src/mesa/main/stencil.c

   1 /*
   2  * Mesa 3-D graphics library
   3  *
   4  * Copyright (C) 1999-2007  Brian Paul   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 "Software"),
   8  * to deal in the Software without restriction, including without limitation
   9  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  10  * and/or sell copies of the Software, and to permit persons to whom the
  11  * Software is furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included
  14  * in all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  17  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  20  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  21  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  22  * OTHER DEALINGS IN THE SOFTWARE.
  23  */
  24
  25
  26 /**
  27  * \file stencil.c
  28  * Stencil operations.
  29  *
  30  * Note: There's some conflict between GL_EXT_stencil_two_side and
  31  * OpenGL 2.0's two-sided stencil feature.
  32  *
  33  * With GL_EXT_stencil_two_side, calling glStencilOp/Func/Mask() only the
  34  * front OR back face state (as set by glActiveStencilFaceEXT) is set.
  35  *
  36  * But with OpenGL 2.0, calling glStencilOp/Func/Mask() sets BOTH the
  37  * front AND back state.
  38  *
  39  * Also, note that GL_ATI_separate_stencil is different as well:
  40  * glStencilFuncSeparateATI(GLenum frontfunc, GLenum backfunc, ...)  vs.
  41  * glStencilFuncSeparate(GLenum face, GLenum func, ...).
  42  *
  43  * This problem is solved by keeping three sets of stencil state:
  44  *  state[0] = GL_FRONT state.
  45  *  state[1] = OpenGL 2.0 / GL_ATI_separate_stencil GL_BACK state.
  46  *  state[2] = GL_EXT_stencil_two_side GL_BACK state.
  47  */
  48
  49
  50 #include "glheader.h"
  51 #include "imports.h"
  52 #include "context.h"
  53 #include "macros.h"
  54 #include "stencil.h"
  55 #include "mtypes.h"
  56
  57
  58 static GLboolean
  59 validate_stencil_op(struct gl_context *ctx, GLenum op)
  60 {
  61    switch (op) {
  62    case GL_KEEP:
  63    case GL_ZERO:
  64    case GL_REPLACE:
  65    case GL_INCR:
  66    case GL_DECR:
  67    case GL_INVERT:
  68    case GL_INCR_WRAP:
  69    case GL_DECR_WRAP:
  70       return GL_TRUE;
  71    default:
  72       return GL_FALSE;
  73    }
  74 }
  75
  76
  77 static GLboolean
  78 validate_stencil_func(struct gl_context *ctx, GLenum func)
  79 {
  80    switch (func) {
  81    case GL_NEVER:
  82    case GL_LESS:
  83    case GL_LEQUAL:
  84    case GL_GREATER:
  85    case GL_GEQUAL:
  86    case GL_EQUAL:
  87    case GL_NOTEQUAL:
  88    case GL_ALWAYS:
  89       return GL_TRUE;
  90    default:
  91       return GL_FALSE;
  92    }
  93 }
  94
  95
  96 /**
  97  * Set the clear value for the stencil buffer.
  98  *
  99  * \param s clear value.
 100  *
 101  * \sa glClearStencil().
 102  *
 103  * Updates gl_stencil_attrib::Clear. On change
 104  * flushes the vertices and notifies the driver via
 105  * the dd_function_table::ClearStencil callback.
 106  */
 107 void GLAPIENTRY
 108 _mesa_ClearStencil( GLint s )
 109 {
 110    GET_CURRENT_CONTEXT(ctx);
 111
 112    if (MESA_VERBOSE & VERBOSE_API)
 113       _mesa_debug(ctx, "glClearStencil(%d)\n", s);
 114
 115    ctx->Stencil.Clear = (GLuint) s;
 116 }
 117
 118
 119 /**
 120  * Set the function and reference value for stencil testing.
 121  *
 122  * \param frontfunc front test function.
 123  * \param backfunc back test function.
 124  * \param ref front and back reference value.
 125  * \param mask front and back bitmask.
 126  *
 127  * \sa glStencilFunc().
 128  *
 129  * Verifies the parameters and updates the respective values in
 130  * __struct gl_contextRec::Stencil. On change flushes the vertices and notifies
 131  * the driver via the dd_function_table::StencilFunc callback.
