src/mesa/main/buffers.c

   1 /*
   2  * Mesa 3-D graphics library
   3  *
   4  * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a
   7  * copy of this software and associated documentation files (the "Software"),
   8  * to deal in the Software without restriction, including without limitation
   9  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  10  * and/or sell copies of the Software, and to permit persons to whom the
  11  * Software is furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included
  14  * in all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  17  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  20  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  21  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  22  * OTHER DEALINGS IN THE SOFTWARE.
  23  */
  24
  25
  26 /**
  27  * \file buffers.c
  28  * glReadBuffer, DrawBuffer functions.
  29  */
  30
  31
  32
  33 #include "glheader.h"
  34 #include "buffers.h"
  35 #include "colormac.h"
  36 #include "context.h"
  37 #include "enums.h"
  38 #include "fbobject.h"
  39 #include "mtypes.h"
  40
  41
  42 #define BAD_MASK ~0u
  43
  44
  45 /**
  46  * Return bitmask of BUFFER_BIT_* flags indicating which color buffers are
  47  * available to the rendering context (for drawing or reading).
  48  * This depends on the type of framebuffer.  For window system framebuffers
  49  * we look at the framebuffer's visual.  But for user-create framebuffers we
  50  * look at the number of supported color attachments.
  51  * \param fb  the framebuffer to draw to, or read from
  52  * \return  bitmask of BUFFER_BIT_* flags
  53  */
  54 static GLbitfield
  55 supported_buffer_bitmask(const struct gl_context *ctx,
  56                          const struct gl_framebuffer *fb)
  57 {
  58    GLbitfield mask = 0x0;
  59
  60    if (_mesa_is_user_fbo(fb)) {
  61       /* A user-created renderbuffer */
  62       GLuint i;
  63       for (i = 0; i < ctx->Const.MaxColorAttachments; i++) {
  64          mask |= (BUFFER_BIT_COLOR0 << i);
  65       }
  66    }
  67    else {
  68       /* A window system framebuffer */
  69       GLint i;
  70       mask = BUFFER_BIT_FRONT_LEFT; /* always have this */
  71       if (fb->Visual.stereoMode) {
  72          mask |= BUFFER_BIT_FRONT_RIGHT;
  73          if (fb->Visual.doubleBufferMode) {
  74             mask |= BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
  75          }
  76       }
  77       else if (fb->Visual.doubleBufferMode) {
  78          mask |= BUFFER_BIT_BACK_LEFT;
  79       }
  80
  81       for (i = 0; i < fb->Visual.numAuxBuffers; i++) {
  82          mask |= (BUFFER_BIT_AUX0 << i);
  83       }
  84    }
  85
  86    return mask;
  87 }
  88
  89
  90 /**
  91  * Helper routine used by glDrawBuffer and glDrawBuffersARB.
  92  * Given a GLenum naming one or more color buffers (such as
  93  * GL_FRONT_AND_BACK), return the corresponding bitmask of BUFFER_BIT_* flags.
  94  */
  95 static GLbitfield
  96 draw_buffer_enum_to_bitmask(const struct gl_context *ctx, GLenum buffer)
  97 {
  98    switch (buffer) {
  99       case GL_NONE:
 100          return 0;
 101       case GL_FRONT:
 102          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_FRONT_RIGHT;
 103       case GL_BACK:
 104          if (_mesa_is_gles(ctx)) {
 105             /* Page 181 (page 192 of the PDF) in section 4.2.1 of the OpenGL
 106              * ES 3.0.1 specification says:
 107              *
 108              *     "When draw buffer zero is BACK, color values are written
 109              *     into the sole buffer for single-buffered contexts, or into
 110              *     the back buffer for double-buffered contexts."
 111              *
 112              * Since there is no stereo rendering in ES 3.0, only return the
 113              * LEFT bits.  This also satisfies the "n must be 1" requirement.
 114              *
 115              * We also do this for GLES 1 and 2 because those APIs have no
 116              * concept of selecting the front and back buffer anyway and it's
 117              * convenient to be able to maintain the magic behaviour of
 118              * GL_BACK in that case.
