aboutsummaryrefslogtreecommitdiff
path: root/mesalib/src/mesa/main/buffers.c
blob: 6cbce9d5da2f224be15ec32d346958200e07f848 (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
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
/*
 * Mesa 3-D graphics library
 *
 * 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
 * THE AUTHORS OR COPYRIGHT HOLDERS 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.
 */


/**
 * \file buffers.c
 * glReadBuffer, DrawBuffer functions.
 */



#include "glheader.h"
#include "buffers.h"
#include "colormac.h"
#include "context.h"
#include "enums.h"
#include "fbobject.h"
#include "mtypes.h"


#define BAD_MASK ~0u


/**
 * Return bitmask of BUFFER_BIT_* flags indicating which color buffers are
 * available to the rendering context (for drawing or reading).
 * This depends on the type of framebuffer.  For window system framebuffers
 * we look at the framebuffer's visual.  But for user-create framebuffers we
 * look at the number of supported color attachments.
 * \param fb  the framebuffer to draw to, or read from
 * \return  bitmask of BUFFER_BIT_* flags
 */
static GLbitfield
supported_buffer_bitmask(const struct gl_context *ctx,
                         const struct gl_framebuffer *fb)
{
   GLbitfield mask = 0x0;

   if (_mesa_is_user_fbo(fb)) {
      /* A user-created renderbuffer */
      GLuint i;
      for (i = 0; i < ctx->Const.MaxColorAttachments; i++) {
         mask |= (BUFFER_BIT_COLOR0 << i);
      }
   }
   else {
      /* A window system framebuffer */
      GLint i;
      mask = BUFFER_BIT_FRONT_LEFT; /* always have this */
      if (fb->Visual.stereoMode) {
         mask |= BUFFER_BIT_FRONT_RIGHT;
         if (fb->Visual.doubleBufferMode) {
            mask |= BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
         }
      }
      else if (fb->Visual.doubleBufferMode) {
         mask |= BUFFER_BIT_BACK_LEFT;
      }

      for (i = 0; i < fb->Visual.numAuxBuffers; i++) {
         mask |= (BUFFER_BIT_AUX0 << i);
      }
   }

   return mask;
}


/**
 * Helper routine used by glDrawBuffer and glDrawBuffersARB.
 * Given a GLenum naming one or more color buffers (such as
 * GL_FRONT_AND_BACK), return the corresponding bitmask of BUFFER_BIT_* flags.
 */
static GLbitfield
draw_buffer_enum_to_bitmask(const struct gl_context *ctx, GLenum buffer)
{
   switch (buffer) {
      case GL_NONE:
         return 0;
      case GL_FRONT:
         return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_FRONT_RIGHT;
      case GL_BACK:
         if (_mesa_is_gles3(ctx)) {
            /* Page 181 (page 192 of the PDF) in section 4.2.1 of the OpenGL
             * ES 3.0.1 specification says:
             *
             *     "When draw buffer zero is BACK, color values are written
             *     into the sole buffer for single-buffered contexts, or into
             *     the back buffer for double-buffered contexts."
             *
             * Since there is no stereo rendering in ES 3.0, only return the
             * LEFT bits.  This also satisfies the "n must be 1" requirement.
             */
            if (ctx->DrawBuffer->Visual.doubleBufferMode)
               return BUFFER_BIT_BACK_LEFT;
            return BUFFER_BIT_FRONT_LEFT;
         }
         return BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
      case GL_RIGHT:
         return BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
      case GL_FRONT_RIGHT:
         return BUFFER_BIT_FRONT_RIGHT;
      case GL_BACK_RIGHT:
         return BUFFER_BIT_BACK_RIGHT;
      case GL_BACK_LEFT:
         return BUFFER_BIT_BACK_LEFT;
      case GL_FRONT_AND_BACK:
         return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT
              | BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
      case GL_LEFT:
         return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT;
      case GL_FRONT_LEFT:
         return BUFFER_BIT_FRONT_LEFT;
      case GL_AUX0:
         return BUFFER_BIT_AUX0;
      case GL_AUX1:
      case GL_AUX2:
      case GL_AUX3:
         return 1 << BUFFER_COUNT; /* invalid, but not BAD_MASK */
      case GL_COLOR_ATTACHMENT0_EXT:
         return BUFFER_BIT_COLOR0;
      case GL_COLOR_ATTACHMENT1_EXT:
         return BUFFER_BIT_COLOR1;
      case GL_COLOR_ATTACHMENT2_EXT:
         return BUFFER_BIT_COLOR2;
      case GL_COLOR_ATTACHMENT3_EXT:
         return BUFFER_BIT_COLOR3;
      case GL_COLOR_ATTACHMENT4_EXT:
         return BUFFER_BIT_COLOR4;
      case GL_COLOR_ATTACHMENT5_EXT:
         return BUFFER_BIT_COLOR5;
      case GL_COLOR_ATTACHMENT6_EXT:
         return BUFFER_BIT_COLOR6;
      case GL_COLOR_ATTACHMENT7_EXT:
         return BUFFER_BIT_COLOR7;
      default:
         /* error */
         return BAD_MASK;
   }
}


