src/gallium/auxiliary/draw/draw_pipe_cull.c

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   3  * Copyright 2007 VMware, Inc.
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  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
  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  */
  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
 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
 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
 125 static void cull_reset_stipple_counter( struct draw_stage *stage )
 126 {
 127    stage->next->reset_stipple_counter( stage->next );
 128 }
 129
 130
 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  */
 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 }