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