src/mesa/swrast/s_readpix.c

   1 /*
   2  * Mesa 3-D graphics library
   3  * Version:  6.5.2
   4  *
   5  * Copyright (C) 1999-2006  Brian Paul   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  * BRIAN PAUL 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 #include "glheader.h"
  27 #include "bufferobj.h"
  28 #include "colormac.h"
  29 #include "convolve.h"
  30 #include "context.h"
  31 #include "feedback.h"
  32 #include "image.h"
  33 #include "macros.h"
  34 #include "imports.h"
  35 #include "pixel.h"
  36 #include "state.h"
  37
  38 #include "s_context.h"
  39 #include "s_depth.h"
  40 #include "s_span.h"
  41 #include "s_stencil.h"
  42
  43
  44 /*
  45  * Read a block of color index pixels.
  46  */
  47 static void
  48 read_index_pixels( GLcontext *ctx,
  49                    GLint x, GLint y,
  50                    GLsizei width, GLsizei height,
  51                    GLenum type, GLvoid *pixels,
  52                    const struct gl_pixelstore_attrib *packing )
  53 {
  54    struct gl_renderbuffer *rb = ctx->ReadBuffer->_ColorReadBuffer;
  55    GLint i;
  56
  57    ASSERT(rb);
  58
  59    /* width should never be > MAX_WIDTH since we did clipping earlier */
  60    ASSERT(width <= MAX_WIDTH);
  61
  62    /* process image row by row */
  63    for (i = 0; i < height; i++) {
  64       GLuint index[MAX_WIDTH];
  65       GLvoid *dest;
  66       ASSERT(rb->DataType == GL_UNSIGNED_INT);
  67       rb->GetRow(ctx, rb, width, x, y + i, index);
  68
  69       dest = _mesa_image_address2d(packing, pixels, width, height,
  70                                    GL_COLOR_INDEX, type, i, 0);
  71
  72       _mesa_pack_index_span(ctx, width, type, dest, index,
  73                             &ctx->Pack, ctx->_ImageTransferState);
  74    }
  75 }
  76
  77
  78
  79 /**
  80  * Read pixels for format=GL_DEPTH_COMPONENT.
  81  */
  82 static void
  83 read_depth_pixels( GLcontext *ctx,
  84                    GLint x, GLint y,
  85                    GLsizei width, GLsizei height,
  86                    GLenum type, GLvoid *pixels,
  87                    const struct gl_pixelstore_attrib *packing )
  88 {
  89    struct gl_framebuffer *fb = ctx->ReadBuffer;
  90    struct gl_renderbuffer *rb = fb->_DepthBuffer;
  91    const GLboolean biasOrScale
  92       = ctx->Pixel.DepthScale != 1.0 || ctx->Pixel.DepthBias != 0.0;
  93
  94    /* clipping should have been done already */
  95    ASSERT(x >= 0);
  96    ASSERT(y >= 0);
  97    ASSERT(x + width <= rb->Width);
  98    ASSERT(y + height <= rb->Height);
  99    /* width should never be > MAX_WIDTH since we did clipping earlier */
 100    ASSERT(width <= MAX_WIDTH);
 101
 102    ASSERT(rb);
 103
 104    if (type == GL_UNSIGNED_SHORT && fb->Visual.depthBits == 16
 105        && !biasOrScale && !packing->SwapBytes) {
 106       /* Special case: directly read 16-bit unsigned depth values. */
 107       GLint j;
 108       ASSERT(rb->InternalFormat == GL_DEPTH_COMPONENT16);
 109       ASSERT(rb->DataType == GL_UNSIGNED_SHORT);
 110       for (j = 0; j < height; j++, y++) {
 111          void *dest =_mesa_image_address2d(packing, pixels, width, height,
 112                                            GL_DEPTH_COMPONENT, type, j, 0);
 113          rb->GetRow(ctx, rb, width, x, y, dest);
