src/gallium/auxiliary/draw/draw_pipe_cull.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
   4  * All Rights Reserved.
   5  *
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  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
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  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
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  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 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    const unsigned pos = stage->draw->vs.position_output;
  59
  60    /* Window coords: */
  61    const float *v0 = header->v[0]->data[pos];
  62    const float *v1 = header->v[1]->data[pos];
  63    const float *v2 = header->v[2]->data[pos];
  64
  65    /* edge vectors e = v0 - v2, f = v1 - v2 */
  66    const float ex = v0[0] - v2[0];
  67    const float ey = v0[1] - v2[1];
  68    const float fx = v1[0] - v2[0];
  69    const float fy = v1[1] - v2[1];
  70
  71    /* det = cross(e,f).z */
  72    header->det = ex * fy - ey * fx;
  73
  74    if (header->det != 0) {
  75       /* if (det < 0 then Z points toward camera and triangle is
  76        * counter-clockwise winding.
  77        */
  78       unsigned winding = (header->det < 0) ? PIPE_WINDING_CCW : PIPE_WINDING_CW;
  79
  80       if ((winding & cull_stage(stage)->winding) == 0) {
  81          /* triangle is not culled, pass to next stage */
  82          stage->next->tri( stage->next, header );
  83       }
  84    }
  85 }
  86
  87 static void cull_first_tri( struct draw_stage *stage,
  88                             struct prim_header *header )
  89 {
  90    struct cull_stage *cull = cull_stage(stage);
  91
  92    cull->winding = stage->draw->rasterizer->cull_mode;
  93
  94    stage->tri = cull_tri;
  95    stage->tri( stage, header );
  96 }
  97
  98
  99
 100 static void cull_flush( struct draw_stage *stage, unsigned flags )
 101 {
 102    stage->tri = cull_first_tri;
 103    stage->next->flush( stage->next, flags );
 104 }
 105
 106 static void cull_reset_stipple_counter( struct draw_stage *stage )
 107 {
 108    stage->next->reset_stipple_counter( stage->next );
 109 }
 110
 111
 112 static void cull_destroy( struct draw_stage *stage )
 113 {
 114    draw_free_temp_verts( stage );
 115    FREE( stage );
 116 }
 117
 118
 119 /**
 120  * Create a new polygon culling stage.
 121  */
 122 struct draw_stage *draw_cull_stage( struct draw_context *draw )
 123 {
 124    struct cull_stage *cull = CALLOC_STRUCT(cull_stage);
 125    if (cull == NULL)
 126       goto fail;
 127
 128    if (!draw_alloc_temp_verts( &cull->stage, 0 ))
 129       goto fail;
 130
 131    cull->stage.draw = draw;
 132    cull->stage.next = NULL;
 133    cull->stage.point = draw_pipe_passthrough_point;
 134    cull->stage.line = draw_pipe_passthrough_line;
 135    cull->stage.tri = cull_first_tri;
 136    cull->stage.flush = cull_flush;
 137    cull->stage.reset_stipple_counter = cull_reset_stipple_counter;
 138    cull->stage.destroy = cull_destroy;
 139
 140    return &cull->stage;
 141
 142  fail:
 143    if (cull)
 144       cull->stage.destroy( &cull->stage );
 145
 146    return NULL;
 147 }