 119              */
 120             if (ctx->DrawBuffer->Visual.doubleBufferMode)
 121                return BUFFER_BIT_BACK_LEFT;
 122             return BUFFER_BIT_FRONT_LEFT;
 123          }
 124          return BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
 125       case GL_RIGHT:
 126          return BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
 127       case GL_FRONT_RIGHT:
 128          return BUFFER_BIT_FRONT_RIGHT;
 129       case GL_BACK_RIGHT:
 130          return BUFFER_BIT_BACK_RIGHT;
 131       case GL_BACK_LEFT:
 132          return BUFFER_BIT_BACK_LEFT;
 133       case GL_FRONT_AND_BACK:
 134          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT
 135               | BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
 136       case GL_LEFT:
 137          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT;
 138       case GL_FRONT_LEFT:
 139          return BUFFER_BIT_FRONT_LEFT;
 140       case GL_AUX0:
 141          return BUFFER_BIT_AUX0;
 142       case GL_AUX1:
 143       case GL_AUX2:
 144       case GL_AUX3:
 145          return 1 << BUFFER_COUNT; /* invalid, but not BAD_MASK */
 146       case GL_COLOR_ATTACHMENT0_EXT:
 147          return BUFFER_BIT_COLOR0;
 148       case GL_COLOR_ATTACHMENT1_EXT:
 149          return BUFFER_BIT_COLOR1;
 150       case GL_COLOR_ATTACHMENT2_EXT:
 151          return BUFFER_BIT_COLOR2;
 152       case GL_COLOR_ATTACHMENT3_EXT:
 153          return BUFFER_BIT_COLOR3;
 154       case GL_COLOR_ATTACHMENT4_EXT:
 155          return BUFFER_BIT_COLOR4;
 156       case GL_COLOR_ATTACHMENT5_EXT:
 157          return BUFFER_BIT_COLOR5;
 158       case GL_COLOR_ATTACHMENT6_EXT:
 159          return BUFFER_BIT_COLOR6;
 160       case GL_COLOR_ATTACHMENT7_EXT:
 161          return BUFFER_BIT_COLOR7;
 162       default:
 163          /* error */
 164          return BAD_MASK;
 165    }
 166 }
 167
 168
 169 /**
 170  * Helper routine used by glReadBuffer.
 171  * Given a GLenum naming a color buffer, return the index of the corresponding
 172  * renderbuffer (a BUFFER_* value).
 173  * return -1 for an invalid buffer.
 174  */
 175 static GLint
 176 read_buffer_enum_to_index(GLenum buffer)
 177 {
 178    switch (buffer) {
 179       case GL_FRONT:
 180          return BUFFER_FRONT_LEFT;
 181       case GL_BACK:
 182          return BUFFER_BACK_LEFT;
 183       case GL_RIGHT:
 184          return BUFFER_FRONT_RIGHT;
 185       case GL_FRONT_RIGHT:
 186          return BUFFER_FRONT_RIGHT;
 187       case GL_BACK_RIGHT:
 188          return BUFFER_BACK_RIGHT;
 189       case GL_BACK_LEFT:
 190          return BUFFER_BACK_LEFT;
 191       case GL_LEFT:
 192          return BUFFER_FRONT_LEFT;
 193       case GL_FRONT_LEFT:
 194          return BUFFER_FRONT_LEFT;
 195       case GL_AUX0:
 196          return BUFFER_AUX0;
 197       case GL_AUX1:
 198       case GL_AUX2:
 199       case GL_AUX3:
 200          return BUFFER_COUNT; /* invalid, but not -1 */
 201       case GL_COLOR_ATTACHMENT0_EXT:
 202          return BUFFER_COLOR0;
 203       case GL_COLOR_ATTACHMENT1_EXT:
 204          return BUFFER_COLOR1;
 205       case GL_COLOR_ATTACHMENT2_EXT:
 206          return BUFFER_COLOR2;
 207       case GL_COLOR_ATTACHMENT3_EXT:
 208          return BUFFER_COLOR3;
 209       case GL_COLOR_ATTACHMENT4_EXT:
 210          return BUFFER_COLOR4;
 211       case GL_COLOR_ATTACHMENT5_EXT:
 212          return BUFFER_COLOR5;
 213       case GL_COLOR_ATTACHMENT6_EXT:
 214          return BUFFER_COLOR6;
 215       case GL_COLOR_ATTACHMENT7_EXT:
 216          return BUFFER_COLOR7;
 217       default:
 218          /* error */
 219          return -1;
 220    }
 221 }
 222
 223
 224 /**
 225  * Called by glDrawBuffer().
 226  * Specify which renderbuffer(s) to draw into for the first color output.
 227  * <buffer> can name zero, one, two or four renderbuffers!
 228  * \sa _mesa_DrawBuffers
 229  *
 230  * \param buffer  buffer token such as GL_LEFT or GL_FRONT_AND_BACK, etc.
