summaryrefslogtreecommitdiff
path: root/src/mesa/swrast/s_readpix.c
blob: 6186f92899efdd47535abc8dc85eec5402c72658 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
/*
 * Mesa 3-D graphics library
 * Version:  6.5.3
 *
 * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */


#include "main/glheader.h"
#include "bufferobj.h"
#include "main/colormac.h"
#include "convolve.h"
#include "main/context.h"
#include "feedback.h"
#include "image.h"
#include "main/macros.h"
#include "main/imports.h"
#include "pixel.h"
#include "state.h"

#include "s_context.h"
#include "s_depth.h"
#include "s_span.h"
#include "s_stencil.h"


/*
 * Read a block of color index pixels.
 */
static void
read_index_pixels( GLcontext *ctx,
                   GLint x, GLint y,
                   GLsizei width, GLsizei height,
                   GLenum type, GLvoid *pixels,
                   const struct gl_pixelstore_attrib *packing )
{
   struct gl_renderbuffer *rb = ctx->ReadBuffer->_ColorReadBuffer;
   GLint i;

   if (!rb)
      return;

   /* width should never be > MAX_WIDTH since we did clipping earlier */
   ASSERT(width <= MAX_WIDTH);

   /* process image row by row */
   for (i = 0; i < height; i++) {
      GLuint index[MAX_WIDTH];
      GLvoid *dest;
      ASSERT(rb->DataType == GL_UNSIGNED_INT);
      rb->GetRow(ctx, rb, width, x, y + i, index);

      dest = _mesa_image_address2d(packing, pixels, width, height,
                                   GL_COLOR_INDEX, type, i, 0);

      _mesa_pack_index_span(ctx, width, type, dest, index,
                            &ctx->Pack, ctx->_ImageTransferState);
   }
}



/**
 * Read pixels for format=GL_DEPTH_COMPONENT.
 */
static void
read_depth_pixels( GLcontext *ctx,
                   GLint x, GLint y,
                   GLsizei width, GLsizei height,
                   GLenum type, GLvoid *pixels,
                   const struct gl_pixelstore_attrib *packing )
{
   struct gl_framebuffer *fb = ctx->ReadBuffer;
   struct gl_renderbuffer *rb = fb->_DepthBuffer;
   const GLboolean biasOrScale
      = ctx->Pixel.DepthScale != 1.0 || ctx->Pixel.DepthBias != 0.0;

   if (!rb)
      return;

   /* clipping should have been done already */
   ASSERT(x >= 0);
   ASSERT(y >= 0);
   ASSERT(x + width <= (GLint) rb->Width);
   ASSERT(y + height <= (GLint) rb->Height);
   /* width should never be > MAX_WIDTH since we did clipping earlier */
   ASSERT(width <= MAX_WIDTH);

