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
42 struct 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
cull_stage(struct draw_stage * stage)49 static 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 */
cull_tri(struct draw_stage * stage,struct prim_header * header)57 static 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
cull_first_tri(struct draw_stage * stage,struct prim_header * header)105 static 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
cull_flush(struct draw_stage * stage,unsigned flags)118 static 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
cull_reset_stipple_counter(struct draw_stage * stage)125 static void cull_reset_stipple_counter( struct draw_stage *stage )
126 {
127 stage->next->reset_stipple_counter( stage->next );
128 }
129
130
cull_destroy(struct draw_stage * stage)131 static 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 */
draw_cull_stage(struct draw_context * draw)141 struct 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
162 fail:
163 if (cull)
164 cull->stage.destroy( &cull->stage );
165
166 return NULL;
167 }
168