src/mesa/main/buffers.c

   1 /*
   2  * Mesa 3-D graphics library
   3  * Version:  7.1
   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 /**
  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       ASSERT(ctx->Extensions.EXT_framebuffer_object);
  64       for (i = 0; i < ctx->Const.MaxColorAttachments; i++) {
  65          mask |= (BUFFER_BIT_COLOR0 << i);
  66       }
  67    }
  68    else {
  69       /* A window system framebuffer */
  70       GLint i;
  71       mask = BUFFER_BIT_FRONT_LEFT; /* always have this */
  72       if (fb->Visual.stereoMode) {
  73          mask |= BUFFER_BIT_FRONT_RIGHT;
  74          if (fb->Visual.doubleBufferMode) {
  75             mask |= BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
  76          }
  77       }
  78       else if (fb->Visual.doubleBufferMode) {
  79          mask |= BUFFER_BIT_BACK_LEFT;
  80       }
  81
  82       for (i = 0; i < fb->Visual.numAuxBuffers; i++) {
  83          mask |= (BUFFER_BIT_AUX0 << i);
  84       }
  85    }
  86
  87    return mask;
  88 }
  89
  90
  91 /**
  92  * Helper routine used by glDrawBuffer and glDrawBuffersARB.
  93  * Given a GLenum naming one or more color buffers (such as
  94  * GL_FRONT_AND_BACK), return the corresponding bitmask of BUFFER_BIT_* flags.
  95  */
  96 static GLbitfield
  97 draw_buffer_enum_to_bitmask(const struct gl_context *ctx, GLenum buffer)
  98 {
  99    switch (buffer) {
 100       case GL_NONE:
 101          return 0;
 102       case GL_FRONT:
 103          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_FRONT_RIGHT;
 104       case GL_BACK:
 105          if (_mesa_is_gles3(ctx)) {
 106             /* Page 181 (page 192 of the PDF) in section 4.2.1 of the OpenGL
 107              * ES 3.0.1 specification says:
 108              *
 109              *     "When draw buffer zero is BACK, color values are written
 110              *     into the sole buffer for single-buffered contexts, or into
 111              *     the back buffer for double-buffered contexts."
 112              *
 113              * Since there is no stereo rendering in ES 3.0, only return the
 114              * LEFT bits.  This also satisfies the "n must be 1" requirement.
 115              */
 116             if (ctx->DrawBuffer->Visual.doubleBufferMode)
 117                return BUFFER_BIT_BACK_LEFT;
 118             return BUFFER_BIT_FRONT_LEFT;
 119          }
 120          return BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
 121       case GL_RIGHT:
 122          return BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
 123       case GL_FRONT_RIGHT:
 124          return BUFFER_BIT_FRONT_RIGHT;
 125       case GL_BACK_RIGHT:
 126          return BUFFER_BIT_BACK_RIGHT;
 127       case GL_BACK_LEFT:
 128          return BUFFER_BIT_BACK_LEFT;
 129       case GL_FRONT_AND_BACK:
 130          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT
 131               | BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
 132       case GL_LEFT:
 133          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT;
 134       case GL_FRONT_LEFT:
 135          return BUFFER_BIT_FRONT_LEFT;
 136       case GL_AUX0:
 137          return BUFFER_BIT_AUX0;
 138       case GL_AUX1:
 139       case GL_AUX2:
 140       case GL_AUX3:
 141          return 1 << BUFFER_COUNT; /* invalid, but not BAD_MASK */
 142       case GL_COLOR_ATTACHMENT0_EXT:
 143          return BUFFER_BIT_COLOR0;
 144       case GL_COLOR_ATTACHMENT1_EXT:
 145          return BUFFER_BIT_COLOR1;
 146       case GL_COLOR_ATTACHMENT2_EXT:
 147          return BUFFER_BIT_COLOR2;
 148       case GL_COLOR_ATTACHMENT3_EXT:
 149          return BUFFER_BIT_COLOR3;
 150       case GL_COLOR_ATTACHMENT4_EXT:
 151          return BUFFER_BIT_COLOR4;
 152       case GL_COLOR_ATTACHMENT5_EXT:
 153          return BUFFER_BIT_COLOR5;
 154       case GL_COLOR_ATTACHMENT6_EXT:
 155          return BUFFER_BIT_COLOR6;
 156       case GL_COLOR_ATTACHMENT7_EXT:
 157          return BUFFER_BIT_COLOR7;
 158       default:
 159          /* error */
 160          return BAD_MASK;
 161    }
 162 }
 163
 164
 165 /**
 166  * Helper routine used by glReadBuffer.
