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    ctx->Stencil.Clear = (GLuint) s;
 113 }
 114
 115
 116 /**
 117  * Set the function and reference value for stencil testing.
 118  *
 119  * \param frontfunc front test function.
 120  * \param backfunc back test function.
 121  * \param ref front and back reference value.
 122  * \param mask front and back bitmask.
 123  *
 124  * \sa glStencilFunc().
 125  *
 126  * Verifies the parameters and updates the respective values in
 127  * __struct gl_contextRec::Stencil. On change flushes the vertices and notifies the
 128  * driver via the dd_function_table::StencilFunc callback.
 129  */
 130 void GLAPIENTRY
 131 _mesa_StencilFuncSeparateATI( GLenum frontfunc, GLenum backfunc, GLint ref, GLuint mask )
 132 {
 133    GET_CURRENT_CONTEXT(ctx);
 134
 135    if (MESA_VERBOSE & VERBOSE_API)
 136       _mesa_debug(ctx, "glStencilFuncSeparateATI()\n");
 137
 138    if (!validate_stencil_func(ctx, frontfunc)) {
 139       _mesa_error(ctx, GL_INVALID_ENUM,
 140                   "glStencilFuncSeparateATI(frontfunc)");
 141       return;
 142    }
 143    if (!validate_stencil_func(ctx, backfunc)) {
 144       _mesa_error(ctx, GL_INVALID_ENUM,
 145                   "glStencilFuncSeparateATI(backfunc)");
 146       return;
 147    }
 148
 149    /* set both front and back state */
 150    if (ctx->Stencil.Function[0] == frontfunc &&
 151        ctx->Stencil.Function[1] == backfunc &&
 152        ctx->Stencil.ValueMask[0] == mask &&
 153        ctx->Stencil.ValueMask[1] == mask &&
 154        ctx->Stencil.Ref[0] == ref &&
 155        ctx->Stencil.Ref[1] == ref)
 156       return;
 157    FLUSH_VERTICES(ctx, _NEW_STENCIL);
 158    ctx->Stencil.Function[0]  = frontfunc;
 159    ctx->Stencil.Function[1]  = backfunc;
 160    ctx->Stencil.Ref[0]       = ctx->Stencil.Ref[1]       = ref;
 161    ctx->Stencil.ValueMask[0] = ctx->Stencil.ValueMask[1] = mask;
 162    if (ctx->Driver.StencilFuncSeparate) {
 163       ctx->Driver.StencilFuncSeparate(ctx, GL_FRONT,
 164                                       frontfunc, ref, mask);
 165       ctx->Driver.StencilFuncSeparate(ctx, GL_BACK,
 166                                       backfunc, ref, mask);
 167    }
 168 }
 169
 170
 171 /**
 172  * Set the function and reference value for stencil testing.
 173  *
 174  * \param func test function.
 175  * \param ref reference value.
 176  * \param mask bitmask.
 177  *
 178  * \sa glStencilFunc().
 179  *
 180  * Verifies the parameters and updates the respective values in
 181  * __struct gl_contextRec::Stencil. On change flushes the vertices and notifies the
 182  * driver via the dd_function_table::StencilFunc callback.
 183  */
 184 void GLAPIENTRY
 185 _mesa_StencilFunc( GLenum func, GLint ref, GLuint mask )
 186 {
 187    GET_CURRENT_CONTEXT(ctx);
 188    const GLint face = ctx->Stencil.ActiveFace;
 189
 190    if (MESA_VERBOSE & VERBOSE_API)
 191       _mesa_debug(ctx, "glStencilFunc()\n");
 192
 193    if (!validate_stencil_func(ctx, func)) {
 194       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilFunc(func)");
 195       return;
 196    }
 197
 198    if (face != 0) {
 199       if (ctx->Stencil.Function[face] == func &&
 200           ctx->Stencil.ValueMask[face] == mask &&
 201           ctx->Stencil.Ref[face] == ref)
 202          return;
 203       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 204       ctx->Stencil.Function[face] = func;
 205       ctx->Stencil.Ref[face] = ref;
 206       ctx->Stencil.ValueMask[face] = mask;
 207
 208       /* Only propagate the change to the driver if EXT_stencil_two_side
 209        * is enabled.