/**
 * Helper routine used by glReadBuffer.
 * Given a GLenum naming a color buffer, return the index of the corresponding
 * renderbuffer (a BUFFER_* value).
 * return -1 for an invalid buffer.
 */
static GLint
read_buffer_enum_to_index(GLenum buffer)
{
   switch (buffer) {
      case GL_FRONT:
         return BUFFER_FRONT_LEFT;
      case GL_BACK:
         return BUFFER_BACK_LEFT;
      case GL_RIGHT:
         return BUFFER_FRONT_RIGHT;
      case GL_FRONT_RIGHT:
         return BUFFER_FRONT_RIGHT;
      case GL_BACK_RIGHT:
         return BUFFER_BACK_RIGHT;
      case GL_BACK_LEFT:
         return BUFFER_BACK_LEFT;
      case GL_LEFT:
         return BUFFER_FRONT_LEFT;
      case GL_FRONT_LEFT:
         return BUFFER_FRONT_LEFT;
      case GL_AUX0:
         return BUFFER_AUX0;
      case GL_AUX1:
      case GL_AUX2:
      case GL_AUX3:
         return BUFFER_COUNT; /* invalid, but not -1 */
      case GL_COLOR_ATTACHMENT0_EXT:
         return BUFFER_COLOR0;
      case GL_COLOR_ATTACHMENT1_EXT:
         return BUFFER_COLOR1;
      case GL_COLOR_ATTACHMENT2_EXT:
         return BUFFER_COLOR2;
      case GL_COLOR_ATTACHMENT3_EXT:
         return BUFFER_COLOR3;
      case GL_COLOR_ATTACHMENT4_EXT:
         return BUFFER_COLOR4;
      case GL_COLOR_ATTACHMENT5_EXT:
         return BUFFER_COLOR5;
      case GL_COLOR_ATTACHMENT6_EXT:
         return BUFFER_COLOR6;
      case GL_COLOR_ATTACHMENT7_EXT:
         return BUFFER_COLOR7;
      default:
         /* error */
         return -1;
   }
}


/**
 * Called by glDrawBuffer().
 * Specify which renderbuffer(s) to draw into for the first color output.
 * <buffer> can name zero, one, two or four renderbuffers!
 * \sa _mesa_DrawBuffers
 *
 * \param buffer  buffer token such as GL_LEFT or GL_FRONT_AND_BACK, etc.
 *
 * Note that the behaviour of this function depends on whether the
 * current ctx->DrawBuffer is a window-system framebuffer or a user-created
 * framebuffer object.
 *   In the former case, we update the per-context ctx->Color.DrawBuffer
 *   state var _and_ the FB's ColorDrawBuffer state.
 *   In the later case, we update the FB's ColorDrawBuffer state only.
 *
 * Furthermore, upon a MakeCurrent() or BindFramebuffer() call, if the
 * new FB is a window system FB, we need to re-update the FB's
 * ColorDrawBuffer state to match the context.  This is handled in
 * _mesa_update_framebuffer().
 *
 * See the GL_EXT_framebuffer_object spec for more info.
 */
void GLAPIENTRY
_mesa_DrawBuffer(GLenum buffer)
{
   GLbitfield destMask;
   GET_CURRENT_CONTEXT(ctx);

   FLUSH_VERTICES(ctx, 0);

   if (MESA_VERBOSE & VERBOSE_API) {
      _mesa_debug(ctx, "glDrawBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
   }

   if (buffer == GL_NONE) {
      destMask = 0x0;
   }
   else {
      const GLbitfield supportedMask
         = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
      destMask = draw_buffer_enum_to_bitmask(ctx, buffer);
      if (destMask == BAD_MASK) {
         /* totally bogus buffer */
         _mesa_error(ctx, GL_INVALID_ENUM,
                     "glDrawBuffer(buffer=0x%x)", buffer);
         return;
      }
      destMask &= supportedMask;
      if (destMask == 0x0) {
         /* none of the named color buffers exist! */
         _mesa_error(ctx, GL_INVALID_OPERATION,
                     "glDrawBuffer(buffer=0x%x)", buffer);
         return;
      }
   }