 114       }
 115    }
 116    else if (type == GL_UNSIGNED_INT && fb->Visual.depthBits == 24
 117             && !biasOrScale && !packing->SwapBytes) {
 118       /* Special case: directly read 24-bit unsigned depth values. */
 119       GLint j;
 120       ASSERT(rb->InternalFormat == GL_DEPTH_COMPONENT32);
 121       ASSERT(rb->DataType == GL_UNSIGNED_INT);
 122       for (j = 0; j < height; j++, y++) {
 123          GLuint *dest = (GLuint *)
 124             _mesa_image_address2d(packing, pixels, width, height,
 125                                   GL_DEPTH_COMPONENT, type, j, 0);
 126          GLint k;
 127          rb->GetRow(ctx, rb, width, x, y, dest);
 128          /* convert range from 24-bit to 32-bit */
 129          for (k = 0; k < width; k++) {
 130             dest[k] = (dest[k] << 8) | (dest[k] >> 24);
 131          }
 132       }
 133    }
 134    else if (type == GL_UNSIGNED_INT && fb->Visual.depthBits == 32
 135             && !biasOrScale && !packing->SwapBytes) {
 136       /* Special case: directly read 32-bit unsigned depth values. */
 137       GLint j;
 138       ASSERT(rb->InternalFormat == GL_DEPTH_COMPONENT32);
 139       ASSERT(rb->DataType == GL_UNSIGNED_INT);
 140       for (j = 0; j < height; j++, y++) {
 141          void *dest = _mesa_image_address2d(packing, pixels, width, height,
 142                                             GL_DEPTH_COMPONENT, type, j, 0);
 143          rb->GetRow(ctx, rb, width, x, y, dest);
 144       }
 145    }
 146    else {
 147       /* General case (slower) */
 148       GLint j;
 149       for (j = 0; j < height; j++, y++) {
 150          GLfloat depthValues[MAX_WIDTH];
 151          GLvoid *dest = _mesa_image_address2d(packing, pixels, width, height,
 152                                               GL_DEPTH_COMPONENT, type, j, 0);
 153          _swrast_read_depth_span_float(ctx, rb, width, x, y, depthValues);
 154          _mesa_pack_depth_span(ctx, width, dest, type, depthValues, packing);
 155       }
 156    }
 157 }
 158
 159
 160 /**
 161  * Read pixels for format=GL_STENCIL_INDEX.
 162  */
 163 static void
 164 read_stencil_pixels( GLcontext *ctx,
 165                      GLint x, GLint y,
 166                      GLsizei width, GLsizei height,
 167                      GLenum type, GLvoid *pixels,
 168                      const struct gl_pixelstore_attrib *packing )
 169 {
 170    struct gl_framebuffer *fb = ctx->ReadBuffer;
 171    struct gl_renderbuffer *rb = fb->_StencilBuffer;
 172    GLint j;
 173
 174    ASSERT(rb);
 175
 176    /* width should never be > MAX_WIDTH since we did clipping earlier */
 177    ASSERT(width <= MAX_WIDTH);
 178
 179    /* process image row by row */
 180    for (j=0;j<height;j++,y++) {
 181       GLvoid *dest;
 182       GLstencil stencil[MAX_WIDTH];
 183
 184       _swrast_read_stencil_span(ctx, rb, width, x, y, stencil);
 185
 186       dest = _mesa_image_address2d(packing, pixels, width, height,
 187                                    GL_STENCIL_INDEX, type, j, 0);
 188
 189       _mesa_pack_stencil_span(ctx, width, type, dest, stencil, packing);
 190    }
 191 }
 192
 193
 194
 195 /**
 196  * Optimized glReadPixels for particular pixel formats when pixel
 197  * scaling, biasing, mapping, etc. are disabled.