 210        */
 211       if (ctx->Driver.StencilFuncSeparate && ctx->Stencil.TestTwoSide) {
 212          ctx->Driver.StencilFuncSeparate(ctx, GL_BACK, func, ref, mask);
 213       }
 214    }
 215    else {
 216       /* set both front and back state */
 217       if (ctx->Stencil.Function[0] == func &&
 218           ctx->Stencil.Function[1] == func &&
 219           ctx->Stencil.ValueMask[0] == mask &&
 220           ctx->Stencil.ValueMask[1] == mask &&
 221           ctx->Stencil.Ref[0] == ref &&
 222           ctx->Stencil.Ref[1] == ref)
 223          return;
 224       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 225       ctx->Stencil.Function[0]  = ctx->Stencil.Function[1]  = func;
 226       ctx->Stencil.Ref[0]       = ctx->Stencil.Ref[1]       = ref;
 227       ctx->Stencil.ValueMask[0] = ctx->Stencil.ValueMask[1] = mask;
 228       if (ctx->Driver.StencilFuncSeparate) {
 229          ctx->Driver.StencilFuncSeparate(ctx,
 230                                          ((ctx->Stencil.TestTwoSide)
 231                                           ? GL_FRONT : GL_FRONT_AND_BACK),
 232                                          func, ref, mask);
 233       }
 234    }
 235 }
 236
 237
 238 /**
 239  * Set the stencil writing mask.
 240  *
 241  * \param mask bit-mask to enable/disable writing of individual bits in the
 242  * stencil planes.
 243  *
 244  * \sa glStencilMask().
 245  *
 246  * Updates gl_stencil_attrib::WriteMask. On change flushes the vertices and
 247  * notifies the driver via the dd_function_table::StencilMask callback.
 248  */
 249 void GLAPIENTRY
 250 _mesa_StencilMask( GLuint mask )
 251 {
 252    GET_CURRENT_CONTEXT(ctx);
 253    const GLint face = ctx->Stencil.ActiveFace;
 254
 255    if (MESA_VERBOSE & VERBOSE_API)
 256       _mesa_debug(ctx, "glStencilMask()\n");
 257
 258    if (face != 0) {
 259       /* Only modify the EXT_stencil_two_side back-face state.
 260        */
 261       if (ctx->Stencil.WriteMask[face] == mask)
 262          return;
 263       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 264       ctx->Stencil.WriteMask[face] = mask;
 265
 266       /* Only propagate the change to the driver if EXT_stencil_two_side
 267        * is enabled.
 268        */
 269       if (ctx->Driver.StencilMaskSeparate && ctx->Stencil.TestTwoSide) {
 270          ctx->Driver.StencilMaskSeparate(ctx, GL_BACK, mask);
 271       }
 272    }
 273    else {
 274       /* set both front and back state */
 275       if (ctx->Stencil.WriteMask[0] == mask &&
 276           ctx->Stencil.WriteMask[1] == mask)
 277          return;
 278       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 279       ctx->Stencil.WriteMask[0] = ctx->Stencil.WriteMask[1] = mask;
 280       if (ctx->Driver.StencilMaskSeparate) {
 281          ctx->Driver.StencilMaskSeparate(ctx,
 282                                          ((ctx->Stencil.TestTwoSide)
 283                                           ? GL_FRONT : GL_FRONT_AND_BACK),
 284                                           mask);
 285       }
 286    }
 287 }
 288
 289
 290 /**
 291  * Set the stencil test actions.
 292  *
 293  * \param fail action to take when stencil test fails.
 294  * \param zfail action to take when stencil test passes, but depth test fails.
 295  * \param zpass action to take when stencil test passes and the depth test
 296  * passes (or depth testing is not enabled).
 297  *
 298  * \sa glStencilOp().
 299  *
 300  * Verifies the parameters and updates the respective fields in
 301  * __struct gl_contextRec::Stencil. On change flushes the vertices and notifies the
 302  * driver via the dd_function_table::StencilOp callback.