 167  * Given a GLenum naming a color buffer, return the index of the corresponding
 168  * renderbuffer (a BUFFER_* value).
 169  * return -1 for an invalid buffer.
 170  */
 171 static GLint
 172 read_buffer_enum_to_index(GLenum buffer)
 173 {
 174    switch (buffer) {
 175       case GL_FRONT:
 176          return BUFFER_FRONT_LEFT;
 177       case GL_BACK:
 178          return BUFFER_BACK_LEFT;
 179       case GL_RIGHT:
 180          return BUFFER_FRONT_RIGHT;
 181       case GL_FRONT_RIGHT:
 182          return BUFFER_FRONT_RIGHT;
 183       case GL_BACK_RIGHT:
 184          return BUFFER_BACK_RIGHT;
 185       case GL_BACK_LEFT:
 186          return BUFFER_BACK_LEFT;
 187       case GL_LEFT:
 188          return BUFFER_FRONT_LEFT;
 189       case GL_FRONT_LEFT:
 190          return BUFFER_FRONT_LEFT;
 191       case GL_AUX0:
 192          return BUFFER_AUX0;
 193       case GL_AUX1:
 194       case GL_AUX2:
 195       case GL_AUX3:
 196          return BUFFER_COUNT; /* invalid, but not -1 */
 197       case GL_COLOR_ATTACHMENT0_EXT:
 198          return BUFFER_COLOR0;
 199       case GL_COLOR_ATTACHMENT1_EXT:
 200          return BUFFER_COLOR1;
 201       case GL_COLOR_ATTACHMENT2_EXT:
 202          return BUFFER_COLOR2;
 203       case GL_COLOR_ATTACHMENT3_EXT:
 204          return BUFFER_COLOR3;
 205       case GL_COLOR_ATTACHMENT4_EXT:
 206          return BUFFER_COLOR4;
 207       case GL_COLOR_ATTACHMENT5_EXT:
 208          return BUFFER_COLOR5;
 209       case GL_COLOR_ATTACHMENT6_EXT:
 210          return BUFFER_COLOR6;
 211       case GL_COLOR_ATTACHMENT7_EXT:
 212          return BUFFER_COLOR7;
 213       default:
 214          /* error */
 215          return -1;
 216    }
 217 }
 218
 219
 220 /**
 221  * Called by glDrawBuffer().
 222  * Specify which renderbuffer(s) to draw into for the first color output.
 223  * <buffer> can name zero, one, two or four renderbuffers!
 224  * \sa _mesa_DrawBuffers
 225  *
 226  * \param buffer  buffer token such as GL_LEFT or GL_FRONT_AND_BACK, etc.
 227  *
 228  * Note that the behaviour of this function depends on whether the
 229  * current ctx->DrawBuffer is a window-system framebuffer (Name=0) or
 230  * a user-created framebuffer object (Name!=0).
 231  *   In the former case, we update the per-context ctx->Color.DrawBuffer
 232  *   state var _and_ the FB's ColorDrawBuffer state.
 233  *   In the later case, we update the FB's ColorDrawBuffer state only.
 234  *
 235  * Furthermore, upon a MakeCurrent() or BindFramebuffer() call, if the
 236  * new FB is a window system FB, we need to re-update the FB's
 237  * ColorDrawBuffer state to match the context.  This is handled in
 238  * _mesa_update_framebuffer().
 239  *
 240  * See the GL_EXT_framebuffer_object spec for more info.
