src/mesa/main/pixeltransfer.c

   1 /*
   2  * Mesa 3-D graphics library
   3  *
   4  * Copyright (C) 1999-2008  Brian Paul   All Rights Reserved.
   5  * Copyright (C) 2009-2010  VMware, Inc.  All Rights Reserved.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a
   8  * copy of this software and associated documentation files (the "Software"),
   9  * to deal in the Software without restriction, including without limitation
  10  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  11  * and/or sell copies of the Software, and to permit persons to whom the
  12  * Software is furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included
  15  * in all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  18  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  20  * THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
  21  * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  22  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  23  */
  24
  25
  26 /**
  27  * \file pixeltransfer.c
  28  * Pixel transfer operations (scale, bias, table lookups, etc)
  29  */
  30
  31
  32 #include "glheader.h"
  33 #include "colormac.h"
  34 #include "pixeltransfer.h"
  35 #include "imports.h"
  36 #include "mtypes.h"
  37
  38
  39 /*
  40  * Apply scale and bias factors to an array of RGBA pixels.
  41  */
  42 void
  43 _mesa_scale_and_bias_rgba(GLuint n, GLfloat rgba[][4],
  44                           GLfloat rScale, GLfloat gScale,
  45                           GLfloat bScale, GLfloat aScale,
  46                           GLfloat rBias, GLfloat gBias,
  47                           GLfloat bBias, GLfloat aBias)
  48 {
  49    if (rScale != 1.0 || rBias != 0.0) {
  50       GLuint i;
  51       for (i = 0; i < n; i++) {
  52          rgba[i][RCOMP] = rgba[i][RCOMP] * rScale + rBias;
  53       }
  54    }
  55    if (gScale != 1.0 || gBias != 0.0) {
  56       GLuint i;
  57       for (i = 0; i < n; i++) {
  58          rgba[i][GCOMP] = rgba[i][GCOMP] * gScale + gBias;
  59       }
  60    }
  61    if (bScale != 1.0 || bBias != 0.0) {
  62       GLuint i;
  63       for (i = 0; i < n; i++) {
  64          rgba[i][BCOMP] = rgba[i][BCOMP] * bScale + bBias;
  65       }
  66    }
  67    if (aScale != 1.0 || aBias != 0.0) {
  68       GLuint i;
  69       for (i = 0; i < n; i++) {
  70          rgba[i][ACOMP] = rgba[i][ACOMP] * aScale + aBias;
  71       }
  72    }
  73 }
  74
  75
  76 /*
  77  * Apply pixel mapping to an array of floating point RGBA pixels.
  78  */
  79 void
  80 _mesa_map_rgba( const struct gl_context *ctx, GLuint n, GLfloat rgba[][4] )
  81 {
  82    const GLfloat rscale = (GLfloat) (ctx->PixelMaps.RtoR.Size - 1);
  83    const GLfloat gscale = (GLfloat) (ctx->PixelMaps.GtoG.Size - 1);
  84    const GLfloat bscale = (GLfloat) (ctx->PixelMaps.BtoB.Size - 1);
  85    const GLfloat ascale = (GLfloat) (ctx->PixelMaps.AtoA.Size - 1);
  86    const GLfloat *rMap = ctx->PixelMaps.RtoR.Map;
  87    const GLfloat *gMap = ctx->PixelMaps.GtoG.Map;
  88    const GLfloat *bMap = ctx->PixelMaps.BtoB.Map;
  89    const GLfloat *aMap = ctx->PixelMaps.AtoA.Map;
  90    GLuint i;
  91    for (i=0;i<n;i++) {
  92       GLfloat r = CLAMP(rgba[i][RCOMP], 0.0F, 1.0F);
  93       GLfloat g = CLAMP(rgba[i][GCOMP], 0.0F, 1.0F);
  94       GLfloat b = CLAMP(rgba[i][BCOMP], 0.0F, 1.0F);
  95       GLfloat a = CLAMP(rgba[i][ACOMP], 0.0F, 1.0F);
  96       rgba[i][RCOMP] = rMap[IROUND(r * rscale)];
  97       rgba[i][GCOMP] = gMap[IROUND(g * gscale)];
  98       rgba[i][BCOMP] = bMap[IROUND(b * bscale)];
  99       rgba[i][ACOMP] = aMap[IROUND(a * ascale)];
 100    }
 101 }
 102
 103 /**
 104  * Apply a color table lookup to an array of floating point RGBA colors.