 132  */
 133 void GLAPIENTRY
 134 _mesa_StencilFuncSeparateATI( GLenum frontfunc, GLenum backfunc, GLint ref, GLuint mask )
 135 {
 136    GET_CURRENT_CONTEXT(ctx);
 137
 138    if (MESA_VERBOSE & VERBOSE_API)
 139       _mesa_debug(ctx, "glStencilFuncSeparateATI()\n");
 140
 141    if (!validate_stencil_func(ctx, frontfunc)) {
 142       _mesa_error(ctx, GL_INVALID_ENUM,
 143                   "glStencilFuncSeparateATI(frontfunc)");
 144       return;
 145    }
 146    if (!validate_stencil_func(ctx, backfunc)) {
 147       _mesa_error(ctx, GL_INVALID_ENUM,
 148                   "glStencilFuncSeparateATI(backfunc)");
 149       return;
 150    }
 151
 152    /* set both front and back state */
 153    if (ctx->Stencil.Function[0] == frontfunc &&
 154        ctx->Stencil.Function[1] == backfunc &&
 155        ctx->Stencil.ValueMask[0] == mask &&
 156        ctx->Stencil.ValueMask[1] == mask &&
 157        ctx->Stencil.Ref[0] == ref &&
 158        ctx->Stencil.Ref[1] == ref)
 159       return;
 160    FLUSH_VERTICES(ctx, _NEW_STENCIL);
 161    ctx->Stencil.Function[0]  = frontfunc;
 162    ctx->Stencil.Function[1]  = backfunc;
 163    ctx->Stencil.Ref[0]       = ctx->Stencil.Ref[1]       = ref;
 164    ctx->Stencil.ValueMask[0] = ctx->Stencil.ValueMask[1] = mask;
 165    if (ctx->Driver.StencilFuncSeparate) {
 166       ctx->Driver.StencilFuncSeparate(ctx, GL_FRONT,
 167                                       frontfunc, ref, mask);
 168       ctx->Driver.StencilFuncSeparate(ctx, GL_BACK,
 169                                       backfunc, ref, mask);
 170    }
 171 }
 172
 173
 174 /**
 175  * Set the function and reference value for stencil testing.
 176  *
 177  * \param func test function.
 178  * \param ref reference value.
 179  * \param mask bitmask.
 180  *
 181  * \sa glStencilFunc().
 182  *
 183  * Verifies the parameters and updates the respective values in
 184  * __struct gl_contextRec::Stencil. On change flushes the vertices and notifies
 185  * the driver via the dd_function_table::StencilFunc callback.
 186  */
 187 void GLAPIENTRY
 188 _mesa_StencilFunc( GLenum func, GLint ref, GLuint mask )
 189 {
 190    GET_CURRENT_CONTEXT(ctx);
 191    const GLint face = ctx->Stencil.ActiveFace;
 192
 193    if (MESA_VERBOSE & VERBOSE_API)
 194       _mesa_debug(ctx, "glStencilFunc()\n");
 195
 196    if (!validate_stencil_func(ctx, func)) {
 197       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilFunc(func)");
 198       return;
 199    }
 200
 201    if (face != 0) {
 202       if (ctx->Stencil.Function[face] == func &&
 203           ctx->Stencil.ValueMask[face] == mask &&
 204           ctx->Stencil.Ref[face] == ref)
 205          return;
 206       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 207       ctx->Stencil.Function[face] = func;
 208       ctx->Stencil.Ref[face] = ref;
 209       ctx->Stencil.ValueMask[face] = mask;
 210
 211       /* Only propagate the change to the driver if EXT_stencil_two_side
 212        * is enabled.
