src/gallium/drivers/llvmpipe/lp_setup_tri.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
   4  * All Rights Reserved.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a
   7  * copy of this software and associated documentation files (the
   8  * "Software"), to deal in the Software without restriction, including
   9  * without limitation the rights to use, copy, modify, merge, publish,
  10  * distribute, sub license, and/or sell copies of the Software, and to
  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
  13  *
  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
  19  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  20  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  21  * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS BE LIABLE FOR
  22  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  23  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  24  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  **************************************************************************/
  27
  28 /*
  29  * Binning code for triangles
  30  */
  31
  32 #include "util/u_math.h"
  33 #include "util/u_memory.h"
  34 #include "lp_perf.h"
  35 #include "lp_setup_context.h"
  36 #include "lp_rast.h"
  37
  38 #define NUM_CHANNELS 4
  39
  40
  41 /**
  42  * Compute a0 for a constant-valued coefficient (GL_FLAT shading).
  43  */
  44 static void constant_coef( struct lp_setup_context *setup,
  45                            struct lp_rast_triangle *tri,
  46                            unsigned slot,
  47                            const float value,
  48                            unsigned i )
  49 {
  50    tri->inputs.a0[slot][i] = value;
  51    tri->inputs.dadx[slot][i] = 0.0f;
  52    tri->inputs.dady[slot][i] = 0.0f;
  53 }
  54
  55
  56 /**
  57  * Compute a0, dadx and dady for a linearly interpolated coefficient,
  58  * for a triangle.
  59  */
  60 static void linear_coef( struct lp_setup_context *setup,
  61                          struct lp_rast_triangle *tri,
  62                          float oneoverarea,
  63                          unsigned slot,
  64                          const float (*v1)[4],
  65                          const float (*v2)[4],
  66                          const float (*v3)[4],
  67                          unsigned vert_attr,
  68                          unsigned i)
  69 {
  70    float a1 = v1[vert_attr][i];
  71    float a2 = v2[vert_attr][i];
  72    float a3 = v3[vert_attr][i];
  73
  74    float da12 = a1 - a2;
  75    float da31 = a3 - a1;
  76    float dadx = (da12 * tri->dy31 - tri->dy12 * da31) * oneoverarea;
  77    float dady = (da31 * tri->dx12 - tri->dx31 * da12) * oneoverarea;
  78
  79    tri->inputs.dadx[slot][i] = dadx;
  80    tri->inputs.dady[slot][i] = dady;
  81
  82    /* calculate a0 as the value which would be sampled for the
  83     * fragment at (0,0), taking into account that we want to sample at
  84     * pixel centers, in other words (0.5, 0.5).
  85     *
  86     * this is neat but unfortunately not a good way to do things for
  87     * triangles with very large values of dadx or dady as it will
  88     * result in the subtraction and re-addition from a0 of a very
  89     * large number, which means we'll end up loosing a lot of the
  90     * fractional bits and precision from a0.  the way to fix this is
  91     * to define a0 as the sample at a pixel center somewhere near vmin
  92     * instead - i'll switch to this later.
  93     */
  94    tri->inputs.a0[slot][i] = (a1 -
  95                               (dadx * (v1[0][0] - setup->pixel_offset) +
  96                                dady * (v1[0][1] - setup->pixel_offset)));
  97 }
  98
  99
 100 /**
 101  * Compute a0, dadx and dady for a perspective-corrected interpolant,
 102  * for a triangle.
 103  * We basically multiply the vertex value by 1/w before computing
 104  * the plane coefficients (a0, dadx, dady).
 105  * Later, when we compute the value at a particular fragment position we'll
 106  * divide the interpolated value by the interpolated W at that fragment.
