src/mesa/swrast/s_readpix.c

   1 /*
   2  * Mesa 3-D graphics library
   3  * Version:  7.0.3
   4  *
   5  * Copyright (C) 1999-2007  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 "main/glheader.h"
  27 #include "main/bufferobj.h"
  28 #include "main/colormac.h"
  29 #include "main/convolve.h"
  30 #include "main/context.h"
  31 #include "main/feedback.h"
  32 #include "main/formats.h"
  33 #include "main/image.h"
  34 #include "main/macros.h"
  35 #include "main/imports.h"
  36 #include "main/pixel.h"
  37 #include "main/state.h"
  38
  39 #include "s_context.h"
  40 #include "s_depth.h"
  41 #include "s_span.h"
  42 #include "s_stencil.h"
  43
  44
  45 /*
  46  * Read a block of color index pixels.
  47  */
  48 static void
  49 read_index_pixels( GLcontext *ctx,
  50                    GLint x, GLint y,
  51                    GLsizei width, GLsizei height,
  52                    GLenum type, GLvoid *pixels,
  53                    const struct gl_pixelstore_attrib *packing )
  54 {
  55    struct gl_renderbuffer *rb = ctx->ReadBuffer->_ColorReadBuffer;
  56    GLint i;
  57
  58    if (!rb)
  59       return;
  60
  61    /* width should never be > MAX_WIDTH since we did clipping earlier */
  62    ASSERT(width <= MAX_WIDTH);
  63
  64    /* process image row by row */
  65    for (i = 0; i < height; i++) {
  66       GLuint index[MAX_WIDTH];
  67       GLvoid *dest;
  68       ASSERT(rb->DataType == GL_UNSIGNED_INT);
  69       rb->GetRow(ctx, rb, width, x, y + i, index);
  70
  71       dest = _mesa_image_address2d(packing, pixels, width, height,
  72                                    GL_COLOR_INDEX, type, i, 0);
  73
  74       _mesa_pack_index_span(ctx, width, type, dest, index,
  75                             &ctx->Pack, ctx->_ImageTransferState);
  76    }
  77 }
  78
  79
  80
  81 /**
  82  * Read pixels for format=GL_DEPTH_COMPONENT.
  83  */
  84 static void
  85 read_depth_pixels( GLcontext *ctx,
  86                    GLint x, GLint y,
  87                    GLsizei width, GLsizei height,
  88                    GLenum type, GLvoid *pixels,
  89                    const struct gl_pixelstore_attrib *packing )
  90 {
  91    struct gl_framebuffer *fb = ctx->ReadBuffer;
  92    struct gl_renderbuffer *rb = fb->_DepthBuffer;
  93    const GLboolean biasOrScale
  94       = ctx->Pixel.DepthScale != 1.0 || ctx->Pixel.DepthBias != 0.0;
  95
  96    if (!rb)
  97       return;
  98
  99    /* clipping should have been done already */
 100    ASSERT(x >= 0);
 101    ASSERT(y >= 0);
 102    ASSERT(x + width <= (GLint) rb->Width);
 103    ASSERT(y + height <= (GLint) rb->Height);
 104    /* width should never be > MAX_WIDTH since we did clipping earlier */
 105    ASSERT(width <= MAX_WIDTH);
 106
 107    if (type == GL_UNSIGNED_SHORT && fb->Visual.depthBits == 16
 108        && !biasOrScale && !packing->SwapBytes) {
 109       /* Special case: directly read 16-bit unsigned depth values. */
 110       GLint j;
 111       ASSERT(rb->Format == MESA_FORMAT_Z16);
 112       ASSERT(rb->DataType == GL_UNSIGNED_SHORT);
 113       for (j = 0; j < height; j++, y++) {
 114          void *dest =_mesa_image_address2d(packing, pixels, width, height,
 115                                            GL_DEPTH_COMPONENT, type, j, 0);
 116          rb->GetRow(ctx, rb, width, x, y, dest);