   /* if we get here, there's no error so set new state */
   _mesa_drawbuffers(ctx, 1, &buffer, &destMask);

   /*
    * Call device driver function.
    */
   if (ctx->Driver.DrawBuffers)
      ctx->Driver.DrawBuffers(ctx, 1, &buffer);
   else if (ctx->Driver.DrawBuffer)
      ctx->Driver.DrawBuffer(ctx, buffer);
}


/**
 * Called by glDrawBuffersARB; specifies the destination color renderbuffers
 * for N fragment program color outputs.
 * \sa _mesa_DrawBuffer
 * \param n  number of outputs
 * \param buffers  array [n] of renderbuffer names.  Unlike glDrawBuffer, the
 *                 names cannot specify more than one buffer.  For example,
 *                 GL_FRONT_AND_BACK is illegal.
 */
void GLAPIENTRY
_mesa_DrawBuffers(GLsizei n, const GLenum *buffers)
{
   GLint output;
   GLbitfield usedBufferMask, supportedMask;
   GLbitfield destMask[MAX_DRAW_BUFFERS];
   GET_CURRENT_CONTEXT(ctx);

   FLUSH_VERTICES(ctx, 0);

   /* Turns out n==0 is a valid input that should not produce an error.
    * The remaining code below correctly handles the n==0 case.
    *
    * From the OpenGL 3.0 specification, page 258:
    * "An INVALID_VALUE error is generated if n is greater than
    *  MAX_DRAW_BUFFERS."
    */
   if (n < 0 || n > (GLsizei) ctx->Const.MaxDrawBuffers) {
      _mesa_error(ctx, GL_INVALID_VALUE, "glDrawBuffersARB(n)");
      return;
   }

   supportedMask = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
   usedBufferMask = 0x0;

   /* From the ES 3.0 specification, page 180:
    * "If the GL is bound to the default framebuffer, then n must be 1
    *  and the constant must be BACK or NONE."
    */
   if (_mesa_is_gles3(ctx) && _mesa_is_winsys_fbo(ctx->DrawBuffer) &&
       (n != 1 || (buffers[0] != GL_NONE && buffers[0] != GL_BACK))) {
      _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffers(buffer)");
      return;
   }

   /* complicated error checking... */
   for (output = 0; output < n; output++) {
      if (buffers[output] == GL_NONE) {
         destMask[output] = 0x0;
      }
      else {
         /* Page 259 (page 275 of the PDF) in section 4.2.1 of the OpenGL 3.0
          * spec (20080923) says:
          *
          *     "If the GL is bound to a framebuffer object and DrawBuffers is
          *     supplied with [...] COLOR_ATTACHMENTm where m is greater than
          *     or equal to the value of MAX_COLOR_ATTACHMENTS, then the error
          *     INVALID_OPERATION results."
          */
         if (_mesa_is_user_fbo(ctx->DrawBuffer) && buffers[output] >=
             GL_COLOR_ATTACHMENT0 + ctx->Const.MaxDrawBuffers) {
            _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB(buffer)");
            return;
         }

         destMask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);

         /* From the OpenGL 3.0 specification, page 258:
          * "Each buffer listed in bufs must be one of the values from tables
          *  4.5 or 4.6.  Otherwise, an INVALID_ENUM error is generated.
          */
         if (destMask[output] == BAD_MASK) {
            _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
            return;
         }         

         /* From the OpenGL 4.0 specification, page 256:
          * "For both the default framebuffer and framebuffer objects, the
          *  constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK are not
          *  valid in the bufs array passed to DrawBuffers, and will result in
          *  the error INVALID_ENUM. This restriction is because these
          *  constants may themselves refer to multiple buffers, as shown in
          *  table 4.4."
          *  Previous versions of the OpenGL specification say INVALID_OPERATION,
          *  but the Khronos conformance tests expect INVALID_ENUM.
          */
         if (_mesa_bitcount(destMask[output]) > 1) {
            _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
            return;
         }

         /* From the OpenGL 3.0 specification, page 259:
          * "If the GL is bound to the default framebuffer and DrawBuffers is
          *  supplied with a constant (other than NONE) that does not indicate
          *  any of the color buffers allocated to the GL context by the window
          *  system, the error INVALID_OPERATION will be generated.
          *
          *  If the GL is bound to a framebuffer object and DrawBuffers is
          *  supplied with a constant from table 4.6 [...] then the error
          *  INVALID_OPERATION results."
          */
         destMask[output] &= supportedMask;
         if (destMask[output] == 0) {
            _mesa_error(ctx, GL_INVALID_OPERATION,
                        "glDrawBuffersARB(unsupported buffer)");
            return;
         }