 107  */
 108 static void perspective_coef( struct lp_setup_context *setup,
 109                               struct lp_rast_triangle *tri,
 110                               float oneoverarea,
 111                               unsigned slot,
 112                               const float (*v1)[4],
 113                               const float (*v2)[4],
 114                               const float (*v3)[4],
 115                               unsigned vert_attr,
 116                               unsigned i)
 117 {
 118    /* premultiply by 1/w  (v[0][3] is always 1/w):
 119     */
 120    float a1 = v1[vert_attr][i] * v1[0][3];
 121    float a2 = v2[vert_attr][i] * v2[0][3];
 122    float a3 = v3[vert_attr][i] * v3[0][3];
 123    float da12 = a1 - a2;
 124    float da31 = a3 - a1;
 125    float dadx = (da12 * tri->dy31 - tri->dy12 * da31) * oneoverarea;
 126    float dady = (da31 * tri->dx12 - tri->dx31 * da12) * oneoverarea;
 127
 128    tri->inputs.dadx[slot][i] = dadx;
 129    tri->inputs.dady[slot][i] = dady;
 130    tri->inputs.a0[slot][i] = (a1 -
 131                               (dadx * (v1[0][0] - setup->pixel_offset) +
 132                                dady * (v1[0][1] - setup->pixel_offset)));
 133 }
 134
 135
 136 /**
 137  * Special coefficient setup for gl_FragCoord.
 138  * X and Y are trivial
 139  * Z and W are copied from position_coef which should have already been computed.
 140  * We could do a bit less work if we'd examine gl_FragCoord's swizzle mask.
 141  */
 142 static void
 143 setup_fragcoord_coef(struct lp_setup_context *setup,
 144                      struct lp_rast_triangle *tri,
 145                      float oneoverarea,
 146                      unsigned slot,
 147                      const float (*v1)[4],
 148                      const float (*v2)[4],
 149                      const float (*v3)[4])
 150 {
 151    /*X*/
 152    tri->inputs.a0[slot][0] = 0.0;
 153    tri->inputs.dadx[slot][0] = 1.0;
 154    tri->inputs.dady[slot][0] = 0.0;
 155    /*Y*/
 156    tri->inputs.a0[slot][1] = 0.0;
 157    tri->inputs.dadx[slot][1] = 0.0;
 158    tri->inputs.dady[slot][1] = 1.0;
 159    /*Z*/
 160    linear_coef(setup, tri, oneoverarea, slot, v1, v2, v3, 0, 2);
 161    /*W*/
 162    linear_coef(setup, tri, oneoverarea, slot, v1, v2, v3, 0, 3);
 163 }
 164
 165
 166 static void setup_facing_coef( struct lp_setup_context *setup,
 167                                struct lp_rast_triangle *tri,
 168                                unsigned slot,
 169                                boolean frontface )
 170 {
 171    constant_coef( setup, tri, slot, 1.0f - frontface, 0 );
 172    constant_coef( setup, tri, slot, 0.0f, 1 ); /* wasted */
 173    constant_coef( setup, tri, slot, 0.0f, 2 ); /* wasted */
 174    constant_coef( setup, tri, slot, 0.0f, 3 ); /* wasted */
 175 }
 176
 177
 178 /**
 179  * Compute the tri->coef[] array dadx, dady, a0 values.
 180  */
 181 static void setup_tri_coefficients( struct lp_setup_context *setup,
 182                                     struct lp_rast_triangle *tri,
 183                                     float oneoverarea,
 184                                     const float (*v1)[4],
 185                                     const float (*v2)[4],
 186                                     const float (*v3)[4],
 187                                     boolean frontface)
 188 {
 189    unsigned slot;
 190
 191    /* The internal position input is in slot zero:
 192     */
 193    setup_fragcoord_coef(setup, tri, oneoverarea, 0, v1, v2, v3);
 194
 195    /* setup interpolation for all the remaining attributes:
 196     */
 197    for (slot = 0; slot < setup->fs.nr_inputs; slot++) {
 198       unsigned vert_attr = setup->fs.input[slot].src_index;
 199       unsigned i;
 200
 201       switch (setup->fs.input[slot].interp) {
 202       case LP_INTERP_CONSTANT:
 203          for (i = 0; i < NUM_CHANNELS; i++)
 204             constant_coef(setup, tri, slot+1, v3[vert_attr][i], i);
 205          break;
 206
 207       case LP_INTERP_LINEAR:
 208          for (i = 0; i < NUM_CHANNELS; i++)
 209             linear_coef(setup, tri, oneoverarea, slot+1, v1, v2, v3, vert_attr, i);
 210          break;
 211
 212       case LP_INTERP_PERSPECTIVE:
 213          for (i = 0; i < NUM_CHANNELS; i++)
 214             perspective_coef(setup, tri, oneoverarea, slot+1, v1, v2, v3, vert_attr, i);
 215          break;
 216
 217       case LP_INTERP_POSITION:
 218          /* XXX: fix me - duplicates the values in slot zero.