 105  */
 106 void
 107 _mesa_lookup_rgba_float(const struct gl_color_table *table,
 108                         GLuint n, GLfloat rgba[][4])
 109 {
 110    const GLint max = table->Size - 1;
 111    const GLfloat scale = (GLfloat) max;
 112    const GLfloat *lut = table->TableF;
 113    GLuint i;
 114
 115    if (!table->TableF || table->Size == 0)
 116       return;
 117
 118    switch (table->_BaseFormat) {
 119       case GL_INTENSITY:
 120          /* replace RGBA with I */
 121          for (i = 0; i < n; i++) {
 122             GLint j = IROUND(rgba[i][RCOMP] * scale);
 123             GLfloat c = lut[CLAMP(j, 0, max)];
 124             rgba[i][RCOMP] =
 125             rgba[i][GCOMP] =
 126             rgba[i][BCOMP] =
 127             rgba[i][ACOMP] = c;
 128          }
 129          break;
 130       case GL_LUMINANCE:
 131          /* replace RGB with L */
 132          for (i = 0; i < n; i++) {
 133             GLint j = IROUND(rgba[i][RCOMP] * scale);
 134             GLfloat c = lut[CLAMP(j, 0, max)];
 135             rgba[i][RCOMP] =
 136             rgba[i][GCOMP] =
 137             rgba[i][BCOMP] = c;
 138          }
 139          break;
 140       case GL_ALPHA:
 141          /* replace A with A */
 142          for (i = 0; i < n; i++) {
 143             GLint j = IROUND(rgba[i][ACOMP] * scale);
 144             rgba[i][ACOMP] = lut[CLAMP(j, 0, max)];
 145          }
 146          break;
 147       case GL_LUMINANCE_ALPHA:
 148          /* replace RGBA with LLLA */
 149          for (i = 0; i < n; i++) {
 150             GLint jL = IROUND(rgba[i][RCOMP] * scale);
 151             GLint jA = IROUND(rgba[i][ACOMP] * scale);
 152             GLfloat luminance, alpha;
 153             jL = CLAMP(jL, 0, max);
 154             jA = CLAMP(jA, 0, max);
 155             luminance = lut[jL * 2 + 0];
 156             alpha     = lut[jA * 2 + 1];
 157             rgba[i][RCOMP] =
 158             rgba[i][GCOMP] =
 159             rgba[i][BCOMP] = luminance;
 160             rgba[i][ACOMP] = alpha;;
 161          }
 162          break;
 163       case GL_RED:
 164          /* replace RGB with RGB */
 165          for (i = 0; i < n; i++) {
 166             GLint jR = IROUND(rgba[i][RCOMP] * scale);
 167             jR = CLAMP(jR, 0, max);
 168             rgba[i][RCOMP] = lut[jR * 3 + 0];
 169          }
 170          break;
 171       case GL_RG:
 172          /* replace RG with RG */
 173          for (i = 0; i < n; i++) {
 174             GLint jR = IROUND(rgba[i][RCOMP] * scale);
 175             GLint jG = IROUND(rgba[i][GCOMP] * scale);
 176             jR = CLAMP(jR, 0, max);
 177             jG = CLAMP(jG, 0, max);
 178             rgba[i][RCOMP] = lut[jR * 3 + 0];
 179             rgba[i][GCOMP] = lut[jG * 3 + 1];
 180          }
 181          break;
 182       case GL_RGB:
 183          /* replace RGB with RGB */
 184          for (i = 0; i < n; i++) {
 185             GLint jR = IROUND(rgba[i][RCOMP] * scale);
 186             GLint jG = IROUND(rgba[i][GCOMP] * scale);
 187             GLint jB = IROUND(rgba[i][BCOMP] * scale);
 188             jR = CLAMP(jR, 0, max);
 189             jG = CLAMP(jG, 0, max);
