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_gles3(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             if (ctx->DrawBuffer->Visual.doubleBufferMode)
 116                return BUFFER_BIT_BACK_LEFT;
 117             return BUFFER_BIT_FRONT_LEFT;
 118          }
 119          return BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
 120       case GL_RIGHT:
 121          return BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
 122       case GL_FRONT_RIGHT:
 123          return BUFFER_BIT_FRONT_RIGHT;
 124       case GL_BACK_RIGHT:
 125          return BUFFER_BIT_BACK_RIGHT;
 126       case GL_BACK_LEFT:
 127          return BUFFER_BIT_BACK_LEFT;
 128       case GL_FRONT_AND_BACK:
 129          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT
 130               | BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
 131       case GL_LEFT:
 132          return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT;
 133       case GL_FRONT_LEFT:
 134          return BUFFER_BIT_FRONT_LEFT;
 135       case GL_AUX0:
 136          return BUFFER_BIT_AUX0;
 137       case GL_AUX1:
 138       case GL_AUX2:
 139       case GL_AUX3:
 140          return 1 << BUFFER_COUNT; /* invalid, but not BAD_MASK */
 141       case GL_COLOR_ATTACHMENT0_EXT:
 142          return BUFFER_BIT_COLOR0;
 143       case GL_COLOR_ATTACHMENT1_EXT:
 144          return BUFFER_BIT_COLOR1;
 145       case GL_COLOR_ATTACHMENT2_EXT:
 146          return BUFFER_BIT_COLOR2;
 147       case GL_COLOR_ATTACHMENT3_EXT:
 148          return BUFFER_BIT_COLOR3;
 149       case GL_COLOR_ATTACHMENT4_EXT:
 150          return BUFFER_BIT_COLOR4;
 151       case GL_COLOR_ATTACHMENT5_EXT:
 152          return BUFFER_BIT_COLOR5;
 153       case GL_COLOR_ATTACHMENT6_EXT:
 154          return BUFFER_BIT_COLOR6;
 155       case GL_COLOR_ATTACHMENT7_EXT:
 156          return BUFFER_BIT_COLOR7;
 157       default:
 158          /* error */
 159          return BAD_MASK;
 160    }
 161 }
 162
 163
 164 /**
 165  * Helper routine used by glReadBuffer.
 166  * Given a GLenum naming a color buffer, return the index of the corresponding
 167  * renderbuffer (a BUFFER_* value).
 168  * return -1 for an invalid buffer.
 169  */
 170 static GLint
 171 read_buffer_enum_to_index(GLenum buffer)
 172 {
 173    switch (buffer) {
 174       case GL_FRONT:
 175          return BUFFER_FRONT_LEFT;
 176       case GL_BACK:
 177          return BUFFER_BACK_LEFT;
 178       case GL_RIGHT:
 179          return BUFFER_FRONT_RIGHT;
 180       case GL_FRONT_RIGHT:
 181          return BUFFER_FRONT_RIGHT;
 182       case GL_BACK_RIGHT:
 183          return BUFFER_BACK_RIGHT;
 184       case GL_BACK_LEFT:
 185          return BUFFER_BACK_LEFT;
 186       case GL_LEFT:
 187          return BUFFER_FRONT_LEFT;
 188       case GL_FRONT_LEFT:
 189          return BUFFER_FRONT_LEFT;
 190       case GL_AUX0:
 191          return BUFFER_AUX0;
 192       case GL_AUX1:
 193       case GL_AUX2:
 194       case GL_AUX3:
 195          return BUFFER_COUNT; /* invalid, but not -1 */
 196       case GL_COLOR_ATTACHMENT0_EXT:
 197          return BUFFER_COLOR0;
 198       case GL_COLOR_ATTACHMENT1_EXT:
 199          return BUFFER_COLOR1;
 200       case GL_COLOR_ATTACHMENT2_EXT:
 201          return BUFFER_COLOR2;
 202       case GL_COLOR_ATTACHMENT3_EXT:
 203          return BUFFER_COLOR3;
 204       case GL_COLOR_ATTACHMENT4_EXT:
 205          return BUFFER_COLOR4;
 206       case GL_COLOR_ATTACHMENT5_EXT:
 207          return BUFFER_COLOR5;
 208       case GL_COLOR_ATTACHMENT6_EXT:
 209          return BUFFER_COLOR6;
 210       case GL_COLOR_ATTACHMENT7_EXT:
 211          return BUFFER_COLOR7;
 212       default:
 213          /* error */
 214          return -1;
 215    }
 216 }
 217
 218
 219 /**
 220  * Called by glDrawBuffer().