 219           */
 220          setup_fragcoord_coef(setup, tri, oneoverarea, slot+1, v1, v2, v3);
 221          break;
 222
 223       case LP_INTERP_FACING:
 224          setup_facing_coef(setup, tri, slot+1, frontface);
 225          break;
 226
 227       default:
 228          assert(0);
 229       }
 230    }
 231 }
 232
 233
 234
 235 static INLINE int subpixel_snap( float a )
 236 {
 237    return util_iround(FIXED_ONE * a - (FIXED_ONE / 2));
 238 }
 239
 240
 241
 242 /**
 243  * Alloc space for a new triangle plus the input.a0/dadx/dady arrays
 244  * immediately after it.
 245  * The memory is allocated from the per-scene pool, not per-tile.
 246  * \param tri_size  returns number of bytes allocated
 247  * \param nr_inputs  number of fragment shader inputs
 248  * \return pointer to triangle space
 249  */
 250 static INLINE struct lp_rast_triangle *
 251 alloc_triangle(struct lp_scene *scene, unsigned nr_inputs, unsigned *tri_size)
 252 {
 253    unsigned input_array_sz = NUM_CHANNELS * (nr_inputs + 1) * sizeof(float);
 254    struct lp_rast_triangle *tri;
 255    unsigned bytes;
 256    char *inputs;
 257
 258    assert(sizeof(*tri) % 16 == 0);
 259
 260    bytes = sizeof(*tri) + (3 * input_array_sz);
 261
 262    tri = lp_scene_alloc_aligned( scene, bytes, 16 );
 263
 264    inputs = (char *) (tri + 1);
 265    tri->inputs.a0   = (float (*)[4]) inputs;
 266    tri->inputs.dadx = (float (*)[4]) (inputs + input_array_sz);
 267    tri->inputs.dady = (float (*)[4]) (inputs + 2 * input_array_sz);
 268
 269    *tri_size = bytes;
 270
 271    return tri;
 272 }
 273
 274
 275
 276 /**
 277  * Do basic setup for triangle rasterization and determine which
 278  * framebuffer tiles are touched.  Put the triangle in the scene's
 279  * bins for the tiles which we overlap.
 280  */
 281 static void
 282 do_triangle_ccw(struct lp_setup_context *setup,
 283                 const float (*v1)[4],
 284                 const float (*v2)[4],
 285                 const float (*v3)[4],
 286                 boolean frontfacing )
 287 {
 288    /* x/y positions in fixed point */
 289    const int x1 = subpixel_snap(v1[0][0] + 0.5 - setup->pixel_offset);
 290    const int x2 = subpixel_snap(v2[0][0] + 0.5 - setup->pixel_offset);
 291    const int x3 = subpixel_snap(v3[0][0] + 0.5 - setup->pixel_offset);
 292    const int y1 = subpixel_snap(v1[0][1] + 0.5 - setup->pixel_offset);
 293    const int y2 = subpixel_snap(v2[0][1] + 0.5 - setup->pixel_offset);
 294    const int y3 = subpixel_snap(v3[0][1] + 0.5 - setup->pixel_offset);
 295
 296    struct lp_scene *scene = lp_setup_get_current_scene(setup);
 297    struct lp_rast_triangle *tri;
 298    int area;
 299    float oneoverarea;
 300    int minx, maxx, miny, maxy;
 301    unsigned tri_bytes;
 302
 303    tri = alloc_triangle(scene, setup->fs.nr_inputs, &tri_bytes);
 304
 305 #ifdef DEBUG
 306    tri->v[0][0] = v1[0][0];
 307    tri->v[1][0] = v2[0][0];
 308    tri->v[2][0] = v3[0][0];
 309    tri->v[0][1] = v1[0][1];
 310    tri->v[1][1] = v2[0][1];
 311    tri->v[2][1] = v3[0][1];
 312 #endif
 313
 314    tri->dx12 = x1 - x2;
 315    tri->dx23 = x2 - x3;
 316    tri->dx31 = x3 - x1;
 317
 318    tri->dy12 = y1 - y2;
 319    tri->dy23 = y2 - y3;
 320    tri->dy31 = y3 - y1;
 321
 322    area = (tri->dx12 * tri->dy31 - tri->dx31 * tri->dy12);
 323
 324    LP_COUNT(nr_tris);
 325
 326    /* Cull non-ccw and zero-sized triangles.