 241  */
 242 void GLAPIENTRY
 243 _mesa_DrawBuffer(GLenum buffer)
 244 {
 245    GLbitfield destMask;
 246    GET_CURRENT_CONTEXT(ctx);
 247    ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx); /* too complex... */
 248
 249    if (MESA_VERBOSE & VERBOSE_API) {
 250       _mesa_debug(ctx, "glDrawBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 251    }
 252
 253    if (buffer == GL_NONE) {
 254       destMask = 0x0;
 255    }
 256    else {
 257       const GLbitfield supportedMask
 258          = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
 259       destMask = draw_buffer_enum_to_bitmask(ctx, buffer);
 260       if (destMask == BAD_MASK) {
 261          /* totally bogus buffer */
 262          _mesa_error(ctx, GL_INVALID_ENUM,
 263                      "glDrawBuffer(buffer=0x%x)", buffer);
 264          return;
 265       }
 266       destMask &= supportedMask;
 267       if (destMask == 0x0) {
 268          /* none of the named color buffers exist! */
 269          _mesa_error(ctx, GL_INVALID_OPERATION,
 270                      "glDrawBuffer(buffer=0x%x)", buffer);
 271          return;
 272       }
 273    }
 274
 275    /* if we get here, there's no error so set new state */
 276    _mesa_drawbuffers(ctx, 1, &buffer, &destMask);
 277
 278    /*
 279     * Call device driver function.
 280     */
 281    if (ctx->Driver.DrawBuffers)
 282       ctx->Driver.DrawBuffers(ctx, 1, &buffer);
 283    else if (ctx->Driver.DrawBuffer)
 284       ctx->Driver.DrawBuffer(ctx, buffer);
 285 }
 286
 287
 288 /**
 289  * Called by glDrawBuffersARB; specifies the destination color renderbuffers
 290  * for N fragment program color outputs.
 291  * \sa _mesa_DrawBuffer
 292  * \param n  number of outputs
 293  * \param buffers  array [n] of renderbuffer names.  Unlike glDrawBuffer, the
 294  *                 names cannot specify more than one buffer.  For example,
 295  *                 GL_FRONT_AND_BACK is illegal.
 296  */
 297 void GLAPIENTRY
 298 _mesa_DrawBuffers(GLsizei n, const GLenum *buffers)
 299 {
 300    GLint output;
 301    GLbitfield usedBufferMask, supportedMask;
 302    GLbitfield destMask[MAX_DRAW_BUFFERS];
 303    GET_CURRENT_CONTEXT(ctx);
 304    ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);
 305
 306    /* Turns out n==0 is a valid input that should not produce an error.
 307     * The remaining code below correctly handles the n==0 case.
 308     *
 309     * From the OpenGL 3.0 specification, page 258:
 310     * "An INVALID_VALUE error is generated if n is greater than
 311     *  MAX_DRAW_BUFFERS."
 312     */
 313    if (n < 0 || n > (GLsizei) ctx->Const.MaxDrawBuffers) {
 314       _mesa_error(ctx, GL_INVALID_VALUE, "glDrawBuffersARB(n)");
 315       return;
 316    }
 317
 318    supportedMask = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
 319    usedBufferMask = 0x0;
 320
 321    /* complicated error checking... */
 322    for (output = 0; output < n; output++) {
 323       if (buffers[output] == GL_NONE) {
 324          destMask[output] = 0x0;
 325       }
 326       else {
 327          /* From the OpenGL 3.0 specification, page 258:
 328           * "If the GL is bound to a framebuffer object and DrawBuffers is
 329           *  supplied with [...] COLOR_ATTACHMENTm where m is greater than or
 330           *  equal to the value of MAX_COLOR_ATTACHMENTS, then the error
 331           *  INVALID_OPERATION results."
 332           */
 333          if (_mesa_is_user_fbo(ctx->DrawBuffer) && buffers[output] >=
 334              GL_COLOR_ATTACHMENT0 + ctx->Const.MaxDrawBuffers) {
 335             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB(buffer)");
 336             return;
 337          }
 338
 339          destMask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
 340
 341          /* From the OpenGL 3.0 specification, page 258:
 342           * "Each buffer listed in bufs must be one of the values from tables
 343           *  4.5 or 4.6.  Otherwise, an INVALID_ENUM error is generated.
