コード例 #1
0
ファイル: buffers.c プロジェクト: VadimGirlin/mesa
/**
 * Called by glReadBuffer to set the source renderbuffer for reading pixels.
 * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
 */
void GLAPIENTRY
_mesa_ReadBuffer(GLenum buffer)
{
   struct gl_framebuffer *fb;
   GLbitfield supportedMask;
   GLint srcBuffer;
   GET_CURRENT_CONTEXT(ctx);
   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);

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

   fb = ctx->ReadBuffer;

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

   if (_mesa_is_user_fbo(fb) && buffer == GL_NONE) {
      /* This is legal for user-created framebuffer objects */
      srcBuffer = -1;
   }
   else {
      /* general case / window-system framebuffer */
      srcBuffer = read_buffer_enum_to_index(buffer);
      if (srcBuffer == -1) {
         _mesa_error(ctx, GL_INVALID_ENUM,
                     "glReadBuffer(buffer=0x%x)", buffer);
         return;
      }
      supportedMask = supported_buffer_bitmask(ctx, fb);
      if (((1 << srcBuffer) & supportedMask) == 0) {
         _mesa_error(ctx, GL_INVALID_OPERATION,
                     "glReadBuffer(buffer=0x%x)", buffer);
         return;
      }
   }

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

   _mesa_readbuffer(ctx, buffer, srcBuffer);
   ctx->NewState |= _NEW_BUFFERS;

   /*
    * Call device driver function.
    */
   if (ctx->Driver.ReadBuffer)
      (*ctx->Driver.ReadBuffer)(ctx, buffer);
}
コード例 #2
0
/**
 * Called by glReadBuffer to set the source renderbuffer for reading pixels.
 * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
 */
void GLAPIENTRY
_mesa_ReadBuffer(GLenum buffer)
{
   struct gl_framebuffer *fb;
   GLbitfield supportedMask;
   GLint srcBuffer;
   GET_CURRENT_CONTEXT(ctx);

   FLUSH_VERTICES(ctx, 0);

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

   fb = ctx->ReadBuffer;

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

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

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

   _mesa_readbuffer(ctx, buffer, srcBuffer);

   /*
    * Call device driver function.
    */
   if (ctx->Driver.ReadBuffer)
      (*ctx->Driver.ReadBuffer)(ctx, buffer);
}
コード例 #3
0
/**
 * Called by glDrawBuffer().
 * Specify which renderbuffer(s) to draw into for the first color output.
 * <buffer> can name zero, one, two or four renderbuffers!
 * \sa _mesa_DrawBuffers
 *
 * \param buffer  buffer token such as GL_LEFT or GL_FRONT_AND_BACK, etc.
 *
 * Note that the behaviour of this function depends on whether the
 * current ctx->DrawBuffer is a window-system framebuffer or a user-created
 * framebuffer object.
 *   In the former case, we update the per-context ctx->Color.DrawBuffer
 *   state var _and_ the FB's ColorDrawBuffer state.
 *   In the later case, we update the FB's ColorDrawBuffer state only.
 *
 * Furthermore, upon a MakeCurrent() or BindFramebuffer() call, if the
 * new FB is a window system FB, we need to re-update the FB's
 * ColorDrawBuffer state to match the context.  This is handled in
 * _mesa_update_framebuffer().
 *
 * See the GL_EXT_framebuffer_object spec for more info.
 */
void GLAPIENTRY
_mesa_DrawBuffer(GLenum buffer)
{
   GLbitfield destMask;
   GET_CURRENT_CONTEXT(ctx);

   FLUSH_VERTICES(ctx, 0);