 327     *
 328     * XXX: subject to overflow??
 329     */
 330    if (area <= 0) {
 331       lp_scene_putback_data( scene, tri_bytes );
 332       LP_COUNT(nr_culled_tris);
 333       return;
 334    }
 335
 336    /* Bounding rectangle (in pixels) */
 337    minx = (MIN3(x1, x2, x3) + (FIXED_ONE-1)) >> FIXED_ORDER;
 338    maxx = (MAX3(x1, x2, x3) + (FIXED_ONE-1)) >> FIXED_ORDER;
 339    miny = (MIN3(y1, y2, y3) + (FIXED_ONE-1)) >> FIXED_ORDER;
 340    maxy = (MAX3(y1, y2, y3) + (FIXED_ONE-1)) >> FIXED_ORDER;
 341
 342    if (setup->scissor_test) {
 343       minx = MAX2(minx, setup->scissor.current.minx);
 344       maxx = MIN2(maxx, setup->scissor.current.maxx);
 345       miny = MAX2(miny, setup->scissor.current.miny);
 346       maxy = MIN2(maxy, setup->scissor.current.maxy);
 347    }
 348
 349    if (miny == maxy ||
 350        minx == maxx) {
 351       lp_scene_putback_data( scene, tri_bytes );
 352       LP_COUNT(nr_culled_tris);
 353       return;
 354    }
 355
 356    /*
 357     */
 358    oneoverarea = ((float)FIXED_ONE) / (float)area;
 359
 360    /* Setup parameter interpolants:
 361     */
 362    setup_tri_coefficients( setup, tri, oneoverarea, v1, v2, v3, frontfacing );
 363
 364    /* half-edge constants, will be interated over the whole render target.
 365     */
 366    tri->c1 = tri->dy12 * x1 - tri->dx12 * y1;
 367    tri->c2 = tri->dy23 * x2 - tri->dx23 * y2;
 368    tri->c3 = tri->dy31 * x3 - tri->dx31 * y3;
 369
 370    /* correct for top-left fill convention:
 371     */
 372    if (tri->dy12 < 0 || (tri->dy12 == 0 && tri->dx12 > 0)) tri->c1++;
 373    if (tri->dy23 < 0 || (tri->dy23 == 0 && tri->dx23 > 0)) tri->c2++;
 374    if (tri->dy31 < 0 || (tri->dy31 == 0 && tri->dx31 > 0)) tri->c3++;
 375
 376    tri->dy12 *= FIXED_ONE;
 377    tri->dy23 *= FIXED_ONE;
 378    tri->dy31 *= FIXED_ONE;
 379
 380    tri->dx12 *= FIXED_ONE;
 381    tri->dx23 *= FIXED_ONE;
 382    tri->dx31 *= FIXED_ONE;
 383
 384    /* find trivial reject offsets for each edge for a single-pixel
 385     * sized block.  These will be scaled up at each recursive level to
 386     * match the active blocksize.  Scaling in this way works best if
 387     * the blocks are square.
 388     */
 389    tri->eo1 = 0;
 390    if (tri->dy12 < 0) tri->eo1 -= tri->dy12;
 391    if (tri->dx12 > 0) tri->eo1 += tri->dx12;
 392
 393    tri->eo2 = 0;
 394    if (tri->dy23 < 0) tri->eo2 -= tri->dy23;
 395    if (tri->dx23 > 0) tri->eo2 += tri->dx23;
 396
 397    tri->eo3 = 0;
 398    if (tri->dy31 < 0) tri->eo3 -= tri->dy31;
 399    if (tri->dx31 > 0) tri->eo3 += tri->dx31;
 400
 401    /* Calculate trivial accept offsets from the above.
 402     */
 403    tri->ei1 = tri->dx12 - tri->dy12 - tri->eo1;
 404    tri->ei2 = tri->dx23 - tri->dy23 - tri->eo2;
 405    tri->ei3 = tri->dx31 - tri->dy31 - tri->eo3;
 406
 407    /* Fill in the inputs.step[][] arrays.
 408     * We've manually unrolled some loops here.