 213        */
 214       if (ctx->Driver.StencilFuncSeparate && ctx->Stencil.TestTwoSide) {
 215          ctx->Driver.StencilFuncSeparate(ctx, GL_BACK, func, ref, mask);
 216       }
 217    }
 218    else {
 219       /* set both front and back state */
 220       if (ctx->Stencil.Function[0] == func &&
 221           ctx->Stencil.Function[1] == func &&
 222           ctx->Stencil.ValueMask[0] == mask &&
 223           ctx->Stencil.ValueMask[1] == mask &&
 224           ctx->Stencil.Ref[0] == ref &&
 225           ctx->Stencil.Ref[1] == ref)
 226          return;
 227       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 228       ctx->Stencil.Function[0]  = ctx->Stencil.Function[1]  = func;
 229       ctx->Stencil.Ref[0]       = ctx->Stencil.Ref[1]       = ref;
 230       ctx->Stencil.ValueMask[0] = ctx->Stencil.ValueMask[1] = mask;
 231       if (ctx->Driver.StencilFuncSeparate) {
 232          ctx->Driver.StencilFuncSeparate(ctx,
 233                                          ((ctx->Stencil.TestTwoSide)
 234                                           ? GL_FRONT : GL_FRONT_AND_BACK),
 235                                          func, ref, mask);
 236       }
 237    }
 238 }
 239
 240
 241 /**
 242  * Set the stencil writing mask.
 243  *
 244  * \param mask bit-mask to enable/disable writing of individual bits in the
 245  * stencil planes.
 246  *
 247  * \sa glStencilMask().
 248  *
 249  * Updates gl_stencil_attrib::WriteMask. On change flushes the vertices and
 250  * notifies the driver via the dd_function_table::StencilMask callback.
 251  */
 252 void GLAPIENTRY
 253 _mesa_StencilMask( GLuint mask )
 254 {
 255    GET_CURRENT_CONTEXT(ctx);
 256    const GLint face = ctx->Stencil.ActiveFace;
 257
 258    if (MESA_VERBOSE & VERBOSE_API)
 259       _mesa_debug(ctx, "glStencilMask()\n");
 260
 261    if (face != 0) {
 262       /* Only modify the EXT_stencil_two_side back-face state.
 263        */
 264       if (ctx->Stencil.WriteMask[face] == mask)
 265          return;
 266       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 267       ctx->Stencil.WriteMask[face] = mask;
 268
 269       /* Only propagate the change to the driver if EXT_stencil_two_side
 270        * is enabled.
 271        */
 272       if (ctx->Driver.StencilMaskSeparate && ctx->Stencil.TestTwoSide) {
 273          ctx->Driver.StencilMaskSeparate(ctx, GL_BACK, mask);
 274       }
 275    }
 276    else {
 277       /* set both front and back state */
 278       if (ctx->Stencil.WriteMask[0] == mask &&
 279           ctx->Stencil.WriteMask[1] == mask)
 280          return;
 281       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 282       ctx->Stencil.WriteMask[0] = ctx->Stencil.WriteMask[1] = mask;
 283       if (ctx->Driver.StencilMaskSeparate) {
 284          ctx->Driver.StencilMaskSeparate(ctx,
 285                                          ((ctx->Stencil.TestTwoSide)
 286                                           ? GL_FRONT : GL_FRONT_AND_BACK),
 287                                           mask);
 288       }
 289    }
 290 }
 291
 292
 293 /**
 294  * Set the stencil test actions.
 295  *
 296  * \param fail action to take when stencil test fails.
 297  * \param zfail action to take when stencil test passes, but depth test fails.
 298  * \param zpass action to take when stencil test passes and the depth test
 299  * passes (or depth testing is not enabled).
 300  *
 301  * \sa glStencilOp().
 302  *
 303  * Verifies the parameters and updates the respective fields in
 304  * __struct gl_contextRec::Stencil. On change flushes the vertices and notifies
 305  * the driver via the dd_function_table::StencilOp callback.
 306  */
 307 void GLAPIENTRY
 308 _mesa_StencilOp(GLenum fail, GLenum zfail, GLenum zpass)
 309 {
 310    GET_CURRENT_CONTEXT(ctx);
 311    const GLint face = ctx->Stencil.ActiveFace;
 312
 313    if (MESA_VERBOSE & VERBOSE_API)
 314       _mesa_debug(ctx, "glStencilOp()\n");
 315
 316    if (!validate_stencil_op(ctx, fail)) {
 317       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOp(sfail)");
 318       return;
 319    }
 320    if (!validate_stencil_op(ctx, zfail)) {
 321       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOp(zfail)");
 322       return;
 323    }
 324    if (!validate_stencil_op(ctx, zpass)) {
 325       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOp(zpass)");
 326       return;
 327    }
 328
 329    if (face != 0) {
 330       /* only set active face state */
 331       if (ctx->Stencil.ZFailFunc[face] == zfail &&
 332           ctx->Stencil.ZPassFunc[face] == zpass &&
 333           ctx->Stencil.FailFunc[face] == fail)
 334          return;
 335       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 336       ctx->Stencil.ZFailFunc[face] = zfail;
 337       ctx->Stencil.ZPassFunc[face] = zpass;
 338       ctx->Stencil.FailFunc[face] = fail;
 339
 340       /* Only propagate the change to the driver if EXT_stencil_two_side
 341        * is enabled.