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

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

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

   /*
    * Call device driver function.
    */
   if (ctx->Driver.DrawBuffers)
      ctx->Driver.DrawBuffers(ctx, 1, &buffer);
   else if (ctx->Driver.DrawBuffer)
      ctx->Driver.DrawBuffer(ctx, buffer);
}
コード例 #4
0
ファイル: buffers.c プロジェクト: dumbbell/mesa
/**
 * Called by glDrawBuffer().
 * Specify which renderbuffer(s) to draw into for the first color output.
 * <buffer> can name zero, one, two or four renderbuffers!
 * \sa _mesa_DrawBuffers
 *
 * \param buffer  buffer token such as GL_LEFT or GL_FRONT_AND_BACK, etc.
 *
 * Note that the behaviour of this function depends on whether the
 * current ctx->DrawBuffer is a window-system framebuffer or a user-created
 * framebuffer object.
 *   In the former case, we update the per-context ctx->Color.DrawBuffer
 *   state var _and_ the FB's ColorDrawBuffer state.
 *   In the later case, we update the FB's ColorDrawBuffer state only.
 *
 * Furthermore, upon a MakeCurrent() or BindFramebuffer() call, if the
 * new FB is a window system FB, we need to re-update the FB's
 * ColorDrawBuffer state to match the context.  This is handled in
 * _mesa_update_framebuffer().
 *
 * See the GL_EXT_framebuffer_object spec for more info.
 */
void
_mesa_draw_buffer(struct gl_context *ctx, struct gl_framebuffer *fb,
                  GLenum buffer, const char *caller)
{
   GLbitfield destMask;

   FLUSH_VERTICES(ctx, 0);

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

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

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

   /* Call device driver function only if fb is the bound draw buffer */
   if (fb == ctx->DrawBuffer) {
      if (ctx->Driver.DrawBuffers)
         ctx->Driver.DrawBuffers(ctx, 1, &buffer);
      else if (ctx->Driver.DrawBuffer)
         ctx->Driver.DrawBuffer(ctx, buffer);
   }
}
コード例 #5
0
ファイル: buffers.c プロジェクト: dumbbell/mesa
/**
 * Called by glReadBuffer to set the source renderbuffer for reading pixels.
 * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
 */
void
_mesa_read_buffer(struct gl_context *ctx, struct gl_framebuffer *fb,
                  GLenum buffer, const char *caller)
{
   GLbitfield supportedMask;
   GLint srcBuffer;

   FLUSH_VERTICES(ctx, 0);

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

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

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

   _mesa_readbuffer(ctx, fb, buffer, srcBuffer);

   /* Call the device driver function only if fb is the bound read buffer */
   if (fb == ctx->ReadBuffer) {
      if (ctx->Driver.ReadBuffer)
         (*ctx->Driver.ReadBuffer)(ctx, buffer);
   }
}
コード例 #6
0
/**
 * Helper function to set the GL_DRAW_BUFFER state in the context and
 * current FBO.  Called via glDrawBuffer(), glDrawBuffersARB()
 *
 * All error checking will have been done prior to calling this function
 * so nothing should go wrong at this point.
 *
 * \param ctx  current context
 * \param n    number of color outputs to set
 * \param buffers  array[n] of colorbuffer names, like GL_LEFT.
 * \param destMask  array[n] of BUFFER_BIT_* bitmasks which correspond to the
 *                  colorbuffer names.  (i.e. GL_FRONT_AND_BACK =>
 *                  BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT).
 */
void
_mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
                  const GLbitfield *destMask)
{
   struct gl_framebuffer *fb = ctx->DrawBuffer;
   GLbitfield mask[MAX_DRAW_BUFFERS];
   GLuint buf;

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

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

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

   if (_mesa_is_winsys_fbo(fb)) {
      /* also set context drawbuffer state */
      for (buf = 0; buf < ctx->Const.MaxDrawBuffers; buf++) {
         if (ctx->Color.DrawBuffer[buf] != fb->ColorDrawBuffer[buf]) {
	    updated_drawbuffers(ctx);
            ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
         }
      }
   }
}
コード例 #7
0
/**
 * Called by glDrawBuffersARB; specifies the destination color renderbuffers
 * for N fragment program color outputs.
 * \sa _mesa_DrawBuffer
 * \param n  number of outputs
 * \param buffers  array [n] of renderbuffer names.  Unlike glDrawBuffer, the
 *                 names cannot specify more than one buffer.  For example,
 *                 GL_FRONT_AND_BACK is illegal.
 */
void GLAPIENTRY
_mesa_DrawBuffers(GLsizei n, const GLenum *buffers)
{
   GLint output;
   GLbitfield usedBufferMask, supportedMask;
   GLbitfield destMask[MAX_DRAW_BUFFERS];
   GET_CURRENT_CONTEXT(ctx);