 409     */
 410    {
 411       const int xstep1 = -tri->dy12;
 412       const int xstep2 = -tri->dy23;
 413       const int xstep3 = -tri->dy31;
 414       const int ystep1 = tri->dx12;
 415       const int ystep2 = tri->dx23;
 416       const int ystep3 = tri->dx31;
 417
 418 #define SETUP_STEP(i, x, y)                                \
 419       do {                                                 \
 420          tri->inputs.step[0][i] = x * xstep1 + y * ystep1; \
 421          tri->inputs.step[1][i] = x * xstep2 + y * ystep2; \
 422          tri->inputs.step[2][i] = x * xstep3 + y * ystep3; \
 423       } while (0)
 424
 425       SETUP_STEP(0, 0, 0);
 426       SETUP_STEP(1, 1, 0);
 427       SETUP_STEP(2, 0, 1);
 428       SETUP_STEP(3, 1, 1);
 429
 430       SETUP_STEP(4, 2, 0);
 431       SETUP_STEP(5, 3, 0);
 432       SETUP_STEP(6, 2, 1);
 433       SETUP_STEP(7, 3, 1);
 434
 435       SETUP_STEP(8, 0, 2);
 436       SETUP_STEP(9, 1, 2);
 437       SETUP_STEP(10, 0, 3);
 438       SETUP_STEP(11, 1, 3);
 439
 440       SETUP_STEP(12, 2, 2);
 441       SETUP_STEP(13, 3, 2);
 442       SETUP_STEP(14, 2, 3);
 443       SETUP_STEP(15, 3, 3);
 444 #undef STEP
 445    }
 446
 447    /*
 448     * All fields of 'tri' are now set.  The remaining code here is
 449     * concerned with binning.
 450     */
 451
 452    /* Convert to tile coordinates:
 453     */
 454    minx = minx / TILE_SIZE;
 455    miny = miny / TILE_SIZE;
 456    maxx = maxx / TILE_SIZE;
 457    maxy = maxy / TILE_SIZE;
 458
 459    /*
 460     * Clamp to framebuffer size
 461     */
 462    minx = MAX2(minx, 0);
 463    miny = MAX2(miny, 0);
 464    maxx = MIN2(maxx, scene->tiles_x - 1);
 465    maxy = MIN2(maxy, scene->tiles_y - 1);
 466
 467    /* Determine which tile(s) intersect the triangle's bounding box
 468     */
 469    if (miny == maxy && minx == maxx)
 470    {
 471       /* Triangle is contained in a single tile:
 472        */
 473       lp_scene_bin_command( scene, minx, miny, lp_rast_triangle,
 474                             lp_rast_arg_triangle(tri) );
 475    }
 476    else
 477    {
 478       int c1 = (tri->c1 +
 479                 tri->dx12 * miny * TILE_SIZE -
 480                 tri->dy12 * minx * TILE_SIZE);
 481       int c2 = (tri->c2 +
 482                 tri->dx23 * miny * TILE_SIZE -
 483                 tri->dy23 * minx * TILE_SIZE);
 484       int c3 = (tri->c3 +
 485                 tri->dx31 * miny * TILE_SIZE -
 486                 tri->dy31 * minx * TILE_SIZE);
 487
 488       int ei1 = tri->ei1 << TILE_ORDER;
 489       int ei2 = tri->ei2 << TILE_ORDER;
 490       int ei3 = tri->ei3 << TILE_ORDER;
 491
 492       int eo1 = tri->eo1 << TILE_ORDER;
 493       int eo2 = tri->eo2 << TILE_ORDER;
 494       int eo3 = tri->eo3 << TILE_ORDER;
 495
 496       int xstep1 = -(tri->dy12 << TILE_ORDER);
 497       int xstep2 = -(tri->dy23 << TILE_ORDER);
 498       int xstep3 = -(tri->dy31 << TILE_ORDER);
 499
 500       int ystep1 = tri->dx12 << TILE_ORDER;
 501       int ystep2 = tri->dx23 << TILE_ORDER;
 502       int ystep3 = tri->dx31 << TILE_ORDER;
 503       int x, y;
 504
 505
 506       /* Test tile-sized blocks against the triangle.
 507        * Discard blocks fully outside the tri.  If the block is fully
 508        * contained inside the tri, bin an lp_rast_shade_tile command.
 509        * Else, bin a lp_rast_triangle command.