   if (type == GL_UNSIGNED_SHORT && fb->Visual.depthBits == 16
       && !biasOrScale && !packing->SwapBytes) {
      /* Special case: directly read 16-bit unsigned depth values. */
      GLint j;
      ASSERT(rb->InternalFormat == GL_DEPTH_COMPONENT16);
      ASSERT(rb->DataType == GL_UNSIGNED_SHORT);
      for (j = 0; j < height; j++, y++) {
         void *dest =_mesa_image_address2d(packing, pixels, width, height,
                                           GL_DEPTH_COMPONENT, type, j, 0);
         rb->GetRow(ctx, rb, width, x, y, dest);
      }
   }
   else if (type == GL_UNSIGNED_INT && fb->Visual.depthBits == 24
            && !biasOrScale && !packing->SwapBytes) {
      /* Special case: directly read 24-bit unsigned depth values. */
      GLint j;
      ASSERT(rb->InternalFormat == GL_DEPTH_COMPONENT24);
      ASSERT(rb->DataType == GL_UNSIGNED_INT);
      for (j = 0; j < height; j++, y++) {
         GLuint *dest = (GLuint *)
            _mesa_image_address2d(packing, pixels, width, height,
                                  GL_DEPTH_COMPONENT, type, j, 0);
         GLint k;
         rb->GetRow(ctx, rb, width, x, y, dest);
         /* convert range from 24-bit to 32-bit */
         for (k = 0; k < width; k++) {
            dest[k] = (dest[k] << 8) | (dest[k] >> 24);
         }
      }
   }
   else if (type == GL_UNSIGNED_INT && fb->Visual.depthBits == 32
            && !biasOrScale && !packing->SwapBytes) {
      /* Special case: directly read 32-bit unsigned depth values. */
      GLint j;
      ASSERT(rb->InternalFormat == GL_DEPTH_COMPONENT32);
      ASSERT(rb->DataType == GL_UNSIGNED_INT);
      for (j = 0; j < height; j++, y++) {
         void *dest = _mesa_image_address2d(packing, pixels, width, height,
                                            GL_DEPTH_COMPONENT, type, j, 0);
         rb->GetRow(ctx, rb, width, x, y, dest);
      }
   }
   else {
      /* General case (slower) */
      GLint j;
      for (j = 0; j < height; j++, y++) {
         GLfloat depthValues[MAX_WIDTH];
         GLvoid *dest = _mesa_image_address2d(packing, pixels, width, height,
                                              GL_DEPTH_COMPONENT, type, j, 0);
         _swrast_read_depth_span_float(ctx, rb, width, x, y, depthValues);
         _mesa_pack_depth_span(ctx, width, dest, type, depthValues, packing);
      }
   }
}


/**
 * Read pixels for format=GL_STENCIL_INDEX.
 */
static void
read_stencil_pixels( GLcontext *ctx,
                     GLint x, GLint y,
                     GLsizei width, GLsizei height,
                     GLenum type, GLvoid *pixels,
                     const struct gl_pixelstore_attrib *packing )
{
   struct gl_framebuffer *fb = ctx->ReadBuffer;
   struct gl_renderbuffer *rb = fb->_StencilBuffer;
   GLint j;

   if (!rb)
      return;

   /* width should never be > MAX_WIDTH since we did clipping earlier */
   ASSERT(width <= MAX_WIDTH);

   /* process image row by row */
   for (j=0;j<height;j++,y++) {
      GLvoid *dest;
      GLstencil stencil[MAX_WIDTH];

      _swrast_read_stencil_span(ctx, rb, width, x, y, stencil);

      dest = _mesa_image_address2d(packing, pixels, width, height,
                                   GL_STENCIL_INDEX, type, j, 0);

      _mesa_pack_stencil_span(ctx, width, type, dest, stencil, packing);
   }
}



/**
 * Optimized glReadPixels for particular pixel formats when pixel
 * scaling, biasing, mapping, etc. are disabled.
 * \return GL_TRUE if success, GL_FALSE if unable to do the readpixels
 */
static GLboolean
fast_read_rgba_pixels( GLcontext *ctx,
                       GLint x, GLint y,
                       GLsizei width, GLsizei height,
                       GLenum format, GLenum type,
                       GLvoid *pixels,
                       const struct gl_pixelstore_attrib *packing,
                       GLbitfield transferOps)
{
   struct gl_renderbuffer *rb = ctx->ReadBuffer->_ColorReadBuffer;

   if (!rb)
      return GL_FALSE;

   ASSERT(rb->_BaseFormat == GL_RGBA || rb->_BaseFormat == GL_RGB);

   /* clipping should have already been done */
   ASSERT(x + width <= (GLint) rb->Width);
   ASSERT(y + height <= (GLint) rb->Height);