   FLUSH_VERTICES(ctx, 0);

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

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

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

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

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

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

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

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

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

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

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

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

   /*
    * Call device driver function.  Note that n can be equal to 0,
    * in which case we don't want to reference buffers[0], which
    * may not be valid.
    */
   if (ctx->Driver.DrawBuffers)
      ctx->Driver.DrawBuffers(ctx, n, buffers);
   else if (ctx->Driver.DrawBuffer)
      ctx->Driver.DrawBuffer(ctx, n > 0 ? buffers[0] : GL_NONE);
}
コード例 #8
0
ファイル: buffers.c プロジェクト: VadimGirlin/mesa
/**
 * Called by glDrawBuffersARB; specifies the destination color renderbuffers
 * for N fragment program color outputs.
 * \sa _mesa_DrawBuffer
 * \param n  number of outputs
 * \param buffers  array [n] of renderbuffer names.  Unlike glDrawBuffer, the
 *                 names cannot specify more than one buffer.  For example,
 *                 GL_FRONT_AND_BACK is illegal.
 */
void GLAPIENTRY
_mesa_DrawBuffers(GLsizei n, const GLenum *buffers)
{
   GLint output;
   GLbitfield usedBufferMask, supportedMask;
   GLbitfield destMask[MAX_DRAW_BUFFERS];
   GET_CURRENT_CONTEXT(ctx);
   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);

   /* Turns out n==0 is a valid input that should not produce an error.
    * The remaining code below correctly handles the n==0 case.
    */
   if (n < 0 || n > (GLsizei) ctx->Const.MaxDrawBuffers) {
      _mesa_error(ctx, GL_INVALID_VALUE, "glDrawBuffersARB(n)");
      return;
   }

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

   /* complicated error checking... */
   for (output = 0; output < n; output++) {
      if (buffers[output] == GL_NONE) {
         destMask[output] = 0x0;
      }
      else {
         destMask[output] = draw_buffer_enum_to_bitmask(buffers[output]);
         if (destMask[output] == BAD_MASK
             || _mesa_bitcount(destMask[output]) > 1) {
            _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
            return;
         }         
         destMask[output] &= supportedMask;
         if (destMask[output] == 0) {
            _mesa_error(ctx, GL_INVALID_OPERATION,
                        "glDrawBuffersARB(unsupported buffer)");
            return;
         }
         if (destMask[output] & usedBufferMask) {
            /* can't specify a dest buffer more than once! */
            _mesa_error(ctx, GL_INVALID_OPERATION,
                        "glDrawBuffersARB(duplicated buffer)");
            return;
         }

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

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

   /*
    * Call device driver function.  Note that n can be equal to 0,
    * in which case we don't want to reference buffers[0], which
    * may not be valid.
    */
   if (ctx->Driver.DrawBuffers)
      ctx->Driver.DrawBuffers(ctx, n, buffers);
   else if (ctx->Driver.DrawBuffer)
      ctx->Driver.DrawBuffer(ctx, n > 0 ? buffers[0] : GL_NONE);
}
コード例 #9
0
ファイル: buffers.c プロジェクト: AchironOS/chromium.src
/**
 * Helper function to set the GL_DRAW_BUFFER state in the context and
 * current FBO.  Called via glDrawBuffer(), glDrawBuffersARB()
 *
 * All error checking will have been done prior to calling this function
 * so nothing should go wrong at this point.
 *
 * \param ctx  current context
 * \param n    number of color outputs to set
 * \param buffers  array[n] of colorbuffer names, like GL_LEFT.
 * \param destMask  array[n] of BUFFER_BIT_* bitmasks which correspond to the
 *                  colorbuffer names.  (i.e. GL_FRONT_AND_BACK =>
 *                  BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT).
 */
void
_mesa_drawbuffers(GLcontext *ctx, GLuint n, const GLenum *buffers,
                  const GLbitfield *destMask)
{
   struct gl_framebuffer *fb = ctx->DrawBuffer;
   GLbitfield mask[MAX_DRAW_BUFFERS];
   GLboolean newState = GL_FALSE;

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

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

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

   if (newState)
      FLUSH_VERTICES(ctx, _NEW_BUFFERS);
}