 190             jB = CLAMP(jB, 0, max);
 191             rgba[i][RCOMP] = lut[jR * 3 + 0];
 192             rgba[i][GCOMP] = lut[jG * 3 + 1];
 193             rgba[i][BCOMP] = lut[jB * 3 + 2];
 194          }
 195          break;
 196       case GL_RGBA:
 197          /* replace RGBA with RGBA */
 198          for (i = 0; i < n; i++) {
 199             GLint jR = IROUND(rgba[i][RCOMP] * scale);
 200             GLint jG = IROUND(rgba[i][GCOMP] * scale);
 201             GLint jB = IROUND(rgba[i][BCOMP] * scale);
 202             GLint jA = IROUND(rgba[i][ACOMP] * scale);
 203             jR = CLAMP(jR, 0, max);
 204             jG = CLAMP(jG, 0, max);
 205             jB = CLAMP(jB, 0, max);
 206             jA = CLAMP(jA, 0, max);
 207             rgba[i][RCOMP] = lut[jR * 4 + 0];
 208             rgba[i][GCOMP] = lut[jG * 4 + 1];
 209             rgba[i][BCOMP] = lut[jB * 4 + 2];
 210             rgba[i][ACOMP] = lut[jA * 4 + 3];
 211          }
 212          break;
 213       default:
 214          _mesa_problem(NULL, "Bad format in _mesa_lookup_rgba_float");
 215          return;
 216    }
 217 }
 218
 219
 220
 221 /**
 222  * Apply a color table lookup to an array of ubyte/RGBA colors.
 223  */
 224 void
 225 _mesa_lookup_rgba_ubyte(const struct gl_color_table *table,
 226                         GLuint n, GLubyte rgba[][4])
 227 {
 228    const GLubyte *lut = table->TableUB;
 229    const GLfloat scale = (GLfloat) (table->Size - 1) / (GLfloat)255.0;
 230    GLuint i;
 231
 232    if (!table->TableUB || table->Size == 0)
 233       return;
 234
 235    switch (table->_BaseFormat) {
 236    case GL_INTENSITY:
 237       /* replace RGBA with I */
 238       if (table->Size == 256) {
 239          for (i = 0; i < n; i++) {
 240             const GLubyte c = lut[rgba[i][RCOMP]];
 241             rgba[i][RCOMP] =
 242             rgba[i][GCOMP] =
 243             rgba[i][BCOMP] =
 244             rgba[i][ACOMP] = c;
 245          }
 246       }
 247       else {
 248          for (i = 0; i < n; i++) {
 249             GLint j = IROUND((GLfloat) rgba[i][RCOMP] * scale);
 250             rgba[i][RCOMP] =
 251             rgba[i][GCOMP] =
 252             rgba[i][BCOMP] =
 253             rgba[i][ACOMP] = lut[j];
 254          }
 255       }
 256       break;
 257    case GL_LUMINANCE:
 258       /* replace RGB with L */
 259       if (table->Size == 256) {
 260          for (i = 0; i < n; i++) {
 261             const GLubyte c = lut[rgba[i][RCOMP]];
 262             rgba[i][RCOMP] =
 263             rgba[i][GCOMP] =
 264             rgba[i][BCOMP] = c;
 265          }
 266       }
 267       else {
 268          for (i = 0; i < n; i++) {
 269             GLint j = IROUND((GLfloat) rgba[i][RCOMP] * scale);
 270             rgba[i][RCOMP] =
 271             rgba[i][GCOMP] =
 272             rgba[i][BCOMP] = lut[j];
 273          }
 274       }
 275       break;
 276    case GL_ALPHA:
 277       /* replace A with A */
 278       if (table->Size == 256) {
 279          for (i = 0; i < n; i++) {
 280             rgba[i][ACOMP] = lut[rgba[i][ACOMP]];
 281          }
 282       }
 283       else {