 117       }
 118    }
 119    else if (type == GL_UNSIGNED_INT && fb->Visual.depthBits == 24
 120             && !biasOrScale && !packing->SwapBytes) {
 121       /* Special case: directly read 24-bit unsigned depth values. */
 122       GLint j;
 123       ASSERT(rb->Format == MESA_FORMAT_X8_Z24);
 124       ASSERT(rb->DataType == GL_UNSIGNED_INT);
 125       for (j = 0; j < height; j++, y++) {
 126          GLuint *dest = (GLuint *)
 127             _mesa_image_address2d(packing, pixels, width, height,
 128                                   GL_DEPTH_COMPONENT, type, j, 0);
 129          GLint k;
 130          rb->GetRow(ctx, rb, width, x, y, dest);
 131          /* convert range from 24-bit to 32-bit */
 132          for (k = 0; k < width; k++) {
 133             /* Note: put MSByte of 24-bit value into LSByte */
 134             dest[k] = (dest[k] << 8) | ((dest[k] >> 16) & 0xff);
 135          }
 136       }
 137    }
 138    else if (type == GL_UNSIGNED_INT && fb->Visual.depthBits == 32
 139             && !biasOrScale && !packing->SwapBytes) {
 140       /* Special case: directly read 32-bit unsigned depth values. */
 141       GLint j;
 142       ASSERT(rb->Format == MESA_FORMAT_Z32);
 143       ASSERT(rb->DataType == GL_UNSIGNED_INT);
 144       for (j = 0; j < height; j++, y++) {
 145          void *dest = _mesa_image_address2d(packing, pixels, width, height,
 146                                             GL_DEPTH_COMPONENT, type, j, 0);
 147          rb->GetRow(ctx, rb, width, x, y, dest);
 148       }
 149    }
 150    else {
 151       /* General case (slower) */
 152       GLint j;
 153       for (j = 0; j < height; j++, y++) {
 154          GLfloat depthValues[MAX_WIDTH];
 155          GLvoid *dest = _mesa_image_address2d(packing, pixels, width, height,
 156                                               GL_DEPTH_COMPONENT, type, j, 0);
 157          _swrast_read_depth_span_float(ctx, rb, width, x, y, depthValues);
 158          _mesa_pack_depth_span(ctx, width, dest, type, depthValues, packing);
 159       }
 160    }
 161 }
 162
 163
 164 /**
 165  * Read pixels for format=GL_STENCIL_INDEX.
 166  */
 167 static void
 168 read_stencil_pixels( GLcontext *ctx,
 169                      GLint x, GLint y,
 170                      GLsizei width, GLsizei height,
 171                      GLenum type, GLvoid *pixels,
 172                      const struct gl_pixelstore_attrib *packing )
 173 {
 174    struct gl_framebuffer *fb = ctx->ReadBuffer;
 175    struct gl_renderbuffer *rb = fb->_StencilBuffer;
 176    GLint j;
 177
 178    if (!rb)
 179       return;
 180
 181    /* width should never be > MAX_WIDTH since we did clipping earlier */
 182    ASSERT(width <= MAX_WIDTH);
 183
 184    /* process image row by row */
 185    for (j=0;j<height;j++,y++) {
 186       GLvoid *dest;
 187       GLstencil stencil[MAX_WIDTH];
 188
 189       _swrast_read_stencil_span(ctx, rb, width, x, y, stencil);
 190
 191       dest = _mesa_image_address2d(packing, pixels, width, height,
 192                                    GL_STENCIL_INDEX, type, j, 0);
 193
 194       _mesa_pack_stencil_span(ctx, width, type, dest, stencil, packing);
 195    }
 196 }
 197
 198
 199
 200 /**
 201  * Optimized glReadPixels for particular pixel formats when pixel
 202  * scaling, biasing, mapping, etc. are disabled.
