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 static inline boolean
  55 cull_distance_is_out(float dist)
  56 {
  57    return (dist < 0.0f) || util_is_inf_or_nan(dist);
  58 }
  59
  60 /*
  61  * If the shader writes the culldistance then we can
  62  * perform distance based culling. Distance based
  63  * culling doesn't require a face and can be performed
  64  * on primitives without faces (e.g. points and lines)
  65  */
  66 static void cull_point( struct draw_stage *stage,
  67                         struct prim_header *header )
  68 {
  69    const unsigned num_written_culldistances =
  70       draw_current_shader_num_written_culldistances(stage->draw);
  71    const unsigned num_written_clipdistances =
  72       draw_current_shader_num_written_clipdistances(stage->draw);
  73    unsigned i;
  74
  75    debug_assert(num_written_culldistances);
  76
  77    for (i = 0; i < num_written_culldistances; ++i) {
  78       unsigned cull_idx = (num_written_clipdistances + i) / 4;
  79       unsigned out_idx =
  80          draw_current_shader_ccdistance_output(stage->draw, cull_idx);
  81       unsigned idx = (num_written_clipdistances + i) % 4;
  82       float cull1 = header->v[0]->data[out_idx][idx];
  83       boolean vert1_out = cull_distance_is_out(cull1);
  84       if (vert1_out)
  85          return;
  86    }
  87    stage->next->point( stage->next, header );
  88 }
  89
  90 /*
  91  * If the shader writes the culldistance then we can
  92  * perform distance based culling. Distance based
  93  * culling doesn't require a face and can be performed
  94  * on primitives without faces (e.g. points and lines)
  95  */
  96 static void cull_line( struct draw_stage *stage,
  97                        struct prim_header *header )
  98 {
  99    const unsigned num_written_culldistances =
 100       draw_current_shader_num_written_culldistances(stage->draw);
 101    const unsigned num_written_clipdistances =
 102       draw_current_shader_num_written_clipdistances(stage->draw);
 103    unsigned i;
 104
 105    debug_assert(num_written_culldistances);
 106
 107    for (i = 0; i < num_written_culldistances; ++i) {
 108       unsigned cull_idx = (num_written_clipdistances + i) / 4;
 109       unsigned out_idx =
 110          draw_current_shader_ccdistance_output(stage->draw, cull_idx);
 111       unsigned idx = (num_written_clipdistances + i) % 4;
 112       float cull1 = header->v[0]->data[out_idx][idx];
 113       float cull2 = header->v[1]->data[out_idx][idx];
 114       boolean vert1_out = cull_distance_is_out(cull1);
 115       boolean vert2_out = cull_distance_is_out(cull2);
 116       if (vert1_out && vert2_out)
 117          return;
 118    }
 119    stage->next->line( stage->next, header );
 120 }
 121
 122 /*
 123  * Triangles can be culled either using the cull distance
 124  * shader outputs or the regular face culling. If required
 125  * this function performs both, starting with distance culling.
 126  */
 127 static void cull_tri( struct draw_stage *stage,
 128                       struct prim_header *header )
 129 {
 130    const unsigned num_written_culldistances =
 131       draw_current_shader_num_written_culldistances(stage->draw);
 132    const unsigned num_written_clipdistances =
 133       draw_current_shader_num_written_clipdistances(stage->draw);
 134    /* Do the distance culling */
 135    if (num_written_culldistances) {
 136       unsigned i;
 137       for (i = 0; i < num_written_culldistances; ++i) {
 138          unsigned cull_idx = (num_written_clipdistances + i) / 4;
 139          unsigned out_idx =
 140             draw_current_shader_ccdistance_output(stage->draw, cull_idx);
 141          unsigned idx = (num_written_clipdistances + i) % 4;
 142          float cull1 = header->v[0]->data[out_idx][idx];
 143          float cull2 = header->v[1]->data[out_idx][idx];
 144          float cull3 = header->v[2]->data[out_idx][idx];
 145          boolean vert1_out = cull_distance_is_out(cull1);
 146          boolean vert2_out = cull_distance_is_out(cull2);
 147          boolean vert3_out = cull_distance_is_out(cull3);
 148          if (vert1_out && vert2_out && vert3_out)
 149             return;
 150       }
 151    }
 152
 153    /* Do the regular face culling */
 154    {
 155       const unsigned pos = draw_current_shader_position_output(stage->draw);
 156       /* Window coords: */
 157       const float *v0 = header->v[0]->data[pos];
 158       const float *v1 = header->v[1]->data[pos];
 159       const float *v2 = header->v[2]->data[pos];
 160
 161       /* edge vectors: e = v0 - v2, f = v1 - v2 */
 162       const float ex = v0[0] - v2[0];
 163       const float ey = v0[1] - v2[1];
 164       const float fx = v1[0] - v2[0];
 165       const float fy = v1[1] - v2[1];
 166
 167
 168       /* det = cross(e,f).z */
 169       header->det = ex * fy - ey * fx;
 170
 171       if (header->det != 0) {
 172          /* if det < 0 then Z points toward the camera and the triangle is
 173           * counter-clockwise winding.