   /* check for things we can't handle here */
   if (transferOps ||
       packing->SwapBytes ||
       packing->LsbFirst) {
      return GL_FALSE;
   }

   if (format == GL_RGBA && rb->DataType == type) {
      const GLint dstStride = _mesa_image_row_stride(packing, width,
                                                     format, type);
      GLubyte *dest
         = (GLubyte *) _mesa_image_address2d(packing, pixels, width, height,
                                             format, type, 0, 0);
      GLint row;
      ASSERT(rb->GetRow);
      for (row = 0; row < height; row++) {
         rb->GetRow(ctx, rb, width, x, y + row, dest);
         dest += dstStride;
      }
      return GL_TRUE;
   }

   if (format == GL_RGB &&
       rb->DataType == GL_UNSIGNED_BYTE &&
       type == GL_UNSIGNED_BYTE) {
      const GLint dstStride = _mesa_image_row_stride(packing, width,
                                                     format, type);
      GLubyte *dest
         = (GLubyte *) _mesa_image_address2d(packing, pixels, width, height,
                                             format, type, 0, 0);
      GLint row;
      ASSERT(rb->GetRow);
      for (row = 0; row < height; row++) {
         GLubyte tempRow[MAX_WIDTH][4];
         GLint col;
         rb->GetRow(ctx, rb, width, x, y + row, tempRow);
         /* convert RGBA to RGB */
         for (col = 0; col < width; col++) {
            dest[col * 3 + 0] = tempRow[col][0];
            dest[col * 3 + 1] = tempRow[col][1];
            dest[col * 3 + 2] = tempRow[col][2];
         }
         dest += dstStride;
      }
      return GL_TRUE;
   }

   /* not handled */
   return GL_FALSE;
}


/**
 * When we're using a low-precision color buffer (like 16-bit 5/6/5)
 * we have to adjust our color values a bit to pass conformance.
 * The problem is when a 5 or 6-bit color value is convert to an 8-bit
 * value and then a floating point value, the floating point values don't
 * increment uniformly as the 5 or 6-bit value is incremented.
 *
 * This function adjusts floating point values to compensate.
 */
static void
adjust_colors(GLcontext *ctx, GLuint n, GLfloat rgba[][4])
{
   const GLuint rShift = 8 - ctx->Visual.redBits;
   const GLuint gShift = 8 - ctx->Visual.greenBits;
   const GLuint bShift = 8 - ctx->Visual.blueBits;
   const GLfloat rScale = 1.0F / (GLfloat) ((1 << ctx->Visual.redBits  ) - 1);
   const GLfloat gScale = 1.0F / (GLfloat) ((1 << ctx->Visual.greenBits) - 1);
   const GLfloat bScale = 1.0F / (GLfloat) ((1 << ctx->Visual.blueBits ) - 1);
   GLuint i;
   for (i = 0; i < n; i++) {
      GLint r, g, b;
      /* convert float back to ubyte */
      CLAMPED_FLOAT_TO_UBYTE(r, rgba[i][RCOMP]);
      CLAMPED_FLOAT_TO_UBYTE(g, rgba[i][GCOMP]);
      CLAMPED_FLOAT_TO_UBYTE(b, rgba[i][BCOMP]);
      /* using only the N most significant bits of the ubyte value, convert to
       * float in [0,1].
       */
      rgba[i][RCOMP] = (GLfloat) (r >> rShift) * rScale;
      rgba[i][GCOMP] = (GLfloat) (g >> gShift) * gScale;
      rgba[i][BCOMP] = (GLfloat) (b >> bShift) * bScale;
   }
}



/*
 * Read R, G, B, A, RGB, L, or LA pixels.
 */
static void
read_rgba_pixels( GLcontext *ctx,
                  GLint x, GLint y,
                  GLsizei width, GLsizei height,
                  GLenum format, GLenum type, GLvoid *pixels,
                  const struct gl_pixelstore_attrib *packing )
{
   SWcontext *swrast = SWRAST_CONTEXT(ctx);
   GLbitfield transferOps = ctx->_ImageTransferState;
   struct gl_framebuffer *fb = ctx->ReadBuffer;
   struct gl_renderbuffer *rb = fb->_ColorReadBuffer;

   if (!rb)
      return;

   if (type == GL_FLOAT && ((ctx->Color.ClampReadColor == GL_TRUE) ||
                            (ctx->Color.ClampReadColor == GL_FIXED_ONLY_ARB &&
                             rb->DataType != GL_FLOAT)))
      transferOps |= IMAGE_CLAMP_BIT;