 203  * \return GL_TRUE if success, GL_FALSE if unable to do the readpixels
 204  */
 205 static GLboolean
 206 fast_read_rgba_pixels( GLcontext *ctx,
 207                        GLint x, GLint y,
 208                        GLsizei width, GLsizei height,
 209                        GLenum format, GLenum type,
 210                        GLvoid *pixels,
 211                        const struct gl_pixelstore_attrib *packing,
 212                        GLbitfield transferOps)
 213 {
 214    struct gl_renderbuffer *rb = ctx->ReadBuffer->_ColorReadBuffer;
 215
 216    if (!rb)
 217       return GL_FALSE;
 218
 219    ASSERT(rb->_BaseFormat == GL_RGBA || rb->_BaseFormat == GL_RGB);
 220
 221    /* clipping should have already been done */
 222    ASSERT(x + width <= (GLint) rb->Width);
 223    ASSERT(y + height <= (GLint) rb->Height);
 224
 225    /* check for things we can't handle here */
 226    if (transferOps ||
 227        packing->SwapBytes ||
 228        packing->LsbFirst) {
 229       return GL_FALSE;
 230    }
 231
 232    if (format == GL_RGBA && rb->DataType == type) {
 233       const GLint dstStride = _mesa_image_row_stride(packing, width,
 234                                                      format, type);
 235       GLubyte *dest
 236          = (GLubyte *) _mesa_image_address2d(packing, pixels, width, height,
 237                                              format, type, 0, 0);
 238       GLint row;
 239       ASSERT(rb->GetRow);
 240       for (row = 0; row < height; row++) {
 241          rb->GetRow(ctx, rb, width, x, y + row, dest);
 242          dest += dstStride;
 243       }
 244       return GL_TRUE;
 245    }
 246
 247    if (format == GL_RGB &&
 248        rb->DataType == GL_UNSIGNED_BYTE &&
 249        type == GL_UNSIGNED_BYTE) {
 250       const GLint dstStride = _mesa_image_row_stride(packing, width,
 251                                                      format, type);
 252       GLubyte *dest
 253          = (GLubyte *) _mesa_image_address2d(packing, pixels, width, height,
 254                                              format, type, 0, 0);
 255       GLint row;
 256       ASSERT(rb->GetRow);
 257       for (row = 0; row < height; row++) {
 258          GLubyte tempRow[MAX_WIDTH][4];
 259          GLint col;
 260          rb->GetRow(ctx, rb, width, x, y + row, tempRow);
 261          /* convert RGBA to RGB */
 262          for (col = 0; col < width; col++) {
 263             dest[col * 3 + 0] = tempRow[col][0];
 264             dest[col * 3 + 1] = tempRow[col][1];
 265             dest[col * 3 + 2] = tempRow[col][2];
 266          }
 267          dest += dstStride;
 268       }
 269       return GL_TRUE;
 270    }
 271
 272    /* not handled */
 273    return GL_FALSE;
 274 }
 275
 276
 277 /**
 278  * When we're using a low-precision color buffer (like 16-bit 5/6/5)
 279  * we have to adjust our color values a bit to pass conformance.
 280  * The problem is when a 5 or 6-bit color value is convert to an 8-bit
 281  * value and then a floating point value, the floating point values don't
 282  * increment uniformly as the 5 or 6-bit value is incremented.
 283  *
 284  * This function adjusts floating point values to compensate.
 285  */
 286 static void
 287 adjust_colors(GLcontext *ctx, GLuint n, GLfloat rgba[][4])
 288 {
 289    const GLuint rShift = 8 - ctx->Visual.redBits;
 290    const GLuint gShift = 8 - ctx->Visual.greenBits;
 291    const GLuint bShift = 8 - ctx->Visual.blueBits;
 292    const GLfloat rScale = 1.0F / (GLfloat) ((1 << ctx->Visual.redBits  ) - 1);
 293    const GLfloat gScale = 1.0F / (GLfloat) ((1 << ctx->Visual.greenBits) - 1);
 294    const GLfloat bScale = 1.0F / (GLfloat) ((1 << ctx->Visual.blueBits ) - 1);
 295    GLuint i;
 296    for (i = 0; i < n; i++) {
 297       GLint r, g, b;
 298       /* convert float back to ubyte */
 299       CLAMPED_FLOAT_TO_UBYTE(r, rgba[i][RCOMP]);
 300       CLAMPED_FLOAT_TO_UBYTE(g, rgba[i][GCOMP]);
 301       CLAMPED_FLOAT_TO_UBYTE(b, rgba[i][BCOMP]);
 302       /* using only the N most significant bits of the ubyte value, convert to
 303        * float in [0,1].
 304        */
 305       rgba[i][RCOMP] = (GLfloat) (r >> rShift) * rScale;
 306       rgba[i][GCOMP] = (GLfloat) (g >> gShift) * gScale;
 307       rgba[i][BCOMP] = (GLfloat) (b >> bShift) * bScale;
 308    }
 309 }
 310
 311
 312
 313 /*
 314  * Read R, G, B, A, RGB, L, or LA pixels.