 344           */
 345          if (destMask[output] == BAD_MASK) {
 346             _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
 347             return;
 348          }
 349
 350          /* From the OpenGL 3.0 specification, page 259:
 351           * "For both the default framebuffer and framebuffer objects, the
 352           *  constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK are not
 353           *  valid in the bufs array passed to DrawBuffers, and will result in
 354           *  the error INVALID_OPERATION.  This restriction is because these
 355           *  constants may themselves refer to multiple buffers, as shown in
 356           *  table 4.4."
 357           */
 358          if (_mesa_bitcount(destMask[output]) > 1) {
 359             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB(buffer)");
 360             return;
 361          }
 362
 363          /* From the OpenGL 3.0 specification, page 259:
 364           * "If the GL is bound to the default framebuffer and DrawBuffers is
 365           *  supplied with a constant (other than NONE) that does not indicate
 366           *  any of the color buffers allocated to the GL context by the window
 367           *  system, the error INVALID_OPERATION will be generated.
 368           *
 369           *  If the GL is bound to a framebuffer object and DrawBuffers is
 370           *  supplied with a constant from table 4.6 [...] then the error
 371           *  INVALID_OPERATION results."
 372           */
 373          destMask[output] &= supportedMask;
 374          if (destMask[output] == 0) {
 375             _mesa_error(ctx, GL_INVALID_OPERATION,
 376                         "glDrawBuffersARB(unsupported buffer)");
 377             return;
 378          }
 379
 380          /* ES 3.0 is even more restrictive.  From the ES 3.0 spec, page 180:
 381           * "If the GL is bound to a framebuffer object, the ith buffer listed
 382           *  in bufs must be COLOR_ATTACHMENTi or NONE. [...] INVALID_OPERATION."
 383           */
 384          if (_mesa_is_gles3(ctx) && _mesa_is_user_fbo(ctx->DrawBuffer) &&
 385              buffers[output] != GL_NONE &&
 386              buffers[output] != GL_COLOR_ATTACHMENT0 + output) {
 387             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffers(buffer)");
 388             return;
 389          }
 390
 391          /* From the OpenGL 3.0 specification, page 258:
 392           * "Except for NONE, a buffer may not appear more than once in the
 393           *  array pointed to by bufs.  Specifying a buffer more then once will
 394           *  result in the error INVALID_OPERATION."
 395           */
 396          if (destMask[output] & usedBufferMask) {
 397             _mesa_error(ctx, GL_INVALID_OPERATION,
 398                         "glDrawBuffersARB(duplicated buffer)");
 399             return;
 400          }
 401
 402          /* update bitmask */
 403          usedBufferMask |= destMask[output];
 404       }
 405    }
 406
 407    /* OK, if we get here, there were no errors so set the new state */
 408    _mesa_drawbuffers(ctx, n, buffers, destMask);
 409
 410    /*
 411     * Call device driver function.  Note that n can be equal to 0,
 412     * in which case we don't want to reference buffers[0], which
 413     * may not be valid.
 414     */
 415    if (ctx->Driver.DrawBuffers)
 416       ctx->Driver.DrawBuffers(ctx, n, buffers);
 417    else if (ctx->Driver.DrawBuffer)
 418       ctx->Driver.DrawBuffer(ctx, n > 0 ? buffers[0] : GL_NONE);
 419 }
 420
 421
 422 /**
 423  * Performs necessary state updates when _mesa_drawbuffers makes an
 424  * actual change.
 425  */
 426 static void
 427 updated_drawbuffers(struct gl_context *ctx)
 428 {
 429    FLUSH_VERTICES(ctx, _NEW_BUFFERS);
 430
 431    if (ctx->API == API_OPENGL_COMPAT && !ctx->Extensions.ARB_ES2_compatibility) {
 432       struct gl_framebuffer *fb = ctx->DrawBuffer;
 433
 434       /* Flag the FBO as requiring validation. */
 435       if (_mesa_is_user_fbo(fb)) {
 436          fb->_Status = 0;
 437       }
 438    }
 439 }
 440
 441
 442 /**
 443  * Helper function to set the GL_DRAW_BUFFER state in the context and
 444  * current FBO.  Called via glDrawBuffer(), glDrawBuffersARB()
 445  *
 446  * All error checking will have been done prior to calling this function
 447  * so nothing should go wrong at this point.
