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 <[email protected]>
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
49 static inline struct cull_stage *
cull_stage(struct draw_stage * stage)50 cull_stage(struct draw_stage *stage)
51 {
52 return (struct cull_stage *)stage;
53 }
54
55 /*
56 * Triangles can be culled using regular face cull.
57 */
58 static void
cull_tri(struct draw_stage * stage,struct prim_header * header)59 cull_tri(struct draw_stage *stage,
60 struct prim_header *header)
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 /* det = cross(e,f).z */
75 header->det = ex * fy - ey * fx;
76
77 if (header->det != 0) {
78 /* if det < 0 then Z points toward the camera and the triangle is
79 * counter-clockwise winding.
80 */
81 unsigned ccw = (header->det < 0);
82 unsigned face = ((ccw == cull_stage(stage)->front_ccw) ?
83 PIPE_FACE_FRONT :
84 PIPE_FACE_BACK);
85
86 if ((face & cull_stage(stage)->cull_face) == 0) {
87 /* triangle is not culled, pass to next stage */
88 stage->next->tri(stage->next, header);
89 }
90 } else {
91 /*
92 * With zero area, this is back facing (because the spec says
93 * it's front facing if sign is positive?).
94 * Some apis apparently do not allow us to cull zero area tris
95 * here, in case of fill mode line (which is rather lame).
96 */
97 if ((PIPE_FACE_BACK & cull_stage(stage)->cull_face) == 0) {
98 stage->next->tri(stage->next, header);
99 }
100 }
101 }
102
103
104 static void
cull_first_tri(struct draw_stage * stage,struct prim_header * header)105 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
118 static void
cull_flush(struct draw_stage * stage,unsigned flags)119 cull_flush(struct draw_stage *stage, unsigned flags)
120 {
121 stage->tri = cull_first_tri;
122 stage->next->flush(stage->next, flags);
123 }
124
125
126 static void
cull_reset_stipple_counter(struct draw_stage * stage)127 cull_reset_stipple_counter(struct draw_stage *stage)
128 {
129 stage->next->reset_stipple_counter(stage->next);
130 }
131
132
133 static void
cull_destroy(struct draw_stage * stage)134 cull_destroy(struct draw_stage *stage)
135 {
136 draw_free_temp_verts(stage);
137 FREE(stage);
138 }
139
140
141 /**
142 * Create a new polygon culling stage.
143 */
144 struct draw_stage *
draw_cull_stage(struct draw_context * draw)145 draw_cull_stage(struct draw_context *draw)
146 {
147 struct cull_stage *cull = CALLOC_STRUCT(cull_stage);
148 if (!cull)
149 goto fail;
150
151 cull->stage.draw = draw;
152 cull->stage.name = "cull";
153 cull->stage.next = NULL;
154 cull->stage.point = draw_pipe_passthrough_point;
155 cull->stage.line = draw_pipe_passthrough_line;
156 cull->stage.tri = cull_first_tri;
157 cull->stage.flush = cull_flush;
158 cull->stage.reset_stipple_counter = cull_reset_stipple_counter;
159 cull->stage.destroy = cull_destroy;
160
161 if (!draw_alloc_temp_verts(&cull->stage, 0))
162 goto fail;
163
164 return &cull->stage;
165
166 fail:
167 if (cull)
168 cull->stage.destroy(&cull->stage);
169
170 return NULL;
171 }
172