 315  */
 316 static void
 317 read_rgba_pixels( GLcontext *ctx,
 318                   GLint x, GLint y,
 319                   GLsizei width, GLsizei height,
 320                   GLenum format, GLenum type, GLvoid *pixels,
 321                   const struct gl_pixelstore_attrib *packing )
 322 {
 323    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 324    GLbitfield transferOps = ctx->_ImageTransferState;
 325    struct gl_framebuffer *fb = ctx->ReadBuffer;
 326    struct gl_renderbuffer *rb = fb->_ColorReadBuffer;
 327
 328    if (!rb)
 329       return;
 330
 331    if (type == GL_FLOAT && ((ctx->Color.ClampReadColor == GL_TRUE) ||
 332                             (ctx->Color.ClampReadColor == GL_FIXED_ONLY_ARB &&
 333                              rb->DataType != GL_FLOAT)))
 334       transferOps |= IMAGE_CLAMP_BIT;
 335
 336    /* Try optimized path first */
 337    if (fast_read_rgba_pixels(ctx, x, y, width, height,
 338                              format, type, pixels, packing, transferOps)) {
 339       return; /* done! */
 340    }
 341
 342    /* width should never be > MAX_WIDTH since we did clipping earlier */
 343    ASSERT(width <= MAX_WIDTH);
 344
 345    if (ctx->Pixel.Convolution2DEnabled || ctx->Pixel.Separable2DEnabled) {
 346       GLfloat *dest, *src, *tmpImage, *convImage;
 347       GLint row;
 348
 349       tmpImage = (GLfloat *) _mesa_malloc(width * height * 4 * sizeof(GLfloat));
 350       if (!tmpImage) {
 351          _mesa_error(ctx, GL_OUT_OF_MEMORY, "glReadPixels");
 352          return;
 353       }
 354       convImage = (GLfloat *) _mesa_malloc(width * height * 4 * sizeof(GLfloat));
 355       if (!convImage) {
 356          _mesa_free(tmpImage);
 357          _mesa_error(ctx, GL_OUT_OF_MEMORY, "glReadPixels");
 358          return;
 359       }
 360
 361       /* read full RGBA, FLOAT image */
 362       dest = tmpImage;
 363       for (row = 0; row < height; row++, y++) {
 364          if (fb->Visual.rgbMode) {
 365             _swrast_read_rgba_span(ctx, rb, width, x, y, GL_FLOAT, dest);
 366          }
 367          else {
 368             GLuint index[MAX_WIDTH];
 369             ASSERT(rb->DataType == GL_UNSIGNED_INT);
 370             rb->GetRow(ctx, rb, width, x, y, index);
 371             _mesa_apply_ci_transfer_ops(ctx,
 372                                         transferOps & IMAGE_SHIFT_OFFSET_BIT,
 373                                         width, index);
 374             _mesa_map_ci_to_rgba(ctx, width, index, (GLfloat (*)[4]) dest);
 375          }
 376          _mesa_apply_rgba_transfer_ops(ctx,
 377                                       transferOps & IMAGE_PRE_CONVOLUTION_BITS,
 378                                       width, (GLfloat (*)[4]) dest);
 379          dest += width * 4;
 380       }
 381
 382       /* do convolution */
 383       if (ctx->Pixel.Convolution2DEnabled) {
 384          _mesa_convolve_2d_image(ctx, &width, &height, tmpImage, convImage);
 385       }
 386       else {
 387          ASSERT(ctx->Pixel.Separable2DEnabled);
 388          _mesa_convolve_sep_image(ctx, &width, &height, tmpImage, convImage);
 389       }
 390       _mesa_free(tmpImage);
 391
 392       /* finish transfer ops and pack the resulting image */
 393       src = convImage;
 394       for (row = 0; row < height; row++) {
 395          GLvoid *dest;
 396          dest = _mesa_image_address2d(packing, pixels, width, height,
 397                                       format, type, row, 0);
 398          _mesa_pack_rgba_span_float(ctx, width, (GLfloat (*)[4]) src,
 399                                     format, type, dest, packing,
 400                                     transferOps & IMAGE_POST_CONVOLUTION_BITS);
 401          src += width * 4;
 402       }
 403       _mesa_free(convImage);
 404    }
 405    else {
 406       /* no convolution */
 407       const GLint dstStride
 408          = _mesa_image_row_stride(packing, width, format, type);
 409       GLfloat (*rgba)[4] = swrast->SpanArrays->attribs[FRAG_ATTRIB_COL0];