 342        */
 343       if (ctx->Driver.StencilOpSeparate && ctx->Stencil.TestTwoSide) {
 344          ctx->Driver.StencilOpSeparate(ctx, GL_BACK, fail, zfail, zpass);
 345       }
 346    }
 347    else {
 348       /* set both front and back state */
 349       if (ctx->Stencil.ZFailFunc[0] == zfail &&
 350           ctx->Stencil.ZFailFunc[1] == zfail &&
 351           ctx->Stencil.ZPassFunc[0] == zpass &&
 352           ctx->Stencil.ZPassFunc[1] == zpass &&
 353           ctx->Stencil.FailFunc[0] == fail &&
 354           ctx->Stencil.FailFunc[1] == fail)
 355          return;
 356       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 357       ctx->Stencil.ZFailFunc[0] = ctx->Stencil.ZFailFunc[1] = zfail;
 358       ctx->Stencil.ZPassFunc[0] = ctx->Stencil.ZPassFunc[1] = zpass;
 359       ctx->Stencil.FailFunc[0]  = ctx->Stencil.FailFunc[1]  = fail;
 360       if (ctx->Driver.StencilOpSeparate) {
 361          ctx->Driver.StencilOpSeparate(ctx,
 362                                        ((ctx->Stencil.TestTwoSide)
 363                                         ? GL_FRONT : GL_FRONT_AND_BACK),
 364                                        fail, zfail, zpass);
 365       }
 366    }
 367 }
 368
 369
 370
 371 /* GL_EXT_stencil_two_side */
 372 void GLAPIENTRY
 373 _mesa_ActiveStencilFaceEXT(GLenum face)
 374 {
 375    GET_CURRENT_CONTEXT(ctx);
 376
 377    if (MESA_VERBOSE & VERBOSE_API)
 378       _mesa_debug(ctx, "glActiveStencilFaceEXT()\n");
 379
 380    if (!ctx->Extensions.EXT_stencil_two_side) {
 381       _mesa_error(ctx, GL_INVALID_OPERATION, "glActiveStencilFaceEXT");
 382       return;
 383    }
 384
 385    if (face == GL_FRONT || face == GL_BACK) {
 386       ctx->Stencil.ActiveFace = (face == GL_FRONT) ? 0 : 2;
 387    }
 388    else {
 389       _mesa_error(ctx, GL_INVALID_ENUM, "glActiveStencilFaceEXT(face)");
 390    }
 391 }
 392
 393
 394
 395 void GLAPIENTRY
 396 _mesa_StencilOpSeparate(GLenum face, GLenum sfail, GLenum zfail, GLenum zpass)
 397 {
 398    GLboolean set = GL_FALSE;
 399    GET_CURRENT_CONTEXT(ctx);
 400
 401    if (MESA_VERBOSE & VERBOSE_API)
 402       _mesa_debug(ctx, "glStencilOpSeparate()\n");
 403
 404    if (!validate_stencil_op(ctx, sfail)) {
 405       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(sfail)");
 406       return;
 407    }
 408    if (!validate_stencil_op(ctx, zfail)) {
 409       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(zfail)");
 410       return;
 411    }
 412    if (!validate_stencil_op(ctx, zpass)) {
 413       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(zpass)");
 414       return;
 415    }
 416    if (face != GL_FRONT && face != GL_BACK && face != GL_FRONT_AND_BACK) {
 417       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(face)");
 418       return;
 419    }
 420
 421    if (face != GL_BACK) {
 422       /* set front */
 423       if (ctx->Stencil.ZFailFunc[0] != zfail ||
 424           ctx->Stencil.ZPassFunc[0] != zpass ||
 425           ctx->Stencil.FailFunc[0] != sfail){
 426          FLUSH_VERTICES(ctx, _NEW_STENCIL);
 427          ctx->Stencil.ZFailFunc[0] = zfail;
 428          ctx->Stencil.ZPassFunc[0] = zpass;
 429          ctx->Stencil.FailFunc[0] = sfail;
