workbench/libs/mesa/src/gallium/auxiliary/draw/draw_pipe_cull.c

   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
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  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
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  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
  41 struct 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
  48 static INLINE struct cull_stage *cull_stage( struct draw_stage *stage )
  49 {
  50    return (struct cull_stage *)stage;
  51 }
  52
  53
  54 static 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
  90 static 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
 103 static 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
 110 static void cull_reset_stipple_counter( struct draw_stage *stage )
 111 {
 112    stage->next->reset_stipple_counter( stage->next );
 113 }
 114
 115
 116 static 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  */
 126 struct 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
 147 fail:
 148    if (cull)
 149       cull->stage.destroy( &cull->stage );
 150
 151    return NULL;
 152 }