 284          for (i = 0; i < n; i++) {
 285             GLint j = IROUND((GLfloat) rgba[i][ACOMP] * scale);
 286             rgba[i][ACOMP] = lut[j];
 287          }
 288       }
 289       break;
 290    case GL_LUMINANCE_ALPHA:
 291       /* replace RGBA with LLLA */
 292       if (table->Size == 256) {
 293          for (i = 0; i < n; i++) {
 294             GLubyte l = lut[rgba[i][RCOMP] * 2 + 0];
 295             GLubyte a = lut[rgba[i][ACOMP] * 2 + 1];;
 296             rgba[i][RCOMP] =
 297             rgba[i][GCOMP] =
 298             rgba[i][BCOMP] = l;
 299             rgba[i][ACOMP] = a;
 300          }
 301       }
 302       else {
 303          for (i = 0; i < n; i++) {
 304             GLint jL = IROUND((GLfloat) rgba[i][RCOMP] * scale);
 305             GLint jA = IROUND((GLfloat) rgba[i][ACOMP] * scale);
 306             GLubyte luminance = lut[jL * 2 + 0];
 307             GLubyte alpha     = lut[jA * 2 + 1];
 308             rgba[i][RCOMP] =
 309             rgba[i][GCOMP] =
 310             rgba[i][BCOMP] = luminance;
 311             rgba[i][ACOMP] = alpha;
 312          }
 313       }
 314       break;
 315    case GL_RGB:
 316       if (table->Size == 256) {
 317          for (i = 0; i < n; i++) {
 318             rgba[i][RCOMP] = lut[rgba[i][RCOMP] * 3 + 0];
 319             rgba[i][GCOMP] = lut[rgba[i][GCOMP] * 3 + 1];
 320             rgba[i][BCOMP] = lut[rgba[i][BCOMP] * 3 + 2];
 321          }
 322       }
 323       else {
 324          for (i = 0; i < n; i++) {
 325             GLint jR = IROUND((GLfloat) rgba[i][RCOMP] * scale);
 326             GLint jG = IROUND((GLfloat) rgba[i][GCOMP] * scale);
 327             GLint jB = IROUND((GLfloat) rgba[i][BCOMP] * scale);
 328             rgba[i][RCOMP] = lut[jR * 3 + 0];
 329             rgba[i][GCOMP] = lut[jG * 3 + 1];
 330             rgba[i][BCOMP] = lut[jB * 3 + 2];
 331          }
 332       }
 333       break;
 334    case GL_RGBA:
 335       if (table->Size == 256) {
 336          for (i = 0; i < n; i++) {
 337             rgba[i][RCOMP] = lut[rgba[i][RCOMP] * 4 + 0];
 338             rgba[i][GCOMP] = lut[rgba[i][GCOMP] * 4 + 1];
 339             rgba[i][BCOMP] = lut[rgba[i][BCOMP] * 4 + 2];
 340             rgba[i][ACOMP] = lut[rgba[i][ACOMP] * 4 + 3];
 341          }
 342       }
 343       else {
 344          for (i = 0; i < n; i++) {
 345             GLint jR = IROUND((GLfloat) rgba[i][RCOMP] * scale);
 346             GLint jG = IROUND((GLfloat) rgba[i][GCOMP] * scale);
 347             GLint jB = IROUND((GLfloat) rgba[i][BCOMP] * scale);
 348             GLint jA = IROUND((GLfloat) rgba[i][ACOMP] * scale);
 349             CLAMPED_FLOAT_TO_CHAN(rgba[i][RCOMP], lut[jR * 4 + 0]);
 350             CLAMPED_FLOAT_TO_CHAN(rgba[i][GCOMP], lut[jG * 4 + 1]);
 351             CLAMPED_FLOAT_TO_CHAN(rgba[i][BCOMP], lut[jB * 4 + 2]);
 352             CLAMPED_FLOAT_TO_CHAN(rgba[i][ACOMP], lut[jA * 4 + 3]);
 353          }
 354       }
 355       break;
 356    default:
 357       _mesa_problem(NULL, "Bad format in _mesa_lookup_rgba_chan");
 358       return;
 359    }
 360 }
 361
 362
 363
 364 /*
 365  * Map color indexes to float rgba values.