         /* ES 3.0 is even more restrictive.  From the ES 3.0 spec, page 180:
          * "If the GL is bound to a framebuffer object, the ith buffer listed
          *  in bufs must be COLOR_ATTACHMENTi or NONE. [...] INVALID_OPERATION."
          */
         if (_mesa_is_gles3(ctx) && _mesa_is_user_fbo(ctx->DrawBuffer) &&
             buffers[output] != GL_NONE &&
             buffers[output] != GL_COLOR_ATTACHMENT0 + output) {
            _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffers(buffer)");
            return;
         }

         /* From the OpenGL 3.0 specification, page 258:
          * "Except for NONE, a buffer may not appear more than once in the
          *  array pointed to by bufs.  Specifying a buffer more then once will
          *  result in the error INVALID_OPERATION."
          */
         if (destMask[output] & usedBufferMask) {
            _mesa_error(ctx, GL_INVALID_OPERATION,
                        "glDrawBuffersARB(duplicated buffer)");
            return;
         }

         /* update bitmask */
         usedBufferMask |= destMask[output];
      }
   }

   /* OK, if we get here, there were no errors so set the new state */
   _mesa_drawbuffers(ctx, n, buffers, destMask);

   /*
    * Call device driver function.  Note that n can be equal to 0,
    * in which case we don't want to reference buffers[0], which
    * may not be valid.
    */
   if (ctx->Driver.DrawBuffers)
      ctx->Driver.DrawBuffers(ctx, n, buffers);
   else if (ctx->Driver.DrawBuffer)
      ctx->Driver.DrawBuffer(ctx, n > 0 ? buffers[0] : GL_NONE);
}


/**
 * Performs necessary state updates when _mesa_drawbuffers makes an
 * actual change.
 */
static void
updated_drawbuffers(struct gl_context *ctx)
{
   FLUSH_VERTICES(ctx, _NEW_BUFFERS);

   if (ctx->API == API_OPENGL_COMPAT && !ctx->Extensions.ARB_ES2_compatibility) {
      struct gl_framebuffer *fb = ctx->DrawBuffer;

      /* Flag the FBO as requiring validation. */
      if (_mesa_is_user_fbo(fb)) {
	 fb->_Status = 0;
      }
   }
}


/**
 * Helper function to set the GL_DRAW_BUFFER state in the context and
 * current FBO.  Called via glDrawBuffer(), glDrawBuffersARB()
 *
 * All error checking will have been done prior to calling this function
 * so nothing should go wrong at this point.
 *
 * \param ctx  current context
 * \param n    number of color outputs to set
 * \param buffers  array[n] of colorbuffer names, like GL_LEFT.
 * \param destMask  array[n] of BUFFER_BIT_* bitmasks which correspond to the
 *                  colorbuffer names.  (i.e. GL_FRONT_AND_BACK =>
 *                  BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT).
 */
void
_mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
                  const GLbitfield *destMask)
{
   struct gl_framebuffer *fb = ctx->DrawBuffer;
   GLbitfield mask[MAX_DRAW_BUFFERS];
   GLuint buf;

   if (!destMask) {
      /* compute destMask values now */
      const GLbitfield supportedMask = supported_buffer_bitmask(ctx, fb);
      GLuint output;
      for (output = 0; output < n; output++) {
         mask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
         ASSERT(mask[output] != BAD_MASK);
         mask[output] &= supportedMask;
      }
      destMask = mask;
   }

   /*
    * If n==1, destMask[0] may have up to four bits set.
    * Otherwise, destMask[x] can only have one bit set.
    */
   if (n == 1) {
      GLuint count = 0, destMask0 = destMask[0];
      while (destMask0) {
         GLint bufIndex = ffs(destMask0) - 1;
         if (fb->_ColorDrawBufferIndexes[count] != bufIndex) {
            updated_drawbuffers(ctx);
            fb->_ColorDrawBufferIndexes[count] = bufIndex;
         }
         count++;
         destMask0 &= ~(1 << bufIndex);
      }
      fb->ColorDrawBuffer[0] = buffers[0];
      fb->_NumColorDrawBuffers = count;
   }
   else {
      GLuint count = 0;
      for (buf = 0; buf < n; buf++ ) {
         if (destMask[buf]) {
            GLint bufIndex = ffs(destMask[buf]) - 1;
            /* only one bit should be set in the destMask[buf] field */
            ASSERT(_mesa_bitcount(destMask[buf]) == 1);
            if (fb->_ColorDrawBufferIndexes[buf] != bufIndex) {
	       updated_drawbuffers(ctx);
               fb->_ColorDrawBufferIndexes[buf] = bufIndex;
            }
            count = buf + 1;
         }
         else {
            if (fb->_ColorDrawBufferIndexes[buf] != -1) {
	       updated_drawbuffers(ctx);
               fb->_ColorDrawBufferIndexes[buf] = -1;
            }
         }
         fb->ColorDrawBuffer[buf] = buffers[buf];
      }
      fb->_NumColorDrawBuffers = count;
   }