 221  * Specify which renderbuffer(s) to draw into for the first color output.
 222  * <buffer> can name zero, one, two or four renderbuffers!
 223  * \sa _mesa_DrawBuffers
 224  *
 225  * \param buffer  buffer token such as GL_LEFT or GL_FRONT_AND_BACK, etc.
 226  *
 227  * Note that the behaviour of this function depends on whether the
 228  * current ctx->DrawBuffer is a window-system framebuffer or a user-created
 229  * framebuffer object.
 230  *   In the former case, we update the per-context ctx->Color.DrawBuffer
 231  *   state var _and_ the FB's ColorDrawBuffer state.
 232  *   In the later case, we update the FB's ColorDrawBuffer state only.
 233  *
 234  * Furthermore, upon a MakeCurrent() or BindFramebuffer() call, if the
 235  * new FB is a window system FB, we need to re-update the FB's
 236  * ColorDrawBuffer state to match the context.  This is handled in
 237  * _mesa_update_framebuffer().
 238  *
 239  * See the GL_EXT_framebuffer_object spec for more info.
 240  */
 241 void GLAPIENTRY
 242 _mesa_DrawBuffer(GLenum buffer)
 243 {
 244    GLbitfield destMask;
 245    GET_CURRENT_CONTEXT(ctx);
 246
 247    FLUSH_VERTICES(ctx, 0);
 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
 305    FLUSH_VERTICES(ctx, 0);
 306
 307    /* Turns out n==0 is a valid input that should not produce an error.
 308     * The remaining code below correctly handles the n==0 case.
 309     *
 310     * From the OpenGL 3.0 specification, page 258:
 311     * "An INVALID_VALUE error is generated if n is greater than
 312     *  MAX_DRAW_BUFFERS."
 313     */
 314    if (n < 0 || n > (GLsizei) ctx->Const.MaxDrawBuffers) {
 315       _mesa_error(ctx, GL_INVALID_VALUE, "glDrawBuffersARB(n)");
 316       return;
 317    }
 318
 319    supportedMask = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
 320    usedBufferMask = 0x0;
 321
 322    /* From the ES 3.0 specification, page 180:
 323     * "If the GL is bound to the default framebuffer, then n must be 1
 324     *  and the constant must be BACK or NONE."
 325     */
 326    if (_mesa_is_gles3(ctx) && _mesa_is_winsys_fbo(ctx->DrawBuffer) &&
 327        (n != 1 || (buffers[0] != GL_NONE && buffers[0] != GL_BACK))) {
 328       _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffers(buffer)");
 329       return;
 330    }
 331
 332    /* complicated error checking... */
 333    for (output = 0; output < n; output++) {
 334       if (buffers[output] == GL_NONE) {
 335          destMask[output] = 0x0;
 336       }
 337       else {
 338          /* Page 259 (page 275 of the PDF) in section 4.2.1 of the OpenGL 3.0
 339           * spec (20080923) says:
 340           *
 341           *     "If the GL is bound to a framebuffer object and DrawBuffers is
 342           *     supplied with [...] COLOR_ATTACHMENTm where m is greater than
 343           *     or equal to the value of MAX_COLOR_ATTACHMENTS, then the error
 344           *     INVALID_OPERATION results."
 345           */
 346          if (_mesa_is_user_fbo(ctx->DrawBuffer) && buffers[output] >=
 347              GL_COLOR_ATTACHMENT0 + ctx->Const.MaxDrawBuffers) {
 348             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB(buffer)");
 349             return;
 350          }
 351
 352          destMask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
 353
 354          /* From the OpenGL 3.0 specification, page 258:
 355           * "Each buffer listed in bufs must be one of the values from tables
 356           *  4.5 or 4.6.  Otherwise, an INVALID_ENUM error is generated.