 174           */
 175          unsigned ccw = (header->det < 0);
 176          unsigned face = ((ccw == cull_stage(stage)->front_ccw) ?
 177                           PIPE_FACE_FRONT :
 178                           PIPE_FACE_BACK);
 179
 180          if ((face & cull_stage(stage)->cull_face) == 0) {
 181             /* triangle is not culled, pass to next stage */
 182             stage->next->tri( stage->next, header );
 183          }
 184       }
 185    }
 186 }
 187
 188 static void cull_first_point( struct draw_stage *stage,
 189                               struct prim_header *header )
 190 {
 191    const unsigned num_written_culldistances =
 192       draw_current_shader_num_written_culldistances(stage->draw);
 193
 194    if (num_written_culldistances) {
 195       stage->point = cull_point;
 196       stage->point( stage, header );
 197    } else {
 198       stage->point = draw_pipe_passthrough_point;
 199       stage->point( stage, header );
 200    }
 201 }
 202
 203 static void cull_first_line( struct draw_stage *stage,
 204                             struct prim_header *header )
 205 {
 206    const unsigned num_written_culldistances =
 207       draw_current_shader_num_written_culldistances(stage->draw);
 208
 209    if (num_written_culldistances) {
 210       stage->line = cull_line;
 211       stage->line( stage, header );
 212    } else {
 213       stage->line = draw_pipe_passthrough_line;
 214       stage->line( stage, header );
 215    }
 216 }
 217
 218 static void cull_first_tri( struct draw_stage *stage,
 219                             struct prim_header *header )
 220 {
 221    struct cull_stage *cull = cull_stage(stage);
 222
 223    cull->cull_face = stage->draw->rasterizer->cull_face;
 224    cull->front_ccw = stage->draw->rasterizer->front_ccw;
 225
 226    stage->tri = cull_tri;
 227    stage->tri( stage, header );
 228 }
 229
 230
 231 static void cull_flush( struct draw_stage *stage, unsigned flags )
 232 {
 233    stage->point = cull_first_point;
 234    stage->line = cull_first_line;
 235    stage->tri = cull_first_tri;
 236    stage->next->flush( stage->next, flags );
 237 }
 238
 239
 240 static void cull_reset_stipple_counter( struct draw_stage *stage )
 241 {
 242    stage->next->reset_stipple_counter( stage->next );
 243 }
 244
 245
 246 static void cull_destroy( struct draw_stage *stage )
 247 {
 248    draw_free_temp_verts( stage );
 249    FREE( stage );
 250 }
 251
 252
 253 /**
 254  * Create a new polygon culling stage.
 255  */
 256 struct draw_stage *draw_cull_stage( struct draw_context *draw )
 257 {
 258    struct cull_stage *cull = CALLOC_STRUCT(cull_stage);
 259    if (!cull)
 260       goto fail;
 261
 262    cull->stage.draw = draw;
 263    cull->stage.name = "cull";
 264    cull->stage.next = NULL;
 265    cull->stage.point = cull_first_point;
 266    cull->stage.line = cull_first_line;
 267    cull->stage.tri = cull_first_tri;
 268    cull->stage.flush = cull_flush;
 269    cull->stage.reset_stipple_counter = cull_reset_stipple_counter;
 270    cull->stage.destroy = cull_destroy;
 271
 272    if (!draw_alloc_temp_verts( &cull->stage, 0 ))
 273       goto fail;
 274
 275    return &cull->stage;
 276
 277 fail:
 278    if (cull)
 279       cull->stage.destroy( &cull->stage );
 280
 281    return NULL;
 282 }