   /* Try optimized path first */
   if (fast_read_rgba_pixels(ctx, x, y, width, height,
                             format, type, pixels, packing, transferOps)) {
      return; /* done! */
   }

   /* width should never be > MAX_WIDTH since we did clipping earlier */
   ASSERT(width <= MAX_WIDTH);

   if (ctx->Pixel.Convolution2DEnabled || ctx->Pixel.Separable2DEnabled) {
      GLfloat *dest, *src, *tmpImage, *convImage;
      GLint row;

      tmpImage = (GLfloat *) _mesa_malloc(width * height * 4 * sizeof(GLfloat));
      if (!tmpImage) {
         _mesa_error(ctx, GL_OUT_OF_MEMORY, "glReadPixels");
         return;
      }
      convImage = (GLfloat *) _mesa_malloc(width * height * 4 * sizeof(GLfloat));
      if (!convImage) {
         _mesa_free(tmpImage);
         _mesa_error(ctx, GL_OUT_OF_MEMORY, "glReadPixels");
         return;
      }

      /* read full RGBA, FLOAT image */
      dest = tmpImage;
      for (row = 0; row < height; row++, y++) {
         if (fb->Visual.rgbMode) {
            _swrast_read_rgba_span(ctx, rb, width, x, y, GL_FLOAT, dest);
         }
         else {
            GLuint index[MAX_WIDTH];
            ASSERT(rb->DataType == GL_UNSIGNED_INT);
            rb->GetRow(ctx, rb, width, x, y, index);
            _mesa_apply_ci_transfer_ops(ctx,
                                        transferOps & IMAGE_SHIFT_OFFSET_BIT,
                                        width, index);
            _mesa_map_ci_to_rgba(ctx, width, index, (GLfloat (*)[4]) dest);
         }
         _mesa_apply_rgba_transfer_ops(ctx, 
                                      transferOps & IMAGE_PRE_CONVOLUTION_BITS,
                                      width, (GLfloat (*)[4]) dest);
         dest += width * 4;
      }

      /* do convolution */
      if (ctx->Pixel.Convolution2DEnabled) {
         _mesa_convolve_2d_image(ctx, &width, &height, tmpImage, convImage);
      }
      else {
         ASSERT(ctx->Pixel.Separable2DEnabled);
         _mesa_convolve_sep_image(ctx, &width, &height, tmpImage, convImage);
      }
      _mesa_free(tmpImage);

      /* finish transfer ops and pack the resulting image */
      src = convImage;
      for (row = 0; row < height; row++) {
         GLvoid *dest;
         dest = _mesa_image_address2d(packing, pixels, width, height,
                                      format, type, row, 0);
         _mesa_pack_rgba_span_float(ctx, width, (GLfloat (*)[4]) src,
                                    format, type, dest, packing,
                                    transferOps & IMAGE_POST_CONVOLUTION_BITS);
         src += width * 4;
      }
      _mesa_free(convImage);
   }
   else {
      /* no convolution */
      const GLint dstStride
         = _mesa_image_row_stride(packing, width, format, type);
      GLfloat (*rgba)[4] = swrast->SpanArrays->attribs[FRAG_ATTRIB_COL0];
      GLint row;
      GLubyte *dst
         = (GLubyte *) _mesa_image_address2d(packing, pixels, width, height,
                                             format, type, 0, 0);