 357           */
 358          if (destMask[output] == BAD_MASK) {
 359             _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
 360             return;
 361          }
 362
 363          /* From the OpenGL 3.0 specification, page 259:
 364           * "For both the default framebuffer and framebuffer objects, the
 365           *  constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK are not
 366           *  valid in the bufs array passed to DrawBuffers, and will result in
 367           *  the error INVALID_OPERATION.  This restriction is because these
 368           *  constants may themselves refer to multiple buffers, as shown in
 369           *  table 4.4."
 370           */
 371          if (_mesa_bitcount(destMask[output]) > 1) {
 372             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB(buffer)");
 373             return;
 374          }
 375
 376          /* From the OpenGL 3.0 specification, page 259:
 377           * "If the GL is bound to the default framebuffer and DrawBuffers is
 378           *  supplied with a constant (other than NONE) that does not indicate
 379           *  any of the color buffers allocated to the GL context by the window
 380           *  system, the error INVALID_OPERATION will be generated.
 381           *
 382           *  If the GL is bound to a framebuffer object and DrawBuffers is
 383           *  supplied with a constant from table 4.6 [...] then the error
 384           *  INVALID_OPERATION results."
 385           */
 386          destMask[output] &= supportedMask;
 387          if (destMask[output] == 0) {
 388             _mesa_error(ctx, GL_INVALID_OPERATION,
 389                         "glDrawBuffersARB(unsupported buffer)");
 390             return;
 391          }
 392
 393          /* ES 3.0 is even more restrictive.  From the ES 3.0 spec, page 180:
 394           * "If the GL is bound to a framebuffer object, the ith buffer listed
 395           *  in bufs must be COLOR_ATTACHMENTi or NONE. [...] INVALID_OPERATION."
 396           */
 397          if (_mesa_is_gles3(ctx) && _mesa_is_user_fbo(ctx->DrawBuffer) &&
 398              buffers[output] != GL_NONE &&
 399              buffers[output] != GL_COLOR_ATTACHMENT0 + output) {
 400             _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffers(buffer)");
 401             return;
 402          }
 403
 404          /* From the OpenGL 3.0 specification, page 258:
 405           * "Except for NONE, a buffer may not appear more than once in the
 406           *  array pointed to by bufs.  Specifying a buffer more then once will
 407           *  result in the error INVALID_OPERATION."
 408           */
 409          if (destMask[output] & usedBufferMask) {
 410             _mesa_error(ctx, GL_INVALID_OPERATION,
 411                         "glDrawBuffersARB(duplicated buffer)");
 412             return;
 413          }
 414
 415          /* update bitmask */
 416          usedBufferMask |= destMask[output];
 417       }
 418    }
 419
 420    /* OK, if we get here, there were no errors so set the new state */
 421    _mesa_drawbuffers(ctx, n, buffers, destMask);
 422
 423    /*
 424     * Call device driver function.  Note that n can be equal to 0,
 425     * in which case we don't want to reference buffers[0], which
 426     * may not be valid.
 427     */
 428    if (ctx->Driver.DrawBuffers)
 429       ctx->Driver.DrawBuffers(ctx, n, buffers);
 430    else if (ctx->Driver.DrawBuffer)
 431       ctx->Driver.DrawBuffer(ctx, n > 0 ? buffers[0] : GL_NONE);
 432 }
 433
 434
 435 /**
 436  * Performs necessary state updates when _mesa_drawbuffers makes an
 437  * actual change.
 438  */
 439 static void
 440 updated_drawbuffers(struct gl_context *ctx)
 441 {
 442    FLUSH_VERTICES(ctx, _NEW_BUFFERS);
 443
 444    if (ctx->API == API_OPENGL_COMPAT && !ctx->Extensions.ARB_ES2_compatibility) {
 445       struct gl_framebuffer *fb = ctx->DrawBuffer;
 446
 447       /* Flag the FBO as requiring validation. */
 448       if (_mesa_is_user_fbo(fb)) {
 449          fb->_Status = 0;
 450       }
 451    }
 452 }
 453
 454
 455 /**
 456  * Helper function to set the GL_DRAW_BUFFER state in the context and
 457  * current FBO.  Called via glDrawBuffer(), glDrawBuffersARB()
 458  *
 459  * All error checking will have been done prior to calling this function
 460  * so nothing should go wrong at this point.
