src/gallium/auxiliary/draw/draw_pipe_cull.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
   4  * All Rights Reserved.
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  11  * permit persons to whom the Software is furnished to do so, subject to
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  15  * next paragraph) shall be included in all copies or substantial portions
  16  * of the Software.
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  27
  28 /**
  29  * \brief  Drawing stage for polygon culling
  30  */
  31
  32 /* Authors:  Keith Whitwell <keith@tungstengraphics.com>
  33  */
  34
  35
  36 #include "pipe/p_util.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 winding;  /**< which winding(s) to cull (one of PIPE_WINDING_x) */
  44 };
  45
  46
  47 static INLINE struct cull_stage *cull_stage( struct draw_stage *stage )
  48 {
  49    return (struct cull_stage *)stage;
  50 }
  51
  52
  53
  54
  55 static void cull_tri( struct draw_stage *stage,
  56                       struct prim_header *header )
  57 {
  58    /* Window coords: */
  59    const float *v0 = header->v[0]->data[0];
  60    const float *v1 = header->v[1]->data[0];
  61    const float *v2 = header->v[2]->data[0];
  62
  63    /* edge vectors e = v0 - v2, f = v1 - v2 */
  64    const float ex = v0[0] - v2[0];
  65    const float ey = v0[1] - v2[1];
  66    const float fx = v1[0] - v2[0];
  67    const float fy = v1[1] - v2[1];
  68
  69    /* det = cross(e,f).z */
  70    header->det = ex * fy - ey * fx;
  71
  72    if (header->det != 0) {
  73       /* if (det < 0 then Z points toward camera and triangle is
  74        * counter-clockwise winding.
  75        */
  76       unsigned winding = (header->det < 0) ? PIPE_WINDING_CCW : PIPE_WINDING_CW;
  77
  78       if ((winding & cull_stage(stage)->winding) == 0) {
  79          /* triangle is not culled, pass to next stage */
  80          stage->next->tri( stage->next, header );
  81       }
  82    }
  83 }
  84
  85 static void cull_first_tri( struct draw_stage *stage,
  86                             struct prim_header *header )
  87 {
  88    struct cull_stage *cull = cull_stage(stage);
  89
  90    cull->winding = stage->draw->rasterizer->cull_mode;
  91
  92    stage->tri = cull_tri;
  93    stage->tri( stage, header );
  94 }
  95
  96
  97
  98 static void cull_flush( struct draw_stage *stage, unsigned flags )
  99 {
 100    stage->tri = cull_first_tri;
 101    stage->next->flush( stage->next, flags );
 102 }
 103
 104 static void cull_reset_stipple_counter( struct draw_stage *stage )
 105 {
 106    stage->next->reset_stipple_counter( stage->next );
 107 }
 108
 109
 110 static void cull_destroy( struct draw_stage *stage )
 111 {
 112    draw_free_temp_verts( stage );
 113    FREE( stage );
 114 }
 115
 116
 117 /**
 118  * Create a new polygon culling stage.
 119  */
 120 struct draw_stage *draw_cull_stage( struct draw_context *draw )
 121 {
 122    struct cull_stage *cull = CALLOC_STRUCT(cull_stage);
 123
 124    draw_alloc_temp_verts( &cull->stage, 0 );
 125
 126    cull->stage.draw = draw;
 127    cull->stage.next = NULL;
 128    cull->stage.point = draw_pipe_passthrough_point;
 129    cull->stage.line = draw_pipe_passthrough_line;
 130    cull->stage.tri = cull_first_tri;
 131    cull->stage.flush = cull_flush;
 132    cull->stage.reset_stipple_counter = cull_reset_stipple_counter;
 133    cull->stage.destroy = cull_destroy;
 134
 135    return &cull->stage;
 136 }