 198  */
 199 static GLboolean
 200 fast_read_rgba_pixels( GLcontext *ctx,
 201                        GLint x, GLint y,
 202                        GLsizei width, GLsizei height,
 203                        GLenum format, GLenum type,
 204                        GLvoid *pixels,
 205                        const struct gl_pixelstore_attrib *packing )
 206 {
 207    struct gl_renderbuffer *rb = ctx->ReadBuffer->_ColorReadBuffer;
 208
 209    ASSERT(rb->_BaseFormat == GL_RGBA || rb->_BaseFormat == GL_RGB);
 210
 211    /* clipping should have already been done */
 212    ASSERT(x + width <= rb->Width);
 213    ASSERT(y + height <= rb->Height);
 214
 215    /* check for things we can't handle here */
 216    if (ctx->_ImageTransferState ||
 217        packing->SwapBytes ||
 218        packing->LsbFirst) {
 219       return GL_FALSE;
 220    }
 221
 222    if (format == GL_RGBA && rb->DataType == type) {
 223       const GLint dstStride = _mesa_image_row_stride(packing, width,
 224                                                      format, type);
 225       GLubyte *dest = _mesa_image_address2d(packing, pixels, width, height,
 226                                             format, type, 0, 0);
 227       GLint row;
 228       ASSERT(rb->GetRow);
 229       for (row = 0; row < height; row++) {
 230          rb->GetRow(ctx, rb, width, x, y + row, dest);
 231          dest += dstStride;
 232       }
 233       return GL_TRUE;
 234    }
 235
 236    if (format == GL_RGB &&
 237        rb->DataType == GL_UNSIGNED_BYTE &&
 238        type == GL_UNSIGNED_BYTE) {
 239       const GLint dstStride = _mesa_image_row_stride(packing, width,
 240                                                      format, type);
 241       GLubyte *dest = _mesa_image_address2d(packing, pixels, width, height,
 242                                             format, type, 0, 0);
 243       GLint row;
 244       ASSERT(rb->GetRow);
 245       for (row = 0; row < height; row++) {
 246          GLubyte tempRow[MAX_WIDTH][4];
 247          GLint col;
 248          rb->GetRow(ctx, rb, width, x, y + row, tempRow);
 249          /* convert RGBA to RGB */
 250          for (col = 0; col < width; col++) {
 251             dest[col * 3 + 0] = tempRow[col][0];
 252             dest[col * 3 + 1] = tempRow[col][1];
 253             dest[col * 3 + 2] = tempRow[col][2];
 254          }
 255          dest += dstStride;
 256       }
 257       return GL_TRUE;
 258    }
 259
 260    /* not handled */
 261    return GL_FALSE;
 262 }
 263
 264
 265 /**
 266  * When we're using a low-precision color buffer (like 16-bit 5/6/5)
 267  * we have to adjust our color values a bit to pass conformance.
 268  * The problem is when a 5 or 6-bit color value is convert to an 8-bit
 269  * value and then a floating point value, the floating point values don't
 270  * increment uniformly as the 5 or 6-bit value is incremented.
 271  *
 272  * This function adjusts floating point values to compensate.
 273  */
 274 static void
 275 adjust_colors(GLcontext *ctx, GLuint n, GLfloat rgba[][4])
 276 {
 277    const GLuint rShift = 8 - ctx->Visual.redBits;
 278    const GLuint gShift = 8 - ctx->Visual.greenBits;
 279    const GLuint bShift = 8 - ctx->Visual.blueBits;
 280    const GLfloat rScale = 1.0F / (GLfloat) ((1 << ctx->Visual.redBits  ) - 1);
 281    const GLfloat gScale = 1.0F / (GLfloat) ((1 << ctx->Visual.greenBits) - 1);
 282    const GLfloat bScale = 1.0F / (GLfloat) ((1 << ctx->Visual.blueBits ) - 1);
 283    GLuint i;
 284    for (i = 0; i < n; i++) {
 285       GLint r, g, b;
 286       /* convert float back to ubyte */
 287       CLAMPED_FLOAT_TO_UBYTE(r, rgba[i][RCOMP]);
 288       CLAMPED_FLOAT_TO_UBYTE(g, rgba[i][GCOMP]);
 289       CLAMPED_FLOAT_TO_UBYTE(b, rgba[i][BCOMP]);
 290       /* using only the N most significant bits of the ubyte value, convert to
 291        * float in [0,1].
 292        */
 293       rgba[i][RCOMP] = (GLfloat) (r >> rShift) * rScale;
 294       rgba[i][GCOMP] = (GLfloat) (g >> gShift) * gScale;
 295       rgba[i][BCOMP] = (GLfloat) (b >> bShift) * bScale;
 296    }
 297 }
 298
 299
 300
 301 /*
 302  * Read R, G, B, A, RGB, L, or LA pixels.