 461  *
 462  * \param ctx  current context
 463  * \param n    number of color outputs to set
 464  * \param buffers  array[n] of colorbuffer names, like GL_LEFT.
 465  * \param destMask  array[n] of BUFFER_BIT_* bitmasks which correspond to the
 466  *                  colorbuffer names.  (i.e. GL_FRONT_AND_BACK =>
 467  *                  BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT).
 468  */
 469 void
 470 _mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
 471                   const GLbitfield *destMask)
 472 {
 473    struct gl_framebuffer *fb = ctx->DrawBuffer;
 474    GLbitfield mask[MAX_DRAW_BUFFERS];
 475    GLuint buf;
 476
 477    if (!destMask) {
 478       /* compute destMask values now */
 479       const GLbitfield supportedMask = supported_buffer_bitmask(ctx, fb);
 480       GLuint output;
 481       for (output = 0; output < n; output++) {
 482          mask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
 483          ASSERT(mask[output] != BAD_MASK);
 484          mask[output] &= supportedMask;
 485       }
 486       destMask = mask;
 487    }
 488
 489    /*
 490     * If n==1, destMask[0] may have up to four bits set.
 491     * Otherwise, destMask[x] can only have one bit set.
 492     */
 493    if (n == 1) {
 494       GLuint count = 0, destMask0 = destMask[0];
 495       while (destMask0) {
 496          GLint bufIndex = ffs(destMask0) - 1;
 497          if (fb->_ColorDrawBufferIndexes[count] != bufIndex) {
 498             updated_drawbuffers(ctx);
 499             fb->_ColorDrawBufferIndexes[count] = bufIndex;
 500          }
 501          count++;
 502          destMask0 &= ~(1 << bufIndex);
 503       }
 504       fb->ColorDrawBuffer[0] = buffers[0];
 505       fb->_NumColorDrawBuffers = count;
 506    }
 507    else {
 508       GLuint count = 0;
 509       for (buf = 0; buf < n; buf++ ) {
 510          if (destMask[buf]) {
 511             GLint bufIndex = ffs(destMask[buf]) - 1;
 512             /* only one bit should be set in the destMask[buf] field */
 513             ASSERT(_mesa_bitcount(destMask[buf]) == 1);
 514             if (fb->_ColorDrawBufferIndexes[buf] != bufIndex) {
 515                updated_drawbuffers(ctx);
 516                fb->_ColorDrawBufferIndexes[buf] = bufIndex;
 517             }
 518             count = buf + 1;
 519          }
 520          else {
 521             if (fb->_ColorDrawBufferIndexes[buf] != -1) {
 522                updated_drawbuffers(ctx);
 523                fb->_ColorDrawBufferIndexes[buf] = -1;
 524             }
 525          }
 526          fb->ColorDrawBuffer[buf] = buffers[buf];
 527       }
 528       fb->_NumColorDrawBuffers = count;
 529    }
 530
 531    /* set remaining outputs to -1 (GL_NONE) */
 532    for (buf = fb->_NumColorDrawBuffers; buf < ctx->Const.MaxDrawBuffers; buf++) {
 533       if (fb->_ColorDrawBufferIndexes[buf] != -1) {
 534          updated_drawbuffers(ctx);
 535          fb->_ColorDrawBufferIndexes[buf] = -1;
 536       }
 537    }
 538    for (buf = n; buf < ctx->Const.MaxDrawBuffers; buf++) {
 539       fb->ColorDrawBuffer[buf] = GL_NONE;
 540    }
 541
 542    if (_mesa_is_winsys_fbo(fb)) {
 543       /* also set context drawbuffer state */
 544       for (buf = 0; buf < ctx->Const.MaxDrawBuffers; buf++) {
 545          if (ctx->Color.DrawBuffer[buf] != fb->ColorDrawBuffer[buf]) {
 546             updated_drawbuffers(ctx);
 547             ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
 548          }
 549       }
 550    }
 551 }
 552
 553
 554 /**
 555  * Update the current drawbuffer's _ColorDrawBufferIndex[] list, etc.