 366  */
 367 void
 368 _mesa_map_ci_to_rgba( const struct gl_context *ctx, GLuint n,
 369                       const GLuint index[], GLfloat rgba[][4] )
 370 {
 371    GLuint rmask = ctx->PixelMaps.ItoR.Size - 1;
 372    GLuint gmask = ctx->PixelMaps.ItoG.Size - 1;
 373    GLuint bmask = ctx->PixelMaps.ItoB.Size - 1;
 374    GLuint amask = ctx->PixelMaps.ItoA.Size - 1;
 375    const GLfloat *rMap = ctx->PixelMaps.ItoR.Map;
 376    const GLfloat *gMap = ctx->PixelMaps.ItoG.Map;
 377    const GLfloat *bMap = ctx->PixelMaps.ItoB.Map;
 378    const GLfloat *aMap = ctx->PixelMaps.ItoA.Map;
 379    GLuint i;
 380    for (i=0;i<n;i++) {
 381       rgba[i][RCOMP] = rMap[index[i] & rmask];
 382       rgba[i][GCOMP] = gMap[index[i] & gmask];
 383       rgba[i][BCOMP] = bMap[index[i] & bmask];
 384       rgba[i][ACOMP] = aMap[index[i] & amask];
 385    }
 386 }
 387
 388
 389 /**
 390  * Map ubyte color indexes to ubyte/RGBA values.
 391  */
 392 void
 393 _mesa_map_ci8_to_rgba8(const struct gl_context *ctx,
 394                        GLuint n, const GLubyte index[],
 395                        GLubyte rgba[][4])
 396 {
 397    GLuint rmask = ctx->PixelMaps.ItoR.Size - 1;
 398    GLuint gmask = ctx->PixelMaps.ItoG.Size - 1;
 399    GLuint bmask = ctx->PixelMaps.ItoB.Size - 1;
 400    GLuint amask = ctx->PixelMaps.ItoA.Size - 1;
 401    const GLubyte *rMap = ctx->PixelMaps.ItoR.Map8;
 402    const GLubyte *gMap = ctx->PixelMaps.ItoG.Map8;
 403    const GLubyte *bMap = ctx->PixelMaps.ItoB.Map8;
 404    const GLubyte *aMap = ctx->PixelMaps.ItoA.Map8;
 405    GLuint i;
 406    for (i=0;i<n;i++) {
 407       rgba[i][RCOMP] = rMap[index[i] & rmask];
 408       rgba[i][GCOMP] = gMap[index[i] & gmask];
 409       rgba[i][BCOMP] = bMap[index[i] & bmask];
 410       rgba[i][ACOMP] = aMap[index[i] & amask];
 411    }
 412 }
 413
 414
 415 void
 416 _mesa_scale_and_bias_depth(const struct gl_context *ctx, GLuint n,
 417                            GLfloat depthValues[])
 418 {
 419    const GLfloat scale = ctx->Pixel.DepthScale;
 420    const GLfloat bias = ctx->Pixel.DepthBias;
 421    GLuint i;
 422    for (i = 0; i < n; i++) {
 423       GLfloat d = depthValues[i] * scale + bias;
 424       depthValues[i] = CLAMP(d, 0.0F, 1.0F);
 425    }
 426 }
 427
 428
 429 void
 430 _mesa_scale_and_bias_depth_uint(const struct gl_context *ctx, GLuint n,
 431                                 GLuint depthValues[])
 432 {
 433    const GLdouble max = (double) 0xffffffff;
 434    const GLdouble scale = ctx->Pixel.DepthScale;
 435    const GLdouble bias = ctx->Pixel.DepthBias * max;
 436    GLuint i;
 437    for (i = 0; i < n; i++) {
 438       GLdouble d = (GLdouble) depthValues[i] * scale + bias;
 439       d = CLAMP(d, 0.0, max);
 440       depthValues[i] = (GLuint) d;
 441    }
 442 }
 443
 444 /**
 445  * Apply various pixel transfer operations to an array of RGBA pixels
 446  * as indicated by the transferOps bitmask
 447  */
 448 void
 449 _mesa_apply_rgba_transfer_ops(struct gl_context *ctx, GLbitfield transferOps,
 450                               GLuint n, GLfloat rgba[][4])
 451 {
 452    /* scale & bias */
 453    if (transferOps & IMAGE_SCALE_BIAS_BIT) {
 454       _mesa_scale_and_bias_rgba(n, rgba,
 455                                 ctx->Pixel.RedScale, ctx->Pixel.GreenScale,
 456                                 ctx->Pixel.BlueScale, ctx->Pixel.AlphaScale,
 457                                 ctx->Pixel.RedBias, ctx->Pixel.GreenBias,
 458                                 ctx->Pixel.BlueBias, ctx->Pixel.AlphaBias);
 459    }
 460    /* color map lookup */
 461    if (transferOps & IMAGE_MAP_COLOR_BIT) {
 462       _mesa_map_rgba( ctx, n, rgba );
 463    }
 464
 465    /* clamping to [0,1] */
 466    if (transferOps & IMAGE_CLAMP_BIT) {
 467       GLuint i;
 468       for (i = 0; i < n; i++) {
 469          rgba[i][RCOMP] = CLAMP(rgba[i][RCOMP], 0.0F, 1.0F);
 470          rgba[i][GCOMP] = CLAMP(rgba[i][GCOMP], 0.0F, 1.0F);
 471          rgba[i][BCOMP] = CLAMP(rgba[i][BCOMP], 0.0F, 1.0F);
 472          rgba[i][ACOMP] = CLAMP(rgba[i][ACOMP], 0.0F, 1.0F);
 473       }
 474    }
 475 }
 476
 477
 478 /*
 479  * Apply color index shift and offset to an array of pixels.