 231  *
 232  * Note that the behaviour of this function depends on whether the
 233  * current ctx->DrawBuffer is a window-system framebuffer or a user-created
 234  * framebuffer object.
 235  *   In the former case, we update the per-context ctx->Color.DrawBuffer
 236  *   state var _and_ the FB's ColorDrawBuffer state.
 237  *   In the later case, we update the FB's ColorDrawBuffer state only.
 238  *
 239  * Furthermore, upon a MakeCurrent() or BindFramebuffer() call, if the
 240  * new FB is a window system FB, we need to re-update the FB's
 241  * ColorDrawBuffer state to match the context.  This is handled in
 242  * _mesa_update_framebuffer().
 243  *
 244  * See the GL_EXT_framebuffer_object spec for more info.
 245  */
 246 void GLAPIENTRY
 247 _mesa_DrawBuffer(GLenum buffer)
 248 {
 249    GLbitfield destMask;
 250    GET_CURRENT_CONTEXT(ctx);
 251
 252    FLUSH_VERTICES(ctx, 0);
 253
 254    if (MESA_VERBOSE & VERBOSE_API) {
 255       _mesa_debug(ctx, "glDrawBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 256    }
 257
 258    if (buffer == GL_NONE) {
 259       destMask = 0x0;
 260    }
 261    else {
 262       const GLbitfield supportedMask
 263          = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
 264       destMask = draw_buffer_enum_to_bitmask(ctx, buffer);
 265       if (destMask == BAD_MASK) {
 266          /* totally bogus buffer */
 267          _mesa_error(ctx, GL_INVALID_ENUM,
 268                      "glDrawBuffer(buffer=0x%x)", buffer);
 269          return;
 270       }
 271       destMask &= supportedMask;
 272       if (destMask == 0x0) {
 273          /* none of the named color buffers exist! */
 274          _mesa_error(ctx, GL_INVALID_OPERATION,
 275                      "glDrawBuffer(buffer=0x%x)", buffer);
 276          return;
 277       }
 278    }
 279
 280    /* if we get here, there's no error so set new state */
 281    _mesa_drawbuffers(ctx, 1, &buffer, &destMask);
 282
 283    /*
 284     * Call device driver function.
 285     */
 286    if (ctx->Driver.DrawBuffers)
 287       ctx->Driver.DrawBuffers(ctx, 1, &buffer);
 288    else if (ctx->Driver.DrawBuffer)
 289       ctx->Driver.DrawBuffer(ctx, buffer);
 290 }
 291
 292
 293 /**
 294  * Called by glDrawBuffersARB; specifies the destination color renderbuffers
 295  * for N fragment program color outputs.
 296  * \sa _mesa_DrawBuffer
 297  * \param n  number of outputs
 298  * \param buffers  array [n] of renderbuffer names.  Unlike glDrawBuffer, the
 299  *                 names cannot specify more than one buffer.  For example,
 300  *                 GL_FRONT_AND_BACK is illegal.
 301  */
 302 void GLAPIENTRY
 303 _mesa_DrawBuffers(GLsizei n, const GLenum *buffers)
 304 {
 305    GLint output;
 306    GLbitfield usedBufferMask, supportedMask;
 307    GLbitfield destMask[MAX_DRAW_BUFFERS];
 308    GET_CURRENT_CONTEXT(ctx);
 309
 310    FLUSH_VERTICES(ctx, 0);
 311
 312    /* Turns out n==0 is a valid input that should not produce an error.
 313     * The remaining code below correctly handles the n==0 case.
 314     *
 315     * From the OpenGL 3.0 specification, page 258:
 316     * "An INVALID_VALUE error is generated if n is greater than
 317     *  MAX_DRAW_BUFFERS."
 318     */
 319    if (n < 0 || n > (GLsizei) ctx->Const.MaxDrawBuffers) {
 320       _mesa_error(ctx, GL_INVALID_VALUE, "glDrawBuffersARB(n)");
 321       return;
 322    }
 323
 324    supportedMask = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
 325    usedBufferMask = 0x0;
 326
 327    /* From the ES 3.0 specification, page 180:
 328     * "If the GL is bound to the default framebuffer, then n must be 1
 329     *  and the constant must be BACK or NONE."