 410       GLint row;
 411       GLubyte *dst
 412          = (GLubyte *) _mesa_image_address2d(packing, pixels, width, height,
 413                                              format, type, 0, 0);
 414
 415       /* make sure we don't apply 1D convolution */
 416       transferOps &= ~(IMAGE_CONVOLUTION_BIT |
 417                        IMAGE_POST_CONVOLUTION_SCALE_BIAS);
 418
 419       for (row = 0; row < height; row++, y++) {
 420
 421          /* Get float rgba pixels */
 422          if (fb->Visual.rgbMode) {
 423             _swrast_read_rgba_span(ctx, rb, width, x, y, GL_FLOAT, rgba);
 424          }
 425          else {
 426             /* read CI and convert to RGBA */
 427             GLuint index[MAX_WIDTH];
 428             ASSERT(rb->DataType == GL_UNSIGNED_INT);
 429             rb->GetRow(ctx, rb, width, x, y, index);
 430             _mesa_apply_ci_transfer_ops(ctx,
 431                                         transferOps & IMAGE_SHIFT_OFFSET_BIT,
 432                                         width, index);
 433             _mesa_map_ci_to_rgba(ctx, width, index, rgba);
 434          }
 435
 436          /* apply fudge factor for shallow color buffers */
 437          if (fb->Visual.redBits < 8 ||
 438              fb->Visual.greenBits < 8 ||
 439              fb->Visual.blueBits < 8) {
 440             adjust_colors(ctx, width, rgba);
 441          }
 442
 443          /* pack the row of RGBA pixels into user's buffer */
 444          _mesa_pack_rgba_span_float(ctx, width, rgba, format, type, dst,
 445                                     packing, transferOps);
 446
 447          dst += dstStride;
 448       }
 449    }
 450 }
 451
 452
 453 /**
 454  * Read combined depth/stencil values.
 455  * We'll have already done error checking to be sure the expected
 456  * depth and stencil buffers really exist.
 457  */
 458 static void
 459 read_depth_stencil_pixels(GLcontext *ctx,
 460                           GLint x, GLint y,
 461                           GLsizei width, GLsizei height,
 462                           GLenum type, GLvoid *pixels,
 463                           const struct gl_pixelstore_attrib *packing )
 464 {
 465    const GLboolean scaleOrBias
 466       = ctx->Pixel.DepthScale != 1.0 || ctx->Pixel.DepthBias != 0.0;
 467    const GLboolean stencilTransfer = ctx->Pixel.IndexShift
 468       || ctx->Pixel.IndexOffset || ctx->Pixel.MapStencilFlag;
 469    struct gl_renderbuffer *depthRb, *stencilRb;
 470
 471    depthRb = ctx->ReadBuffer->_DepthBuffer;
 472    stencilRb = ctx->ReadBuffer->_StencilBuffer;
 473
 474    if (!depthRb || !stencilRb)
 475       return;
 476
 477    depthRb = ctx->ReadBuffer->Attachment[BUFFER_DEPTH].Renderbuffer;
 478    stencilRb = ctx->ReadBuffer->Attachment[BUFFER_STENCIL].Renderbuffer;
 479
 480    if (depthRb->_BaseFormat == GL_DEPTH_STENCIL_EXT &&
 481        stencilRb->_BaseFormat == GL_DEPTH_STENCIL_EXT &&
 482        depthRb == stencilRb &&
 483        !scaleOrBias &&
 484        !stencilTransfer) {
 485       /* This is the ideal case.
 486        * Reading GL_DEPTH_STENCIL pixels from combined depth/stencil buffer.
 487        * Plus, no pixel transfer ops to worry about!
 488        */
 489       GLint i;
 490       GLint dstStride = _mesa_image_row_stride(packing, width,
 491                                                GL_DEPTH_STENCIL_EXT, type);
 492       GLubyte *dst = (GLubyte *) _mesa_image_address2d(packing, pixels,
 493                                                        width, height,
 494                                                        GL_DEPTH_STENCIL_EXT,
 495                                                        type, 0, 0);
 496       for (i = 0; i < height; i++) {
 497          depthRb->GetRow(ctx, depthRb, width, x, y + i, dst);
 498          dst += dstStride;
 499       }
 500    }
 501    else {
 502       /* Reading GL_DEPTH_STENCIL pixels from separate depth/stencil buffers,
 503        * or we need pixel transfer.