      /* make sure we don't apply 1D convolution */
      transferOps &= ~(IMAGE_CONVOLUTION_BIT |
                       IMAGE_POST_CONVOLUTION_SCALE_BIAS);

      for (row = 0; row < height; row++, y++) {

         /* Get float rgba pixels */
         if (fb->Visual.rgbMode) {
            _swrast_read_rgba_span(ctx, rb, width, x, y, GL_FLOAT, rgba);
         }
         else {
            /* read CI and convert to RGBA */
            GLuint index[MAX_WIDTH];
            ASSERT(rb->DataType == GL_UNSIGNED_INT);
            rb->GetRow(ctx, rb, width, x, y, index);
            _mesa_apply_ci_transfer_ops(ctx,
                                        transferOps & IMAGE_SHIFT_OFFSET_BIT,
                                        width, index);
            _mesa_map_ci_to_rgba(ctx, width, index, rgba);
         }

         /* apply fudge factor for shallow color buffers */
         if (fb->Visual.redBits < 8 ||
             fb->Visual.greenBits < 8 ||
             fb->Visual.blueBits < 8) {
            adjust_colors(ctx, width, rgba);
         }

         /* pack the row of RGBA pixels into user's buffer */
         _mesa_pack_rgba_span_float(ctx, width, rgba, format, type, dst,
                                    packing, transferOps);

         dst += dstStride;
      }
   }
}


/**
 * Read combined depth/stencil values.
 * We'll have already done error checking to be sure the expected
 * depth and stencil buffers really exist.
 */
static void
read_depth_stencil_pixels(GLcontext *ctx,
                          GLint x, GLint y,
                          GLsizei width, GLsizei height,
                          GLenum type, GLvoid *pixels,
                          const struct gl_pixelstore_attrib *packing )
{
   const GLboolean scaleOrBias
      = ctx->Pixel.DepthScale != 1.0 || ctx->Pixel.DepthBias != 0.0;
   const GLboolean stencilTransfer = ctx->Pixel.IndexShift
      || ctx->Pixel.IndexOffset || ctx->Pixel.MapStencilFlag;
   struct gl_renderbuffer *depthRb, *stencilRb;

   depthRb = ctx->ReadBuffer->_DepthBuffer;
   stencilRb = ctx->ReadBuffer->_StencilBuffer;

   if (!depthRb || !stencilRb)
      return;

   depthRb = ctx->ReadBuffer->Attachment[BUFFER_DEPTH].Renderbuffer;
   stencilRb = ctx->ReadBuffer->Attachment[BUFFER_STENCIL].Renderbuffer;

   if (depthRb->_BaseFormat == GL_DEPTH_STENCIL_EXT &&
       stencilRb->_BaseFormat == GL_DEPTH_STENCIL_EXT &&
       depthRb == stencilRb &&
       !scaleOrBias &&
       !stencilTransfer) {
      /* This is the ideal case.
       * Reading GL_DEPTH_STENCIL pixels from combined depth/stencil buffer.
       * Plus, no pixel transfer ops to worry about!
       */
      GLint i;
      GLint dstStride = _mesa_image_row_stride(packing, width,
                                               GL_DEPTH_STENCIL_EXT, type);
      GLubyte *dst = (GLubyte *) _mesa_image_address2d(packing, pixels,
                                                       width, height,
                                                       GL_DEPTH_STENCIL_EXT,
                                                       type, 0, 0);
      for (i = 0; i < height; i++) {
         depthRb->GetRow(ctx, depthRb, width, x, y + i, dst);
         dst += dstStride;
      }
   }
   else {
      /* Reading GL_DEPTH_STENCIL pixels from separate depth/stencil buffers,
       * or we need pixel transfer.
       */
      GLint i;
      depthRb = ctx->ReadBuffer->_DepthBuffer;
      stencilRb = ctx->ReadBuffer->_StencilBuffer;

      for (i = 0; i < height; i++) {
         GLstencil stencilVals[MAX_WIDTH];