 330     */
 331    if (_mesa_is_gles3(ctx) && _mesa_is_winsys_fbo(ctx->DrawBuffer) &&
 332        (n != 1 || (buffers[0] != GL_NONE && buffers[0] != GL_BACK))) {
 333       _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffers(buffer)");
 334       return;
 335    }
 336
 337    /* complicated error checking... */
 338    for (output = 0; output < n; output++) {
 339       if (buffers[output] == GL_NONE) {
 340          destMask[output] = 0x0;
 341       }
 342       else {
 343          /* Page 259 (page 275 of the PDF) in section 4.2.1 of the OpenGL 3.0
 344           * spec (20080923) says:
 345           *
 346           *     "If the GL is bound to a framebuffer object and DrawBuffers is
 347           *     supplied with [...] COLOR_ATTACHMENTm where m is greater than
 348           *     or equal to the value of MAX_COLOR_ATTACHMENTS, then the error
 349           *     INVALID_OPERATION results."
 350           */
 351          if (_mesa_is_user_fbo(ctx->DrawBuffer) && buffers[output] >=
 352              GL_COLOR_ATTACHMENT0 + ctx->Const.MaxDrawBuffers) {
 353             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB(buffer)");
 354             return;
 355          }
 356
 357          destMask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
 358
 359          /* From the OpenGL 3.0 specification, page 258:
 360           * "Each buffer listed in bufs must be one of the values from tables
 361           *  4.5 or 4.6.  Otherwise, an INVALID_ENUM error is generated.
 362           */
 363          if (destMask[output] == BAD_MASK) {
 364             _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
 365             return;
 366          }
 367
 368          /* From the OpenGL 4.0 specification, page 256:
 369           * "For both the default framebuffer and framebuffer objects, the
 370           *  constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK are not
 371           *  valid in the bufs array passed to DrawBuffers, and will result in
 372           *  the error INVALID_ENUM. This restriction is because these
 373           *  constants may themselves refer to multiple buffers, as shown in
 374           *  table 4.4."
 375           *  Previous versions of the OpenGL specification say INVALID_OPERATION,
 376           *  but the Khronos conformance tests expect INVALID_ENUM.
 377           */
 378          if (_mesa_bitcount(destMask[output]) > 1) {
 379             _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
 380             return;
 381          }
 382
 383          /* From the OpenGL 3.0 specification, page 259:
 384           * "If the GL is bound to the default framebuffer and DrawBuffers is
 385           *  supplied with a constant (other than NONE) that does not indicate
 386           *  any of the color buffers allocated to the GL context by the window
 387           *  system, the error INVALID_OPERATION will be generated.
 388           *
 389           *  If the GL is bound to a framebuffer object and DrawBuffers is
 390           *  supplied with a constant from table 4.6 [...] then the error
 391           *  INVALID_OPERATION results."
 392           */
 393          destMask[output] &= supportedMask;
 394          if (destMask[output] == 0) {
 395             _mesa_error(ctx, GL_INVALID_OPERATION,
 396                         "glDrawBuffersARB(unsupported buffer)");
 397             return;
 398          }
 399
 400          /* ES 3.0 is even more restrictive.  From the ES 3.0 spec, page 180:
 401           * "If the GL is bound to a framebuffer object, the ith buffer listed
 402           *  in bufs must be COLOR_ATTACHMENTi or NONE. [...] INVALID_OPERATION."
 403           */
 404          if (_mesa_is_gles3(ctx) && _mesa_is_user_fbo(ctx->DrawBuffer) &&
 405              buffers[output] != GL_NONE &&
 406              buffers[output] != GL_COLOR_ATTACHMENT0 + output) {
 407             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffers(buffer)");
 408             return;
 409          }
 410
 411          /* From the OpenGL 3.0 specification, page 258:
 412           * "Except for NONE, a buffer may not appear more than once in the
 413           *  array pointed to by bufs.  Specifying a buffer more then once will
 414           *  result in the error INVALID_OPERATION."
 415           */
 416          if (destMask[output] & usedBufferMask) {
 417             _mesa_error(ctx, GL_INVALID_OPERATION,
 418                         "glDrawBuffersARB(duplicated buffer)");
 419             return;
 420          }
 421
 422          /* update bitmask */
 423          usedBufferMask |= destMask[output];
 424       }
 425    }
 426
 427    /* OK, if we get here, there were no errors so set the new state */
 428    _mesa_drawbuffers(ctx, n, buffers, destMask);
 429
 430    /*
 431     * Call device driver function.  Note that n can be equal to 0,
 432     * in which case we don't want to reference buffers[0], which
 433     * may not be valid.