 448  *
 449  * \param ctx  current context
 450  * \param n    number of color outputs to set
 451  * \param buffers  array[n] of colorbuffer names, like GL_LEFT.
 452  * \param destMask  array[n] of BUFFER_BIT_* bitmasks which correspond to the
 453  *                  colorbuffer names.  (i.e. GL_FRONT_AND_BACK =>
 454  *                  BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT).
 455  */
 456 void
 457 _mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
 458                   const GLbitfield *destMask)
 459 {
 460    struct gl_framebuffer *fb = ctx->DrawBuffer;
 461    GLbitfield mask[MAX_DRAW_BUFFERS];
 462    GLuint buf;
 463
 464    if (!destMask) {
 465       /* compute destMask values now */
 466       const GLbitfield supportedMask = supported_buffer_bitmask(ctx, fb);
 467       GLuint output;
 468       for (output = 0; output < n; output++) {
 469          mask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
 470          ASSERT(mask[output] != BAD_MASK);
 471          mask[output] &= supportedMask;
 472       }
 473       destMask = mask;
 474    }
 475
 476    /*
 477     * If n==1, destMask[0] may have up to four bits set.
 478     * Otherwise, destMask[x] can only have one bit set.
 479     */
 480    if (n == 1) {
 481       GLuint count = 0, destMask0 = destMask[0];
 482       while (destMask0) {
 483          GLint bufIndex = ffs(destMask0) - 1;
 484          if (fb->_ColorDrawBufferIndexes[count] != bufIndex) {
 485             updated_drawbuffers(ctx);
 486             fb->_ColorDrawBufferIndexes[count] = bufIndex;
 487          }
 488          count++;
 489          destMask0 &= ~(1 << bufIndex);
 490       }
 491       fb->ColorDrawBuffer[0] = buffers[0];
 492       fb->_NumColorDrawBuffers = count;
 493    }
 494    else {
 495       GLuint count = 0;
 496       for (buf = 0; buf < n; buf++ ) {
 497          if (destMask[buf]) {
 498             GLint bufIndex = ffs(destMask[buf]) - 1;
 499             /* only one bit should be set in the destMask[buf] field */
 500             ASSERT(_mesa_bitcount(destMask[buf]) == 1);
 501             if (fb->_ColorDrawBufferIndexes[buf] != bufIndex) {
 502                updated_drawbuffers(ctx);
 503                fb->_ColorDrawBufferIndexes[buf] = bufIndex;
 504             }
 505             count = buf + 1;
 506          }
 507          else {
 508             if (fb->_ColorDrawBufferIndexes[buf] != -1) {
 509                updated_drawbuffers(ctx);
 510                fb->_ColorDrawBufferIndexes[buf] = -1;
 511             }
 512          }
 513          fb->ColorDrawBuffer[buf] = buffers[buf];
 514       }
 515       fb->_NumColorDrawBuffers = count;
 516    }
 517
 518    /* set remaining outputs to -1 (GL_NONE) */
 519    for (buf = fb->_NumColorDrawBuffers; buf < ctx->Const.MaxDrawBuffers; buf++) {
 520       if (fb->_ColorDrawBufferIndexes[buf] != -1) {
 521          updated_drawbuffers(ctx);
 522          fb->_ColorDrawBufferIndexes[buf] = -1;
 523       }
 524    }
 525    for (buf = n; buf < ctx->Const.MaxDrawBuffers; buf++) {
 526       fb->ColorDrawBuffer[buf] = GL_NONE;
 527    }
 528
 529    if (_mesa_is_winsys_fbo(fb)) {
 530       /* also set context drawbuffer state */
 531       for (buf = 0; buf < ctx->Const.MaxDrawBuffers; buf++) {
 532          if (ctx->Color.DrawBuffer[buf] != fb->ColorDrawBuffer[buf]) {
 533             updated_drawbuffers(ctx);
 534             ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
 535          }
 536       }
 537    }
 538 }
 539
 540
 541 /**
 542  * Update the current drawbuffer's _ColorDrawBufferIndex[] list, etc.