         GLuint *depthStencilDst = (GLuint *)
            _mesa_image_address2d(packing, pixels, width, height,
                                  GL_DEPTH_STENCIL_EXT, type, i, 0);

         _swrast_read_stencil_span(ctx, stencilRb, width,
                                   x, y + i, stencilVals);

         if (!scaleOrBias && !stencilTransfer
             && ctx->ReadBuffer->Visual.depthBits == 24) {
            /* ideal case */
            GLuint zVals[MAX_WIDTH]; /* 24-bit values! */
            GLint j;
            ASSERT(depthRb->DataType == GL_UNSIGNED_INT);
            /* note, we've already been clipped */
            depthRb->GetRow(ctx, depthRb, width, x, y + i, zVals);
            for (j = 0; j < width; j++) {
               depthStencilDst[j] = (zVals[j] << 8) | (stencilVals[j] & 0xff);
            }
         }
         else {
            /* general case */
            GLfloat depthVals[MAX_WIDTH];
            _swrast_read_depth_span_float(ctx, depthRb, width, x, y + i,
                                          depthVals);
            _mesa_pack_depth_stencil_span(ctx, width, depthStencilDst,
                                          depthVals, stencilVals, packing);
         }
      }
   }
}



/**
 * Software fallback routine for ctx->Driver.ReadPixels().
 * By time we get here, all error checking will have been done.
 */
void
_swrast_ReadPixels( GLcontext *ctx,
		    GLint x, GLint y, GLsizei width, GLsizei height,
		    GLenum format, GLenum type,
		    const struct gl_pixelstore_attrib *packing,
		    GLvoid *pixels )
{
   SWcontext *swrast = SWRAST_CONTEXT(ctx);
   struct gl_pixelstore_attrib clippedPacking = *packing;

   /* Need to do RENDER_START before clipping or anything else since this
    * is where a driver may grab the hw lock and get an updated window
    * size.
    */
   RENDER_START(swrast, ctx);

   if (ctx->NewState)
      _mesa_update_state(ctx);

   if (swrast->NewState)
      _swrast_validate_derived( ctx );

   /* Do all needed clipping here, so that we can forget about it later */
   if (!_mesa_clip_readpixels(ctx, &x, &y, &width, &height, &clippedPacking)) {
      /* The ReadPixels region is totally outside the window bounds */
      goto end;
   }

   pixels = _mesa_map_readpix_pbo(ctx, &clippedPacking, pixels);
   if (!pixels)
      return;

   switch (format) {
      case GL_COLOR_INDEX:
         read_index_pixels(ctx, x, y, width, height, type, pixels,
                           &clippedPacking);
	 break;
      case GL_STENCIL_INDEX:
	 read_stencil_pixels(ctx, x, y, width, height, type, pixels,
                             &clippedPacking);
         break;
      case GL_DEPTH_COMPONENT:
	 read_depth_pixels(ctx, x, y, width, height, type, pixels,
                           &clippedPacking);
	 break;
      case GL_RED:
      case GL_GREEN:
      case GL_BLUE:
      case GL_ALPHA:
      case GL_RGB:
      case GL_LUMINANCE:
      case GL_LUMINANCE_ALPHA:
      case GL_RGBA:
      case GL_BGR:
      case GL_BGRA:
      case GL_ABGR_EXT:
         read_rgba_pixels(ctx, x, y, width, height,
                          format, type, pixels, &clippedPacking);
	 break;
      case GL_DEPTH_STENCIL_EXT:
         read_depth_stencil_pixels(ctx, x, y, width, height,
                                   type, pixels, &clippedPacking);
         break;
      default:
	 _mesa_problem(ctx, "unexpected format in _swrast_ReadPixels");
         /* don't return yet, clean-up */
   }


end:
   RENDER_FINISH(swrast, ctx);

   _mesa_unmap_readpix_pbo(ctx, &clippedPacking);
}