 434     */
 435    if (ctx->Driver.DrawBuffers)
 436       ctx->Driver.DrawBuffers(ctx, n, buffers);
 437    else if (ctx->Driver.DrawBuffer)
 438       ctx->Driver.DrawBuffer(ctx, n > 0 ? buffers[0] : GL_NONE);
 439 }
 440
 441
 442 /**
 443  * Performs necessary state updates when _mesa_drawbuffers makes an
 444  * actual change.
 445  */
 446 static void
 447 updated_drawbuffers(struct gl_context *ctx)
 448 {
 449    FLUSH_VERTICES(ctx, _NEW_BUFFERS);
 450
 451    if (ctx->API == API_OPENGL_COMPAT && !ctx->Extensions.ARB_ES2_compatibility) {
 452       struct gl_framebuffer *fb = ctx->DrawBuffer;
 453
 454       /* Flag the FBO as requiring validation. */
 455       if (_mesa_is_user_fbo(fb)) {
 456          fb->_Status = 0;
 457       }
 458    }
 459 }
 460
 461
 462 /**
 463  * Helper function to set the GL_DRAW_BUFFER state in the context and
 464  * current FBO.  Called via glDrawBuffer(), glDrawBuffersARB()
 465  *
 466  * All error checking will have been done prior to calling this function
 467  * so nothing should go wrong at this point.
 468  *
 469  * \param ctx  current context
 470  * \param n    number of color outputs to set
 471  * \param buffers  array[n] of colorbuffer names, like GL_LEFT.
 472  * \param destMask  array[n] of BUFFER_BIT_* bitmasks which correspond to the
 473  *                  colorbuffer names.  (i.e. GL_FRONT_AND_BACK =>
 474  *                  BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT).
 475  */
 476 void
 477 _mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
 478                   const GLbitfield *destMask)
 479 {
 480    struct gl_framebuffer *fb = ctx->DrawBuffer;
 481    GLbitfield mask[MAX_DRAW_BUFFERS];
 482    GLuint buf;
 483
 484    if (!destMask) {
 485       /* compute destMask values now */
 486       const GLbitfield supportedMask = supported_buffer_bitmask(ctx, fb);
 487       GLuint output;
 488       for (output = 0; output < n; output++) {
 489          mask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
 490          ASSERT(mask[output] != BAD_MASK);
 491          mask[output] &= supportedMask;
 492       }
 493       destMask = mask;
 494    }
 495
 496    /*
 497     * If n==1, destMask[0] may have up to four bits set.
 498     * Otherwise, destMask[x] can only have one bit set.
 499     */
 500    if (n == 1) {
 501       GLuint count = 0, destMask0 = destMask[0];
 502       while (destMask0) {
 503          GLint bufIndex = ffs(destMask0) - 1;
 504          if (fb->_ColorDrawBufferIndexes[count] != bufIndex) {
 505             updated_drawbuffers(ctx);
 506             fb->_ColorDrawBufferIndexes[count] = bufIndex;
 507          }
 508          count++;
 509          destMask0 &= ~(1 << bufIndex);
 510       }
 511       fb->ColorDrawBuffer[0] = buffers[0];
 512       fb->_NumColorDrawBuffers = count;
 513    }
 514    else {
 515       GLuint count = 0;
 516       for (buf = 0; buf < n; buf++ ) {
 517          if (destMask[buf]) {
 518             GLint bufIndex = ffs(destMask[buf]) - 1;
 519             /* only one bit should be set in the destMask[buf] field */
 520             ASSERT(_mesa_bitcount(destMask[buf]) == 1);
 521             if (fb->_ColorDrawBufferIndexes[buf] != bufIndex) {
 522                updated_drawbuffers(ctx);
 523                fb->_ColorDrawBufferIndexes[buf] = bufIndex;
 524             }
 525             count = buf + 1;
 526          }
 527          else {
 528             if (fb->_ColorDrawBufferIndexes[buf] != -1) {
 529                updated_drawbuffers(ctx);
 530                fb->_ColorDrawBufferIndexes[buf] = -1;
 531             }
 532          }
 533          fb->ColorDrawBuffer[buf] = buffers[buf];
 534       }
 535       fb->_NumColorDrawBuffers = count;
 536    }
 537
 538    /* set remaining outputs to -1 (GL_NONE) */
 539    for (buf = fb->_NumColorDrawBuffers; buf < ctx->Const.MaxDrawBuffers; buf++) {
 540       if (fb->_ColorDrawBufferIndexes[buf] != -1) {
 541          updated_drawbuffers(ctx);
 542          fb->_ColorDrawBufferIndexes[buf] = -1;
 543       }
 544    }
 545    for (buf = n; buf < ctx->Const.MaxDrawBuffers; buf++) {
 546       fb->ColorDrawBuffer[buf] = GL_NONE;
 547    }
 548
 549    if (_mesa_is_winsys_fbo(fb)) {
 550       /* also set context drawbuffer state */
 551       for (buf = 0; buf < ctx->Const.MaxDrawBuffers; buf++) {
 552          if (ctx->Color.DrawBuffer[buf] != fb->ColorDrawBuffer[buf]) {
 553             updated_drawbuffers(ctx);
 554             ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
 555          }
 556       }
 557    }
 558 }
 559
 560
 561 /**
 562  * Update the current drawbuffer's _ColorDrawBufferIndex[] list, etc.