 543  * from the context's Color.DrawBuffer[] state.
 544  * Use when changing contexts.
 545  */
 546 void
 547 _mesa_update_draw_buffers(struct gl_context *ctx)
 548 {
 549    GLenum buffers[MAX_DRAW_BUFFERS];
 550    GLuint i;
 551
 552    /* should be a window system FBO */
 553    assert(_mesa_is_winsys_fbo(ctx->DrawBuffer));
 554
 555    for (i = 0; i < ctx->Const.MaxDrawBuffers; i++)
 556       buffers[i] = ctx->Color.DrawBuffer[i];
 557
 558    _mesa_drawbuffers(ctx, ctx->Const.MaxDrawBuffers, buffers, NULL);
 559 }
 560
 561
 562 /**
 563  * Like \sa _mesa_drawbuffers(), this is a helper function for setting
 564  * GL_READ_BUFFER state in the context and current FBO.
 565  * \param ctx  the rendering context
 566  * \param buffer  GL_FRONT, GL_BACK, GL_COLOR_ATTACHMENT0, etc.
 567  * \param bufferIndex  the numerical index corresponding to 'buffer'
 568  */
 569 void
 570 _mesa_readbuffer(struct gl_context *ctx, GLenum buffer, GLint bufferIndex)
 571 {
 572    struct gl_framebuffer *fb = ctx->ReadBuffer;
 573
 574    if (_mesa_is_winsys_fbo(fb)) {
 575       /* Only update the per-context READ_BUFFER state if we're bound to
 576        * a window-system framebuffer.
 577        */
 578       ctx->Pixel.ReadBuffer = buffer;
 579    }
 580
 581    fb->ColorReadBuffer = buffer;
 582    fb->_ColorReadBufferIndex = bufferIndex;
 583
 584    ctx->NewState |= _NEW_BUFFERS;
 585 }
 586
 587
 588
 589 /**
 590  * Called by glReadBuffer to set the source renderbuffer for reading pixels.
 591  * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
 592  */
 593 void GLAPIENTRY
 594 _mesa_ReadBuffer(GLenum buffer)
 595 {
 596    struct gl_framebuffer *fb;
 597    GLbitfield supportedMask;
 598    GLint srcBuffer;
 599    GET_CURRENT_CONTEXT(ctx);
 600    ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);
 601
 602    if (MESA_VERBOSE & VERBOSE_API)
 603       _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 604
 605    fb = ctx->ReadBuffer;
 606
 607    if (MESA_VERBOSE & VERBOSE_API)
 608       _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 609
 610    if (buffer == GL_NONE) {
 611       /* This is legal--it means that no buffer should be bound for reading. */
 612       srcBuffer = -1;
 613    }
 614    else {
 615       /* general case / window-system framebuffer */
 616       srcBuffer = read_buffer_enum_to_index(buffer);
 617       if (srcBuffer == -1) {
 618          _mesa_error(ctx, GL_INVALID_ENUM,
 619                      "glReadBuffer(buffer=0x%x)", buffer);
 620          return;
 621       }
 622       supportedMask = supported_buffer_bitmask(ctx, fb);
 623       if (((1 << srcBuffer) & supportedMask) == 0) {
 624          _mesa_error(ctx, GL_INVALID_OPERATION,
 625                      "glReadBuffer(buffer=0x%x)", buffer);
 626          return;
 627       }
 628    }
 629
 630    /* OK, all error checking has been completed now */
 631
 632    _mesa_readbuffer(ctx, buffer, srcBuffer);
 633    ctx->NewState |= _NEW_BUFFERS;
 634
 635    /*
 636     * Call device driver function.
 637     */
 638    if (ctx->Driver.ReadBuffer)
 639       (*ctx->Driver.ReadBuffer)(ctx, buffer);
 640 }