 430          set = GL_TRUE;
 431       }
 432    }
 433    if (face != GL_FRONT) {
 434       /* set back */
 435       if (ctx->Stencil.ZFailFunc[1] != zfail ||
 436           ctx->Stencil.ZPassFunc[1] != zpass ||
 437           ctx->Stencil.FailFunc[1] != sfail) {
 438          FLUSH_VERTICES(ctx, _NEW_STENCIL);
 439          ctx->Stencil.ZFailFunc[1] = zfail;
 440          ctx->Stencil.ZPassFunc[1] = zpass;
 441          ctx->Stencil.FailFunc[1] = sfail;
 442          set = GL_TRUE;
 443       }
 444    }
 445    if (set && ctx->Driver.StencilOpSeparate) {
 446       ctx->Driver.StencilOpSeparate(ctx, face, sfail, zfail, zpass);
 447    }
 448 }
 449
 450
 451 static void
 452 stencil_func_separate(struct gl_context *ctx, GLenum face, GLenum func,
 453                       GLint ref, GLuint mask)
 454 {
 455    FLUSH_VERTICES(ctx, _NEW_STENCIL);
 456
 457    if (face != GL_BACK) {
 458       /* set front */
 459       ctx->Stencil.Function[0] = func;
 460       ctx->Stencil.Ref[0] = ref;
 461       ctx->Stencil.ValueMask[0] = mask;
 462    }
 463
 464    if (face != GL_FRONT) {
 465       /* set back */
 466       ctx->Stencil.Function[1] = func;
 467       ctx->Stencil.Ref[1] = ref;
 468       ctx->Stencil.ValueMask[1] = mask;
 469    }
 470
 471    if (ctx->Driver.StencilFuncSeparate) {
 472       ctx->Driver.StencilFuncSeparate(ctx, face, func, ref, mask);
 473    }
 474 }
 475
 476
 477 /* OpenGL 2.0 */
 478 void GLAPIENTRY
 479 _mesa_StencilFuncSeparate_no_error(GLenum face, GLenum func, GLint ref,
 480                                    GLuint mask)
 481 {
 482    GET_CURRENT_CONTEXT(ctx);
 483    stencil_func_separate(ctx, face, func, ref, mask);
 484 }
 485
 486
 487 void GLAPIENTRY
 488 _mesa_StencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask)
 489 {
 490    GET_CURRENT_CONTEXT(ctx);
 491
 492    if (MESA_VERBOSE & VERBOSE_API)
 493       _mesa_debug(ctx, "glStencilFuncSeparate()\n");
 494
 495    if (face != GL_FRONT && face != GL_BACK && face != GL_FRONT_AND_BACK) {
 496       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilFuncSeparate(face)");
 497       return;
 498    }
 499
 500    if (!validate_stencil_func(ctx, func)) {
 501       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilFuncSeparate(func)");
 502       return;
 503    }
 504
 505    stencil_func_separate(ctx, face, func, ref, mask);
 506 }
 507
 508
 509 /* OpenGL 2.0 */
 510 void GLAPIENTRY
 511 _mesa_StencilMaskSeparate(GLenum face, GLuint mask)
 512 {
 513    GET_CURRENT_CONTEXT(ctx);
 514
 515    if (MESA_VERBOSE & VERBOSE_API)
 516       _mesa_debug(ctx, "glStencilMaskSeparate()\n");
 517
 518    if (face != GL_FRONT && face != GL_BACK && face != GL_FRONT_AND_BACK) {
 519       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilaMaskSeparate(face)");
 520       return;
 521    }
 522
 523    FLUSH_VERTICES(ctx, _NEW_STENCIL);
 524
 525    if (face != GL_BACK) {
 526       ctx->Stencil.WriteMask[0] = mask;
 527    }
 528    if (face != GL_FRONT) {
 529       ctx->Stencil.WriteMask[1] = mask;
 530    }
 531    if (ctx->Driver.StencilMaskSeparate) {
 532       ctx->Driver.StencilMaskSeparate(ctx, face, mask);
 533    }
 534 }
 535
 536
 537 /**
 538  * Update derived stencil state.