 563  * from the context's Color.DrawBuffer[] state.
 564  * Use when changing contexts.
 565  */
 566 void
 567 _mesa_update_draw_buffers(struct gl_context *ctx)
 568 {
 569    GLenum buffers[MAX_DRAW_BUFFERS];
 570    GLuint i;
 571
 572    /* should be a window system FBO */
 573    assert(_mesa_is_winsys_fbo(ctx->DrawBuffer));
 574
 575    for (i = 0; i < ctx->Const.MaxDrawBuffers; i++)
 576       buffers[i] = ctx->Color.DrawBuffer[i];
 577
 578    _mesa_drawbuffers(ctx, ctx->Const.MaxDrawBuffers, buffers, NULL);
 579 }
 580
 581
 582 /**
 583  * Like \sa _mesa_drawbuffers(), this is a helper function for setting
 584  * GL_READ_BUFFER state in the context and current FBO.
 585  * \param ctx  the rendering context
 586  * \param buffer  GL_FRONT, GL_BACK, GL_COLOR_ATTACHMENT0, etc.
 587  * \param bufferIndex  the numerical index corresponding to 'buffer'
 588  */
 589 void
 590 _mesa_readbuffer(struct gl_context *ctx, GLenum buffer, GLint bufferIndex)
 591 {
 592    struct gl_framebuffer *fb = ctx->ReadBuffer;
 593
 594    if (_mesa_is_winsys_fbo(fb)) {
 595       /* Only update the per-context READ_BUFFER state if we're bound to
 596        * a window-system framebuffer.
 597        */
 598       ctx->Pixel.ReadBuffer = buffer;
 599    }
 600
 601    fb->ColorReadBuffer = buffer;
 602    fb->_ColorReadBufferIndex = bufferIndex;
 603
 604    ctx->NewState |= _NEW_BUFFERS;
 605 }
 606
 607
 608
 609 /**
 610  * Called by glReadBuffer to set the source renderbuffer for reading pixels.
 611  * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
 612  */
 613 void GLAPIENTRY
 614 _mesa_ReadBuffer(GLenum buffer)
 615 {
 616    struct gl_framebuffer *fb;
 617    GLbitfield supportedMask;
 618    GLint srcBuffer;
 619    GET_CURRENT_CONTEXT(ctx);
 620
 621    FLUSH_VERTICES(ctx, 0);
 622
 623    if (MESA_VERBOSE & VERBOSE_API)
 624       _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 625
 626    fb = ctx->ReadBuffer;
 627
 628    if (MESA_VERBOSE & VERBOSE_API)
 629       _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 630
 631    if (buffer == GL_NONE) {
 632       /* This is legal--it means that no buffer should be bound for reading. */
 633       srcBuffer = -1;
 634    }
 635    else {
 636       /* general case / window-system framebuffer */
 637       srcBuffer = read_buffer_enum_to_index(buffer);
 638       if (srcBuffer == -1) {
 639          _mesa_error(ctx, GL_INVALID_ENUM,
 640                      "glReadBuffer(buffer=0x%x)", buffer);
 641          return;
 642       }
 643       supportedMask = supported_buffer_bitmask(ctx, fb);
 644       if (((1 << srcBuffer) & supportedMask) == 0) {
 645          _mesa_error(ctx, GL_INVALID_OPERATION,
 646                      "glReadBuffer(buffer=0x%x)", buffer);
 647          return;
 648       }
 649    }
 650
 651    /* OK, all error checking has been completed now */
 652
 653    _mesa_readbuffer(ctx, buffer, srcBuffer);
 654
 655    /*
 656     * Call device driver function.
 657     */
 658    if (ctx->Driver.ReadBuffer)
 659       (*ctx->Driver.ReadBuffer)(ctx, buffer);
 660 }