   /* set remaining outputs to -1 (GL_NONE) */
   for (buf = fb->_NumColorDrawBuffers; buf < ctx->Const.MaxDrawBuffers; buf++) {
      if (fb->_ColorDrawBufferIndexes[buf] != -1) {
         updated_drawbuffers(ctx);
         fb->_ColorDrawBufferIndexes[buf] = -1;
      }
   }
   for (buf = n; buf < ctx->Const.MaxDrawBuffers; buf++) {
      fb->ColorDrawBuffer[buf] = GL_NONE;
   }

   if (_mesa_is_winsys_fbo(fb)) {
      /* also set context drawbuffer state */
      for (buf = 0; buf < ctx->Const.MaxDrawBuffers; buf++) {
         if (ctx->Color.DrawBuffer[buf] != fb->ColorDrawBuffer[buf]) {
	    updated_drawbuffers(ctx);
            ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
         }
      }
   }
}


/**
 * Update the current drawbuffer's _ColorDrawBufferIndex[] list, etc.
 * from the context's Color.DrawBuffer[] state.
 * Use when changing contexts.
 */
void
_mesa_update_draw_buffers(struct gl_context *ctx)
{
   GLenum buffers[MAX_DRAW_BUFFERS];
   GLuint i;

   /* should be a window system FBO */
   assert(_mesa_is_winsys_fbo(ctx->DrawBuffer));

   for (i = 0; i < ctx->Const.MaxDrawBuffers; i++)
      buffers[i] = ctx->Color.DrawBuffer[i];

   _mesa_drawbuffers(ctx, ctx->Const.MaxDrawBuffers, buffers, NULL);
}


/**
 * Like \sa _mesa_drawbuffers(), this is a helper function for setting
 * GL_READ_BUFFER state in the context and current FBO.
 * \param ctx  the rendering context
 * \param buffer  GL_FRONT, GL_BACK, GL_COLOR_ATTACHMENT0, etc.
 * \param bufferIndex  the numerical index corresponding to 'buffer'
 */
void
_mesa_readbuffer(struct gl_context *ctx, GLenum buffer, GLint bufferIndex)
{
   struct gl_framebuffer *fb = ctx->ReadBuffer;

   if (_mesa_is_winsys_fbo(fb)) {
      /* Only update the per-context READ_BUFFER state if we're bound to
       * a window-system framebuffer.
       */
      ctx->Pixel.ReadBuffer = buffer;
   }

   fb->ColorReadBuffer = buffer;
   fb->_ColorReadBufferIndex = bufferIndex;

   ctx->NewState |= _NEW_BUFFERS;
}



/**
 * Called by glReadBuffer to set the source renderbuffer for reading pixels.
 * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
 */
void GLAPIENTRY
_mesa_ReadBuffer(GLenum buffer)
{
   struct gl_framebuffer *fb;
   GLbitfield supportedMask;
   GLint srcBuffer;
   GET_CURRENT_CONTEXT(ctx);

   FLUSH_VERTICES(ctx, 0);

   if (MESA_VERBOSE & VERBOSE_API)
      _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));

   fb = ctx->ReadBuffer;

   if (MESA_VERBOSE & VERBOSE_API)
      _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));

   if (buffer == GL_NONE) {
      /* This is legal--it means that no buffer should be bound for reading. */
      srcBuffer = -1;
   }
   else {
      /* general case / window-system framebuffer */
      srcBuffer = read_buffer_enum_to_index(buffer);
      if (srcBuffer == -1) {
         _mesa_error(ctx, GL_INVALID_ENUM,
                     "glReadBuffer(buffer=0x%x)", buffer);
         return;
      }
      supportedMask = supported_buffer_bitmask(ctx, fb);
      if (((1 << srcBuffer) & supportedMask) == 0) {
         _mesa_error(ctx, GL_INVALID_OPERATION,
                     "glReadBuffer(buffer=0x%x)", buffer);
         return;
      }
   }

   /* OK, all error checking has been completed now */

   _mesa_readbuffer(ctx, buffer, srcBuffer);

   /*
    * Call device driver function.
    */
   if (ctx->Driver.ReadBuffer)
      (*ctx->Driver.ReadBuffer)(ctx, buffer);
}