 539  */
 540 void
 541 _mesa_update_stencil(struct gl_context *ctx)
 542 {
 543    const GLint face = ctx->Stencil._BackFace;
 544
 545    ctx->Stencil._Enabled = (ctx->Stencil.Enabled &&
 546                             ctx->DrawBuffer->Visual.stencilBits > 0);
 547
 548     ctx->Stencil._TestTwoSide =
 549        ctx->Stencil._Enabled &&
 550        (ctx->Stencil.Function[0] != ctx->Stencil.Function[face] ||
 551         ctx->Stencil.FailFunc[0] != ctx->Stencil.FailFunc[face] ||
 552         ctx->Stencil.ZPassFunc[0] != ctx->Stencil.ZPassFunc[face] ||
 553         ctx->Stencil.ZFailFunc[0] != ctx->Stencil.ZFailFunc[face] ||
 554         ctx->Stencil.Ref[0] != ctx->Stencil.Ref[face] ||
 555         ctx->Stencil.ValueMask[0] != ctx->Stencil.ValueMask[face] ||
 556         ctx->Stencil.WriteMask[0] != ctx->Stencil.WriteMask[face]);
 557
 558    ctx->Stencil._WriteEnabled =
 559       ctx->Stencil._Enabled &&
 560       (ctx->Stencil.WriteMask[0] != 0 ||
 561        (ctx->Stencil._TestTwoSide && ctx->Stencil.WriteMask[face] != 0));
 562 }
 563
 564
 565 /**
 566  * Initialize the context stipple state.
 567  *
 568  * \param ctx GL context.
 569  *
 570  * Initializes __struct gl_contextRec::Stencil attribute group.
 571  */
 572 void
 573 _mesa_init_stencil(struct gl_context *ctx)
 574 {
 575    ctx->Stencil.Enabled = GL_FALSE;
 576    ctx->Stencil.TestTwoSide = GL_FALSE;
 577    ctx->Stencil.ActiveFace = 0;  /* 0 = GL_FRONT, 2 = GL_BACK */
 578    ctx->Stencil.Function[0] = GL_ALWAYS;
 579    ctx->Stencil.Function[1] = GL_ALWAYS;
 580    ctx->Stencil.Function[2] = GL_ALWAYS;
 581    ctx->Stencil.FailFunc[0] = GL_KEEP;
 582    ctx->Stencil.FailFunc[1] = GL_KEEP;
 583    ctx->Stencil.FailFunc[2] = GL_KEEP;
 584    ctx->Stencil.ZPassFunc[0] = GL_KEEP;
 585    ctx->Stencil.ZPassFunc[1] = GL_KEEP;
 586    ctx->Stencil.ZPassFunc[2] = GL_KEEP;
 587    ctx->Stencil.ZFailFunc[0] = GL_KEEP;
 588    ctx->Stencil.ZFailFunc[1] = GL_KEEP;
 589    ctx->Stencil.ZFailFunc[2] = GL_KEEP;
 590    ctx->Stencil.Ref[0] = 0;
 591    ctx->Stencil.Ref[1] = 0;
 592    ctx->Stencil.Ref[2] = 0;
 593
 594    /* 4.1.4 Stencil Test section of the GL-ES 3.0 specification says:
 595     *
 596     *     "In the initial state, [...] the front and back stencil mask are both
 597     *     set to the value 2^s − 1, where s is greater than or equal to the
 598     *     number of bits in the deepest stencil buffer* supported by the GL
 599     *     implementation."
 600     *
 601     * Since the maximum supported precision for stencil buffers is 8 bits,
 602     * mask values should be initialized to 2^8 - 1 = 0xFF.
 603     */
 604    ctx->Stencil.ValueMask[0] = 0xFF;
 605    ctx->Stencil.ValueMask[1] = 0xFF;
 606    ctx->Stencil.ValueMask[2] = 0xFF;
 607    ctx->Stencil.WriteMask[0] = 0xFF;
 608    ctx->Stencil.WriteMask[1] = 0xFF;
 609    ctx->Stencil.WriteMask[2] = 0xFF;
 610
 611    ctx->Stencil.Clear = 0;
 612    ctx->Stencil._BackFace = 1;
 613 }