 303  */
 304 static void
 305 read_rgba_pixels( GLcontext *ctx,
 306                   GLint x, GLint y,
 307                   GLsizei width, GLsizei height,
 308                   GLenum format, GLenum type, GLvoid *pixels,
 309                   const struct gl_pixelstore_attrib *packing )
 310 {
 311    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 312    const GLbitfield transferOps = ctx->_ImageTransferState;
 313    struct gl_framebuffer *fb = ctx->ReadBuffer;
 314    struct gl_renderbuffer *rb = fb->_ColorReadBuffer;
 315
 316    ASSERT(rb);
 317
 318    /* Try optimized path first */
 319    if (fast_read_rgba_pixels(ctx, x, y, width, height,
 320                              format, type, pixels, packing)) {
 321       return; /* done! */
 322    }
 323
 324    /* width should never be > MAX_WIDTH since we did clipping earlier */
 325    ASSERT(width <= MAX_WIDTH);
 326
 327    if (ctx->Pixel.Convolution2DEnabled || ctx->Pixel.Separable2DEnabled) {
 328       GLfloat *dest, *src, *tmpImage, *convImage;
 329       GLint row;
 330
 331       tmpImage = (GLfloat *) _mesa_malloc(width * height * 4 * sizeof(GLfloat));
 332       if (!tmpImage) {
 333          _mesa_error(ctx, GL_OUT_OF_MEMORY, "glReadPixels");
 334          return;
 335       }
 336       convImage = (GLfloat *) _mesa_malloc(width * height * 4 * sizeof(GLfloat));
 337       if (!convImage) {
 338          _mesa_free(tmpImage);
 339          _mesa_error(ctx, GL_OUT_OF_MEMORY, "glReadPixels");
 340          return;
 341       }
 342
 343       /* read full RGBA, FLOAT image */
 344       dest = tmpImage;
 345       for (row = 0; row < height; row++, y++) {
 346          if (fb->Visual.rgbMode) {
 347             _swrast_read_rgba_span(ctx, rb, width, x, y, GL_FLOAT, dest);
 348          }
 349          else {
 350             GLuint index[MAX_WIDTH];
 351             ASSERT(rb->DataType == GL_UNSIGNED_INT);
 352             rb->GetRow(ctx, rb, width, x, y, index);
 353             _mesa_apply_ci_transfer_ops(ctx,
 354                                         transferOps & IMAGE_SHIFT_OFFSET_BIT,
 355                                         width, index);
 356             _mesa_map_ci_to_rgba(ctx, width, index, (GLfloat (*)[4]) dest);
 357          }
 358          _mesa_apply_rgba_transfer_ops(ctx,
 359                                       transferOps & IMAGE_PRE_CONVOLUTION_BITS,
 360                                       width, (GLfloat (*)[4]) dest);
 361          dest += width * 4;
 362       }
 363
 364       /* do convolution */
 365       if (ctx->Pixel.Convolution2DEnabled) {
 366          _mesa_convolve_2d_image(ctx, &width, &height, tmpImage, convImage);
 367       }
 368       else {
 369          ASSERT(ctx->Pixel.Separable2DEnabled);
 370          _mesa_convolve_sep_image(ctx, &width, &height, tmpImage, convImage);
 371       }
 372       _mesa_free(tmpImage);
 373
 374       /* finish transfer ops and pack the resulting image */
 375       src = convImage;
 376       for (row = 0; row < height; row++) {
 377          GLvoid *dest;
 378          dest = _mesa_image_address2d(packing, pixels, width, height,
 379                                       format, type, row, 0);
 380          _mesa_pack_rgba_span_float(ctx, width, (GLfloat (*)[4]) src,
 381                                     format, type, dest, packing,
 382                                     transferOps & IMAGE_POST_CONVOLUTION_BITS);
 383          src += width * 4;
 384       }
 385       _mesa_free(convImage);
 386    }
 387    else {
 388       /* no convolution */
 389       const GLint dstStride
 390          = _mesa_image_row_stride(packing, width, format, type);
 391       GLfloat (*rgba)[4] = swrast->SpanArrays->color.sz4.rgba;
 392       GLint row;
 393       GLubyte *dst = _mesa_image_address2d(packing, pixels, width, height,
 394                                            format, type, 0, 0);
 395
 396       for (row = 0; row < height; row++, y++) {
 397
 398          /* Get float rgba pixels */
 399          if (fb->Visual.rgbMode) {
 400             _swrast_read_rgba_span(ctx, rb, width, x, y, GL_FLOAT, rgba);
 401          }
 402          else {
 403             /* read CI and convert to RGBA */
 404             GLuint index[MAX_WIDTH];
 405             ASSERT(rb->DataType == GL_UNSIGNED_INT);
 406             rb->GetRow(ctx, rb, width, x, y, index);
 407             _mesa_apply_ci_transfer_ops(ctx,
 408                                         transferOps & IMAGE_SHIFT_OFFSET_BIT,
 409                                         width, index);
 410             _mesa_map_ci_to_rgba(ctx, width, index, rgba);
 411          }
 412
 413          /* apply fudge factor for shallow color buffers */
 414          if (fb->Visual.redBits < 8 ||
 415              fb->Visual.greenBits < 8 ||
 416              fb->Visual.blueBits < 8) {
 417             adjust_colors(ctx, width, rgba);
 418          }
 419
 420          /* pack the row of RGBA pixels into user's buffer */
 421          _mesa_pack_rgba_span_float(ctx, width, rgba, format, type, dst,
 422                                     packing, ctx->_ImageTransferState);
 423
 424          dst += dstStride;
 425       }
 426    }
 427 }
 428
 429
 430 /**
 431  * Read combined depth/stencil values.