 510        */
 511       for (y = miny; y <= maxy; y++)
 512       {
 513          int cx1 = c1;
 514          int cx2 = c2;
 515          int cx3 = c3;
 516          boolean in = FALSE;  /* are we inside the triangle? */
 517
 518          for (x = minx; x <= maxx; x++)
 519          {
 520             if (cx1 + eo1 < 0 ||
 521                 cx2 + eo2 < 0 ||
 522                 cx3 + eo3 < 0)
 523             {
 524                /* do nothing */
 525                LP_COUNT(nr_empty_64);
 526                if (in)
 527                   break;  /* exiting triangle, all done with this row */
 528             }
 529             else if (cx1 + ei1 > 0 &&
 530                      cx2 + ei2 > 0 &&
 531                      cx3 + ei3 > 0)
 532             {
 533                /* triangle covers the whole tile- shade whole tile */
 534                LP_COUNT(nr_fully_covered_64);
 535                in = TRUE;
 536                if(setup->fs.current.opaque) {
 537                   lp_scene_bin_reset( scene, x, y );
 538                   lp_scene_bin_command( scene, x, y,
 539                                         lp_rast_set_state,
 540                                         lp_rast_arg_state(setup->fs.stored) );
 541                }
 542                lp_scene_bin_command( scene, x, y,
 543                                      lp_rast_shade_tile,
 544                                      lp_rast_arg_inputs(&tri->inputs) );
 545             }
 546             else
 547             {
 548                /* rasterizer/shade partial tile */
 549                LP_COUNT(nr_partially_covered_64);
 550                in = TRUE;
 551                lp_scene_bin_command( scene, x, y,
 552                                      lp_rast_triangle,
 553                                      lp_rast_arg_triangle(tri) );
 554             }
 555
 556             /* Iterate cx values across the region:
 557              */
 558             cx1 += xstep1;
 559             cx2 += xstep2;
 560             cx3 += xstep3;
 561          }
 562
 563          /* Iterate c values down the region:
 564           */
 565          c1 += ystep1;
 566          c2 += ystep2;
 567          c3 += ystep3;
 568       }
 569    }
 570 }
 571
 572
 573 static void triangle_cw( struct lp_setup_context *setup,
 574                          const float (*v0)[4],
 575                          const float (*v1)[4],
 576                          const float (*v2)[4] )
 577 {
 578    do_triangle_ccw( setup, v1, v0, v2, !setup->ccw_is_frontface );
 579 }
 580
 581
 582 static void triangle_ccw( struct lp_setup_context *setup,
 583                          const float (*v0)[4],
 584                          const float (*v1)[4],
 585                          const float (*v2)[4] )
 586 {
 587    do_triangle_ccw( setup, v0, v1, v2, setup->ccw_is_frontface );
 588 }
 589
 590
 591 static void triangle_both( struct lp_setup_context *setup,
 592                            const float (*v0)[4],
 593                            const float (*v1)[4],
 594                            const float (*v2)[4] )
 595 {
 596    /* edge vectors e = v0 - v2, f = v1 - v2 */
 597    const float ex = v0[0][0] - v2[0][0];
 598    const float ey = v0[0][1] - v2[0][1];
 599    const float fx = v1[0][0] - v2[0][0];
 600    const float fy = v1[0][1] - v2[0][1];
 601
 602    /* det = cross(e,f).z */
 603    if (ex * fy - ey * fx < 0.0f)
 604       triangle_ccw( setup, v0, v1, v2 );
 605    else
 606       triangle_cw( setup, v0, v1, v2 );
 607 }
 608
 609
 610 static void triangle_nop( struct lp_setup_context *setup,
 611                           const float (*v0)[4],
 612                           const float (*v1)[4],
 613                           const float (*v2)[4] )
 614 {
 615 }
 616
 617
 618 void
 619 lp_setup_choose_triangle( struct lp_setup_context *setup )
 620 {
 621    switch (setup->cullmode) {
 622    case PIPE_WINDING_NONE:
 623       setup->triangle = triangle_both;
 624       break;
 625    case PIPE_WINDING_CCW:
 626       setup->triangle = triangle_cw;
 627       break;
 628    case PIPE_WINDING_CW:
 629       setup->triangle = triangle_ccw;
 630       break;
 631    default:
 632       setup->triangle = triangle_nop;
 633       break;
 634    }
 635 }