 556  * from the context's Color.DrawBuffer[] state.
 557  * Use when changing contexts.
 558  */
 559 void
 560 _mesa_update_draw_buffers(struct gl_context *ctx)
 561 {
 562    GLenum buffers[MAX_DRAW_BUFFERS];
 563    GLuint i;
 564
 565    /* should be a window system FBO */
 566    assert(_mesa_is_winsys_fbo(ctx->DrawBuffer));
 567
 568    for (i = 0; i < ctx->Const.MaxDrawBuffers; i++)
 569       buffers[i] = ctx->Color.DrawBuffer[i];
 570
 571    _mesa_drawbuffers(ctx, ctx->Const.MaxDrawBuffers, buffers, NULL);
 572 }
 573
 574
 575 /**
 576  * Like \sa _mesa_drawbuffers(), this is a helper function for setting
 577  * GL_READ_BUFFER state in the context and current FBO.
 578  * \param ctx  the rendering context
 579  * \param buffer  GL_FRONT, GL_BACK, GL_COLOR_ATTACHMENT0, etc.
 580  * \param bufferIndex  the numerical index corresponding to 'buffer'
 581  */
 582 void
 583 _mesa_readbuffer(struct gl_context *ctx, GLenum buffer, GLint bufferIndex)
 584 {
 585    struct gl_framebuffer *fb = ctx->ReadBuffer;
 586
 587    if (_mesa_is_winsys_fbo(fb)) {
 588       /* Only update the per-context READ_BUFFER state if we're bound to
 589        * a window-system framebuffer.
 590        */
 591       ctx->Pixel.ReadBuffer = buffer;
 592    }
 593
 594    fb->ColorReadBuffer = buffer;
 595    fb->_ColorReadBufferIndex = bufferIndex;
 596
 597    ctx->NewState |= _NEW_BUFFERS;
 598 }
 599
 600
 601
 602 /**
 603  * Called by glReadBuffer to set the source renderbuffer for reading pixels.
 604  * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
 605  */
 606 void GLAPIENTRY
 607 _mesa_ReadBuffer(GLenum buffer)
 608 {
 609    struct gl_framebuffer *fb;
 610    GLbitfield supportedMask;
 611    GLint srcBuffer;
 612    GET_CURRENT_CONTEXT(ctx);
 613
 614    FLUSH_VERTICES(ctx, 0);
 615
 616    if (MESA_VERBOSE & VERBOSE_API)
 617       _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 618
 619    fb = ctx->ReadBuffer;
 620
 621    if (MESA_VERBOSE & VERBOSE_API)
 622       _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 623
 624    if (buffer == GL_NONE) {
 625       /* This is legal--it means that no buffer should be bound for reading. */
 626       srcBuffer = -1;
 627    }
 628    else {
 629       /* general case / window-system framebuffer */
 630       srcBuffer = read_buffer_enum_to_index(buffer);
 631       if (srcBuffer == -1) {
 632          _mesa_error(ctx, GL_INVALID_ENUM,
 633                      "glReadBuffer(buffer=0x%x)", buffer);
 634          return;
 635       }
 636       supportedMask = supported_buffer_bitmask(ctx, fb);
 637       if (((1 << srcBuffer) & supportedMask) == 0) {
 638          _mesa_error(ctx, GL_INVALID_OPERATION,
 639                      "glReadBuffer(buffer=0x%x)", buffer);
 640          return;
 641       }
 642    }
 643
 644    /* OK, all error checking has been completed now */
 645
 646    _mesa_readbuffer(ctx, buffer, srcBuffer);
 647
 648    /*
 649     * Call device driver function.
 650     */
 651    if (ctx->Driver.ReadBuffer)
 652       (*ctx->Driver.ReadBuffer)(ctx, buffer);
 653 }