 432  * We'll have already done error checking to be sure the expected
 433  * depth and stencil buffers really exist.
 434  */
 435 static void
 436 read_depth_stencil_pixels(GLcontext *ctx,
 437                           GLint x, GLint y,
 438                           GLsizei width, GLsizei height,
 439                           GLenum type, GLvoid *pixels,
 440                           const struct gl_pixelstore_attrib *packing )
 441 {
 442    const GLboolean scaleOrBias
 443       = ctx->Pixel.DepthScale != 1.0 || ctx->Pixel.DepthBias != 0.0;
 444    const GLboolean stencilTransfer = ctx->Pixel.IndexShift
 445       || ctx->Pixel.IndexOffset || ctx->Pixel.MapStencilFlag;
 446    struct gl_renderbuffer *depthRb, *stencilRb;
 447
 448    depthRb = ctx->ReadBuffer->_DepthBuffer;
 449    stencilRb = ctx->ReadBuffer->_StencilBuffer;
 450
 451    ASSERT(depthRb);
 452    ASSERT(stencilRb);
 453
 454    depthRb = ctx->ReadBuffer->Attachment[BUFFER_DEPTH].Renderbuffer;
 455    stencilRb = ctx->ReadBuffer->Attachment[BUFFER_STENCIL].Renderbuffer;
 456
 457    if (depthRb->_BaseFormat == GL_DEPTH_STENCIL_EXT &&
 458        stencilRb->_BaseFormat == GL_DEPTH_STENCIL_EXT &&
 459        depthRb == stencilRb &&
 460        !scaleOrBias &&
 461        !stencilTransfer) {
 462       /* This is the ideal case.
 463        * Reading GL_DEPTH_STENCIL pixels from combined depth/stencil buffer.
 464        * Plus, no pixel transfer ops to worry about!
 465        */
 466       GLint i;
 467       GLint dstStride = _mesa_image_row_stride(packing, width,
 468                                                GL_DEPTH_STENCIL_EXT, type);
 469       GLubyte *dst = (GLubyte *) _mesa_image_address2d(packing, pixels,
 470                                                        width, height,
 471                                                        GL_DEPTH_STENCIL_EXT,
 472                                                        type, 0, 0);
 473       for (i = 0; i < height; i++) {
 474          depthRb->GetRow(ctx, depthRb, width, x, y + i, dst);
 475          dst += dstStride;
 476       }
 477    }
 478    else {
 479       /* Reading GL_DEPTH_STENCIL pixels from separate depth/stencil buffers,
 480        * or we need pixel transfer.
 481        */
 482       GLint i;
 483       depthRb = ctx->ReadBuffer->_DepthBuffer;
 484       stencilRb = ctx->ReadBuffer->_StencilBuffer;
 485
 486       for (i = 0; i < height; i++) {
 487          GLstencil stencilVals[MAX_WIDTH];
 488
 489          GLuint *depthStencilDst = (GLuint *)
 490             _mesa_image_address2d(packing, pixels, width, height,
 491                                   GL_DEPTH_STENCIL_EXT, type, i, 0);
 492
 493          _swrast_read_stencil_span(ctx, stencilRb, width,
 494                                    x, y + i, stencilVals);
 495
 496          if (!scaleOrBias && !stencilTransfer
 497              && ctx->ReadBuffer->Visual.depthBits == 24) {
 498             /* ideal case */
 499             GLuint zVals[MAX_WIDTH]; /* 24-bit values! */
 500             GLint j;
 501             ASSERT(depthRb->DataType == GL_UNSIGNED_INT);
 502             /* note, we've already been clipped */
 503             depthRb->GetRow(ctx, depthRb, width, x, y + i, zVals);
 504             for (j = 0; j < width; j++) {
 505                depthStencilDst[j] = (zVals[j] << 8) | (stencilVals[j] & 0xff);
 506             }
 507          }
 508          else {
 509             /* general case */
 510             GLfloat depthVals[MAX_WIDTH];
 511             _swrast_read_depth_span_float(ctx, depthRb, width, x, y + i,
 512                                           depthVals);
 513             _mesa_pack_depth_stencil_span(ctx, width, depthStencilDst,
 514                                           depthVals, stencilVals, packing);
 515          }
 516       }
 517    }
 518 }
 519
 520
 521
 522 /**
 523  * Software fallback routine for ctx->Driver.ReadPixels().
