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