 504        */
 505       GLint i;
 506       depthRb = ctx->ReadBuffer->_DepthBuffer;
 507       stencilRb = ctx->ReadBuffer->_StencilBuffer;
 508
 509       for (i = 0; i < height; i++) {
 510          GLstencil stencilVals[MAX_WIDTH];
 511
 512          GLuint *depthStencilDst = (GLuint *)
 513             _mesa_image_address2d(packing, pixels, width, height,
 514                                   GL_DEPTH_STENCIL_EXT, type, i, 0);
 515
 516          _swrast_read_stencil_span(ctx, stencilRb, width,
 517                                    x, y + i, stencilVals);
 518
 519          if (!scaleOrBias && !stencilTransfer
 520              && ctx->ReadBuffer->Visual.depthBits == 24) {
 521             /* ideal case */
 522             GLuint zVals[MAX_WIDTH]; /* 24-bit values! */
 523             GLint j;
 524             ASSERT(depthRb->DataType == GL_UNSIGNED_INT);
 525             /* note, we've already been clipped */
 526             depthRb->GetRow(ctx, depthRb, width, x, y + i, zVals);
 527             for (j = 0; j < width; j++) {
 528                depthStencilDst[j] = (zVals[j] << 8) | (stencilVals[j] & 0xff);
 529             }
 530          }
 531          else {
 532             /* general case */
 533             GLfloat depthVals[MAX_WIDTH];
 534             _swrast_read_depth_span_float(ctx, depthRb, width, x, y + i,
 535                                           depthVals);
 536             _mesa_pack_depth_stencil_span(ctx, width, depthStencilDst,
 537                                           depthVals, stencilVals, packing);
 538          }
 539       }
 540    }
 541 }
 542
 543
 544
 545 /**
 546  * Software fallback routine for ctx->Driver.ReadPixels().
 547  * By time we get here, all error checking will have been done.
 548  */
 549 void
 550 _swrast_ReadPixels( GLcontext *ctx,
 551                     GLint x, GLint y, GLsizei width, GLsizei height,
 552                     GLenum format, GLenum type,
 553                     const struct gl_pixelstore_attrib *packing,
 554                     GLvoid *pixels )
 555 {
 556    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 557    struct gl_pixelstore_attrib clippedPacking = *packing;
 558
 559    if (ctx->NewState)
 560       _mesa_update_state(ctx);
 561
 562    /* Need to do swrast_render_start() before clipping or anything else
 563     * since this is where a driver may grab the hw lock and get an updated
 564     * window size.
 565     */
 566    swrast_render_start(ctx);
 567
 568    if (swrast->NewState)
 569       _swrast_validate_derived( ctx );
 570
 571    /* Do all needed clipping here, so that we can forget about it later */
 572    if (!_mesa_clip_readpixels(ctx, &x, &y, &width, &height, &clippedPacking)) {
 573       /* The ReadPixels region is totally outside the window bounds */
 574       swrast_render_finish(ctx);
 575       return;
 576    }
 577
 578    pixels = _mesa_map_pbo_dest(ctx, &clippedPacking, pixels);
 579    if (!pixels)
 580       return;
 581
 582    switch (format) {
 583       case GL_COLOR_INDEX:
 584          read_index_pixels(ctx, x, y, width, height, type, pixels,
 585                            &clippedPacking);
 586          break;
 587       case GL_STENCIL_INDEX:
 588          read_stencil_pixels(ctx, x, y, width, height, type, pixels,
 589                              &clippedPacking);
 590          break;
 591       case GL_DEPTH_COMPONENT:
 592          read_depth_pixels(ctx, x, y, width, height, type, pixels,
 593                            &clippedPacking);
 594          break;
 595       case GL_RED:
 596       case GL_GREEN:
 597       case GL_BLUE:
 598       case GL_ALPHA:
 599       case GL_RGB:
 600       case GL_LUMINANCE:
 601       case GL_LUMINANCE_ALPHA:
 602       case GL_RGBA:
 603       case GL_BGR:
 604       case GL_BGRA:
 605       case GL_ABGR_EXT:
 606          read_rgba_pixels(ctx, x, y, width, height,
 607                           format, type, pixels, &clippedPacking);
 608          break;
 609       case GL_DEPTH_STENCIL_EXT:
 610          read_depth_stencil_pixels(ctx, x, y, width, height,
 611                                    type, pixels, &clippedPacking);
 612          break;
 613       default:
 614          _mesa_problem(ctx, "unexpected format in _swrast_ReadPixels");
 615          /* don't return yet, clean-up */
 616    }
 617
 618    swrast_render_finish(ctx);
 619
 620    _mesa_unmap_pbo_dest(ctx, &clippedPacking);
 621 }