 303  */
 304 void GLAPIENTRY
 305 _mesa_StencilOp(GLenum fail, GLenum zfail, GLenum zpass)
 306 {
 307    GET_CURRENT_CONTEXT(ctx);
 308    const GLint face = ctx->Stencil.ActiveFace;
 309
 310    if (MESA_VERBOSE & VERBOSE_API)
 311       _mesa_debug(ctx, "glStencilOp()\n");
 312
 313    if (!validate_stencil_op(ctx, fail)) {
 314       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOp(sfail)");
 315       return;
 316    }
 317    if (!validate_stencil_op(ctx, zfail)) {
 318       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOp(zfail)");
 319       return;
 320    }
 321    if (!validate_stencil_op(ctx, zpass)) {
 322       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOp(zpass)");
 323       return;
 324    }
 325
 326    if (face != 0) {
 327       /* only set active face state */
 328       if (ctx->Stencil.ZFailFunc[face] == zfail &&
 329           ctx->Stencil.ZPassFunc[face] == zpass &&
 330           ctx->Stencil.FailFunc[face] == fail)
 331          return;
 332       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 333       ctx->Stencil.ZFailFunc[face] = zfail;
 334       ctx->Stencil.ZPassFunc[face] = zpass;
 335       ctx->Stencil.FailFunc[face] = fail;
 336
 337       /* Only propagate the change to the driver if EXT_stencil_two_side
 338        * is enabled.
 339        */
 340       if (ctx->Driver.StencilOpSeparate && ctx->Stencil.TestTwoSide) {
 341          ctx->Driver.StencilOpSeparate(ctx, GL_BACK, fail, zfail, zpass);
 342       }
 343    }
 344    else {
 345       /* set both front and back state */
 346       if (ctx->Stencil.ZFailFunc[0] == zfail &&
 347           ctx->Stencil.ZFailFunc[1] == zfail &&
 348           ctx->Stencil.ZPassFunc[0] == zpass &&
 349           ctx->Stencil.ZPassFunc[1] == zpass &&
 350           ctx->Stencil.FailFunc[0] == fail &&
 351           ctx->Stencil.FailFunc[1] == fail)
 352          return;
 353       FLUSH_VERTICES(ctx, _NEW_STENCIL);
 354       ctx->Stencil.ZFailFunc[0] = ctx->Stencil.ZFailFunc[1] = zfail;
 355       ctx->Stencil.ZPassFunc[0] = ctx->Stencil.ZPassFunc[1] = zpass;
 356       ctx->Stencil.FailFunc[0]  = ctx->Stencil.FailFunc[1]  = fail;
 357       if (ctx->Driver.StencilOpSeparate) {
 358          ctx->Driver.StencilOpSeparate(ctx,
 359                                        ((ctx->Stencil.TestTwoSide)
 360                                         ? GL_FRONT : GL_FRONT_AND_BACK),
 361                                        fail, zfail, zpass);
 362       }
 363    }
 364 }
 365
 366
 367
 368 /* GL_EXT_stencil_two_side */
 369 void GLAPIENTRY
 370 _mesa_ActiveStencilFaceEXT(GLenum face)
 371 {
 372    GET_CURRENT_CONTEXT(ctx);
 373
 374    if (MESA_VERBOSE & VERBOSE_API)
 375       _mesa_debug(ctx, "glActiveStencilFaceEXT()\n");
 376
 377    if (!ctx->Extensions.EXT_stencil_two_side) {
 378       _mesa_error(ctx, GL_INVALID_OPERATION, "glActiveStencilFaceEXT");
 379       return;
 380    }
 381
 382    if (face == GL_FRONT || face == GL_BACK) {
 383       ctx->Stencil.ActiveFace = (face == GL_FRONT) ? 0 : 2;
 384    }
 385    else {
 386       _mesa_error(ctx, GL_INVALID_ENUM, "glActiveStencilFaceEXT(face)");
 387    }
 388 }
 389
 390
 391
 392 /**
 393  * OpenGL 2.0 function.
 394  * \todo Make StencilOp() call this function.  And eventually remove the
 395  * ctx->Driver.StencilOp function and use ctx->Driver.StencilOpSeparate
 396  * instead.