 524  * By time we get here, all error checking will have been done.
 525  */
 526 void
 527 _swrast_ReadPixels( GLcontext *ctx,
 528                     GLint x, GLint y, GLsizei width, GLsizei height,
 529                     GLenum format, GLenum type,
 530                     const struct gl_pixelstore_attrib *packing,
 531                     GLvoid *pixels )
 532 {
 533    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 534    struct gl_pixelstore_attrib clippedPacking = *packing;
 535
 536    /* Need to do RENDER_START before clipping or anything else since this
 537     * is where a driver may grab the hw lock and get an updated window
 538     * size.
 539     */
 540    RENDER_START(swrast, ctx);
 541
 542    if (ctx->NewState)
 543       _mesa_update_state(ctx);
 544
 545    if (swrast->NewState)
 546       _swrast_validate_derived( ctx );
 547
 548    /* Do all needed clipping here, so that we can forget about it later */
 549    if (!_mesa_clip_readpixels(ctx, &x, &y, &width, &height, &clippedPacking)) {
 550       /* The ReadPixels region is totally outside the window bounds */
 551       return;
 552    }
 553
 554    if (clippedPacking.BufferObj->Name) {
 555       /* pack into PBO */
 556       GLubyte *buf;
 557       if (!_mesa_validate_pbo_access(2, &clippedPacking, width, height, 1,
 558                                      format, type, pixels)) {
 559          _mesa_error(ctx, GL_INVALID_OPERATION,
 560                      "glReadPixels(invalid PBO access)");
 561          goto end;
 562       }
 563       buf = (GLubyte *) ctx->Driver.MapBuffer(ctx, GL_PIXEL_PACK_BUFFER_EXT,
 564                                               GL_WRITE_ONLY_ARB,
 565                                               clippedPacking.BufferObj);
 566       if (!buf) {
 567          /* buffer is already mapped - that's an error */
 568          _mesa_error(ctx, GL_INVALID_OPERATION, "glReadPixels(PBO is mapped)");
 569          goto end;
 570       }
 571       pixels = ADD_POINTERS(buf, pixels);
 572    }
 573
 574    switch (format) {
 575       case GL_COLOR_INDEX:
 576          read_index_pixels(ctx, x, y, width, height, type, pixels,
 577                            &clippedPacking);
 578          break;
 579       case GL_STENCIL_INDEX:
 580          read_stencil_pixels(ctx, x, y, width, height, type, pixels,
 581                              &clippedPacking);
 582          break;
 583       case GL_DEPTH_COMPONENT:
 584          read_depth_pixels(ctx, x, y, width, height, type, pixels,
 585                            &clippedPacking);
 586          break;
 587       case GL_RED:
 588       case GL_GREEN:
 589       case GL_BLUE:
 590       case GL_ALPHA:
 591       case GL_RGB:
 592       case GL_LUMINANCE:
 593       case GL_LUMINANCE_ALPHA:
 594       case GL_RGBA:
 595       case GL_BGR:
 596       case GL_BGRA:
 597       case GL_ABGR_EXT:
 598          read_rgba_pixels(ctx, x, y, width, height,
 599                           format, type, pixels, &clippedPacking);
 600          break;
 601       case GL_DEPTH_STENCIL_EXT:
 602          read_depth_stencil_pixels(ctx, x, y, width, height,
 603                                    type, pixels, &clippedPacking);
 604          break;
 605       default:
 606          _mesa_problem(ctx, "unexpected format in _swrast_ReadPixels");
 607          /* don't return yet, clean-up */
 608    }
 609
 610
 611 end:
 612    RENDER_FINISH(swrast, ctx);
 613
 614    if (clippedPacking.BufferObj->Name) {
 615       /* done with PBO so unmap it now */
 616       ctx->Driver.UnmapBuffer(ctx, GL_PIXEL_PACK_BUFFER_EXT,
 617                               clippedPacking.BufferObj);
 618    }
 619 }