flags )
119{
120   stage->tri = cull_first_tri;
121   stage->next->flush( stage->next, flags );
122}
123
124
125static void cull_reset_stipple_counter( struct draw_stage *stage )
126{
127   stage->next->reset_stipple_counter( stage->next );
128}
129
130
131static void cull_destroy( struct draw_stage *stage )
132{
133   draw_free_temp_verts( stage );
134   FREE( stage );
135}
136
137
138/**
139 * Create a new polygon culling stage.
140 */
141struct draw_stage *draw_cull_stage( struct draw_context *draw )
142{
143   struct cull_stage *cull = CALLOC_STRUCT(cull_stage);
144   if (!cull)
145      goto fail;
146
147   cull->stage.draw = draw;
148   cull->stage.name = "cull";
149   cull->stage.next = NULL;
150   cull->stage.point = draw_pipe_passthrough_point;
151   cull->stage.line = draw_pipe_passthrough_line;
152   cull->stage.tri = cull_first_tri;
153   cull->stage.flush = cull_flush;
154   cull->stage.reset_stipple_counter = cull_reset_stipple_counter;
155   cull->stage.destroy = cull_destroy;
156
157   if (!draw_alloc_temp_verts( &cull->stage, 0 ))
158      goto fail;
159
160   return &cull->stage;
161
162fail:
163   if (cull)
164      cull->stage.destroy( &cull->stage );
165
166   return NULL;
167}
168