 397  */
 398 void GLAPIENTRY
 399 _mesa_StencilOpSeparate(GLenum face, GLenum sfail, GLenum zfail, GLenum zpass)
 400 {
 401    GLboolean set = GL_FALSE;
 402    GET_CURRENT_CONTEXT(ctx);
 403
 404    if (MESA_VERBOSE & VERBOSE_API)
 405       _mesa_debug(ctx, "glStencilOpSeparate()\n");
 406
 407    if (!validate_stencil_op(ctx, sfail)) {
 408       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(sfail)");
 409       return;
 410    }
 411    if (!validate_stencil_op(ctx, zfail)) {
 412       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(zfail)");
 413       return;
 414    }
 415    if (!validate_stencil_op(ctx, zpass)) {
 416       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(zpass)");
 417       return;
 418    }
 419    if (face != GL_FRONT && face != GL_BACK && face != GL_FRONT_AND_BACK) {
 420       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilOpSeparate(face)");
 421       return;
 422    }
 423
 424    if (face != GL_BACK) {
 425       /* set front */
 426       if (ctx->Stencil.ZFailFunc[0] != zfail ||
 427           ctx->Stencil.ZPassFunc[0] != zpass ||
 428           ctx->Stencil.FailFunc[0] != sfail){
 429          FLUSH_VERTICES(ctx, _NEW_STENCIL);
 430          ctx->Stencil.ZFailFunc[0] = zfail;
 431          ctx->Stencil.ZPassFunc[0] = zpass;
 432          ctx->Stencil.FailFunc[0] = sfail;
 433          set = GL_TRUE;
 434       }
 435    }
 436    if (face != GL_FRONT) {
 437       /* set back */
 438       if (ctx->Stencil.ZFailFunc[1] != zfail ||
 439           ctx->Stencil.ZPassFunc[1] != zpass ||
 440           ctx->Stencil.FailFunc[1] != sfail) {
 441          FLUSH_VERTICES(ctx, _NEW_STENCIL);
 442          ctx->Stencil.ZFailFunc[1] = zfail;
 443          ctx->Stencil.ZPassFunc[1] = zpass;
 444          ctx->Stencil.FailFunc[1] = sfail;
 445          set = GL_TRUE;
 446       }
 447    }
 448    if (set && ctx->Driver.StencilOpSeparate) {
 449       ctx->Driver.StencilOpSeparate(ctx, face, sfail, zfail, zpass);
 450    }
 451 }
 452
 453
 454 /* OpenGL 2.0 */
 455 void GLAPIENTRY
 456 _mesa_StencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask)
 457 {
 458    GET_CURRENT_CONTEXT(ctx);
 459
 460    if (MESA_VERBOSE & VERBOSE_API)
 461       _mesa_debug(ctx, "glStencilFuncSeparate()\n");
 462
 463    if (face != GL_FRONT && face != GL_BACK && face != GL_FRONT_AND_BACK) {
 464       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilFuncSeparate(face)");
 465       return;
 466    }
 467    if (!validate_stencil_func(ctx, func)) {
 468       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilFuncSeparate(func)");
 469       return;
 470    }
 471
 472    FLUSH_VERTICES(ctx, _NEW_STENCIL);
 473
 474    if (face != GL_BACK) {
 475       /* set front */
 476       ctx->Stencil.Function[0] = func;
 477       ctx->Stencil.Ref[0] = ref;
 478       ctx->Stencil.ValueMask[0] = mask;
 479    }
 480    if (face != GL_FRONT) {
 481       /* set back */
 482       ctx->Stencil.Function[1] = func;
 483       ctx->Stencil.Ref[1] = ref;
 484       ctx->Stencil.ValueMask[1] = mask;
 485    }
 486    if (ctx->Driver.StencilFuncSeparate) {
 487       ctx->Driver.StencilFuncSeparate(ctx, face, func, ref, mask);
 488    }
 489 }
 490
 491
 492 /* OpenGL 2.0 */
 493 void GLAPIENTRY
 494 _mesa_StencilMaskSeparate(GLenum face, GLuint mask)
 495 {
 496    GET_CURRENT_CONTEXT(ctx);
 497
 498    if (MESA_VERBOSE & VERBOSE_API)
 499       _mesa_debug(ctx, "glStencilMaskSeparate()\n");
 500
 501    if (face != GL_FRONT && face != GL_BACK && face != GL_FRONT_AND_BACK) {
 502       _mesa_error(ctx, GL_INVALID_ENUM, "glStencilaMaskSeparate(face)");
 503       return;
 504    }
 505
 506    FLUSH_VERTICES(ctx, _NEW_STENCIL);
 507
 508    if (face != GL_BACK) {
 509       ctx->Stencil.WriteMask[0] = mask;
 510    }
 511    if (face != GL_FRONT) {
 512       ctx->Stencil.WriteMask[1] = mask;
 513    }
 514    if (ctx->Driver.StencilMaskSeparate) {
 515       ctx->Driver.StencilMaskSeparate(ctx, face, mask);
 516    }
 517 }
 518
 519
 520 /**
 521  * Update derived stencil state.