 480  */
 481 void
 482 _mesa_shift_and_offset_ci(const struct gl_context *ctx,
 483                           GLuint n, GLuint indexes[])
 484 {
 485    GLint shift = ctx->Pixel.IndexShift;
 486    GLint offset = ctx->Pixel.IndexOffset;
 487    GLuint i;
 488    if (shift > 0) {
 489       for (i=0;i<n;i++) {
 490          indexes[i] = (indexes[i] << shift) + offset;
 491       }
 492    }
 493    else if (shift < 0) {
 494       shift = -shift;
 495       for (i=0;i<n;i++) {
 496          indexes[i] = (indexes[i] >> shift) + offset;
 497       }
 498    }
 499    else {
 500       for (i=0;i<n;i++) {
 501          indexes[i] = indexes[i] + offset;
 502       }
 503    }
 504 }
 505
 506
 507
 508 /**
 509  * Apply color index shift, offset and table lookup to an array
 510  * of color indexes;
 511  */
 512 void
 513 _mesa_apply_ci_transfer_ops(const struct gl_context *ctx,
 514                             GLbitfield transferOps,
 515                             GLuint n, GLuint indexes[])
 516 {
 517    if (transferOps & IMAGE_SHIFT_OFFSET_BIT) {
 518       _mesa_shift_and_offset_ci(ctx, n, indexes);
 519    }
 520    if (transferOps & IMAGE_MAP_COLOR_BIT) {
 521       const GLuint mask = ctx->PixelMaps.ItoI.Size - 1;
 522       GLuint i;
 523       for (i = 0; i < n; i++) {
 524          const GLuint j = indexes[i] & mask;
 525          indexes[i] = IROUND(ctx->PixelMaps.ItoI.Map[j]);
 526       }
 527    }
 528 }
 529
 530
 531 /**
 532  * Apply stencil index shift, offset and table lookup to an array
 533  * of stencil values.
 534  */
 535 void
 536 _mesa_apply_stencil_transfer_ops(const struct gl_context *ctx, GLuint n,
 537                                  GLstencil stencil[])
 538 {
 539    if (ctx->Pixel.IndexShift != 0 || ctx->Pixel.IndexOffset != 0) {
 540       const GLint offset = ctx->Pixel.IndexOffset;
 541       GLint shift = ctx->Pixel.IndexShift;
 542       GLuint i;
 543       if (shift > 0) {
 544          for (i = 0; i < n; i++) {
 545             stencil[i] = (stencil[i] << shift) + offset;
 546          }
 547       }
 548       else if (shift < 0) {
 549          shift = -shift;
 550          for (i = 0; i < n; i++) {
 551             stencil[i] = (stencil[i] >> shift) + offset;
 552          }
 553       }
 554       else {
 555          for (i = 0; i < n; i++) {
 556             stencil[i] = stencil[i] + offset;
 557          }
 558       }
 559    }
 560    if (ctx->Pixel.MapStencilFlag) {
 561       GLuint mask = ctx->PixelMaps.StoS.Size - 1;
 562       GLuint i;
 563       for (i = 0; i < n; i++) {
 564          stencil[i] = (GLstencil)ctx->PixelMaps.StoS.Map[ stencil[i] & mask ];
 565       }
 566    }
 567 }