 522  */
 523 void
 524 _mesa_update_stencil(struct gl_context *ctx)
 525 {
 526    const GLint face = ctx->Stencil._BackFace;
 527
 528    ctx->Stencil._Enabled = (ctx->Stencil.Enabled &&
 529                             ctx->DrawBuffer->Visual.stencilBits > 0);
 530
 531     ctx->Stencil._TestTwoSide =
 532        ctx->Stencil._Enabled &&
 533        (ctx->Stencil.Function[0] != ctx->Stencil.Function[face] ||
 534         ctx->Stencil.FailFunc[0] != ctx->Stencil.FailFunc[face] ||
 535         ctx->Stencil.ZPassFunc[0] != ctx->Stencil.ZPassFunc[face] ||
 536         ctx->Stencil.ZFailFunc[0] != ctx->Stencil.ZFailFunc[face] ||
 537         ctx->Stencil.Ref[0] != ctx->Stencil.Ref[face] ||
 538         ctx->Stencil.ValueMask[0] != ctx->Stencil.ValueMask[face] ||
 539         ctx->Stencil.WriteMask[0] != ctx->Stencil.WriteMask[face]);
 540
 541    ctx->Stencil._WriteEnabled =
 542       ctx->Stencil._Enabled &&
 543       (ctx->Stencil.WriteMask[0] != 0 ||
 544        (ctx->Stencil._TestTwoSide && ctx->Stencil.WriteMask[face] != 0));
 545 }
 546
 547
 548 /**
 549  * Initialize the context stipple state.
 550  *
 551  * \param ctx GL context.
 552  *
 553  * Initializes __struct gl_contextRec::Stencil attribute group.
 554  */
 555 void
 556 _mesa_init_stencil(struct gl_context *ctx)
 557 {
 558    ctx->Stencil.Enabled = GL_FALSE;
 559    ctx->Stencil.TestTwoSide = GL_FALSE;
 560    ctx->Stencil.ActiveFace = 0;  /* 0 = GL_FRONT, 2 = GL_BACK */
 561    ctx->Stencil.Function[0] = GL_ALWAYS;
 562    ctx->Stencil.Function[1] = GL_ALWAYS;
 563    ctx->Stencil.Function[2] = GL_ALWAYS;
 564    ctx->Stencil.FailFunc[0] = GL_KEEP;
 565    ctx->Stencil.FailFunc[1] = GL_KEEP;
 566    ctx->Stencil.FailFunc[2] = GL_KEEP;
 567    ctx->Stencil.ZPassFunc[0] = GL_KEEP;
 568    ctx->Stencil.ZPassFunc[1] = GL_KEEP;
 569    ctx->Stencil.ZPassFunc[2] = GL_KEEP;
 570    ctx->Stencil.ZFailFunc[0] = GL_KEEP;
 571    ctx->Stencil.ZFailFunc[1] = GL_KEEP;
 572    ctx->Stencil.ZFailFunc[2] = GL_KEEP;
 573    ctx->Stencil.Ref[0] = 0;
 574    ctx->Stencil.Ref[1] = 0;
 575    ctx->Stencil.Ref[2] = 0;
 576
 577    /* 4.1.4 Stencil Test section of the GL-ES 3.0 specification says:
 578     *
 579     *     "In the initial state, [...] the front and back stencil mask are both
 580     *     set to the value 2^s − 1, where s is greater than or equal to the
 581     *     number of bits in the deepest stencil buffer* supported by the GL
 582     *     implementation."
 583     *
 584     * Since the maximum supported precision for stencil buffers is 8 bits,
 585     * mask values should be initialized to 2^8 - 1 = 0xFF.
 586     */
 587    ctx->Stencil.ValueMask[0] = 0xFF;
 588    ctx->Stencil.ValueMask[1] = 0xFF;
 589    ctx->Stencil.ValueMask[2] = 0xFF;
 590    ctx->Stencil.WriteMask[0] = 0xFF;
 591    ctx->Stencil.WriteMask[1] = 0xFF;
 592    ctx->Stencil.WriteMask[2] = 0xFF;
 593
 594    ctx->Stencil.Clear = 0;
 595    ctx->Stencil._BackFace = 1;
 596 }