X-Git-Url: https://git.libre-soc.org/?a=blobdiff_plain;f=src%2Fmesa%2Fmain%2Fbuffers.c;h=b23d2f612bfdef278fcfb6818fcffb34ef160e01;hb=08d90fe8a5e12d92994c05b2ec9f68ab7232275c;hp=f7280e40cceb44c5aa929cbe7142364167feaa3d;hpb=961b7cad05d525850cb8f25147f847b0291f3046;p=mesa.git

diff --git a/src/mesa/main/buffers.c b/src/mesa/main/buffers.c
index f7280e40cce..b23d2f612bf 100644
--- a/src/mesa/main/buffers.c
+++ b/src/mesa/main/buffers.c
@@ -1,10 +1,8 @@
-/* $Id: buffers.c,v 1.26 2001/01/29 22:10:37 brianp Exp $ */
-
 /*
  * Mesa 3-D graphics library
- * Version:  3.5
+ * Version:  7.1
  *
- * Copyright (C) 1999-2001  Brian Paul   All Rights Reserved.
+ * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -25,348 +23,481 @@
  */
 
 
-#ifdef PC_HEADER
-#include "all.h"
-#else
+/**
+ * \file buffers.c
+ * glReadBuffer, DrawBuffer functions.
+ */
+
+
+
 #include "glheader.h"
-#include "accum.h"
 #include "buffers.h"
 #include "colormac.h"
 #include "context.h"
-#include "depth.h"
 #include "enums.h"
-#include "macros.h"
-#include "masking.h"
-#include "mem.h"
-#include "stencil.h"
+#include "fbobject.h"
 #include "state.h"
-#include "mtypes.h"
-#endif
 
 
+#define BAD_MASK ~0u
 
-void
-_mesa_ClearIndex( GLfloat c )
-{
-   GET_CURRENT_CONTEXT(ctx);
-   ASSERT_OUTSIDE_BEGIN_END(ctx);
 
-   if (ctx->Color.ClearIndex == (GLuint) c)
-      return;
-   
-   FLUSH_VERTICES(ctx, _NEW_COLOR);
-   ctx->Color.ClearIndex = (GLuint) c;
+/**
+ * Return bitmask of BUFFER_BIT_* flags indicating which color buffers are
+ * available to the rendering context (for drawing or reading).
+ * This depends on the type of framebuffer.  For window system framebuffers
+ * we look at the framebuffer's visual.  But for user-create framebuffers we
+ * look at the number of supported color attachments.
+ * \param fb  the framebuffer to draw to, or read from
+ * \return  bitmask of BUFFER_BIT_* flags
+ */
+static GLbitfield
+supported_buffer_bitmask(const GLcontext *ctx, const struct gl_framebuffer *fb)
+{
+   GLbitfield mask = 0x0;
+
+   if (fb->Name > 0) {
+      /* A user-created renderbuffer */
+      GLuint i;
+      ASSERT(ctx->Extensions.EXT_framebuffer_object);
+      for (i = 0; i < ctx->Const.MaxColorAttachments; i++) {
+         mask |= (BUFFER_BIT_COLOR0 << i);
+      }
+   }
+   else {
+      /* A window system framebuffer */
+      GLint i;
+      mask = BUFFER_BIT_FRONT_LEFT; /* always have this */
+      if (fb->Visual.stereoMode) {
+         mask |= BUFFER_BIT_FRONT_RIGHT;
+         if (fb->Visual.doubleBufferMode) {
+            mask |= BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
+         }
+      }
+      else if (fb->Visual.doubleBufferMode) {
+         mask |= BUFFER_BIT_BACK_LEFT;
+      }
 
-   if (!ctx->Visual.rgbMode && ctx->Driver.ClearIndex) {
-      /* it's OK to call glClearIndex in RGBA mode but it should be a NOP */
-      (*ctx->Driver.ClearIndex)( ctx, ctx->Color.ClearIndex );
+      for (i = 0; i < fb->Visual.numAuxBuffers; i++) {
+         mask |= (BUFFER_BIT_AUX0 << i);
+      }
    }
-}
 
+   return mask;
+}
 
 
-void
-_mesa_ClearColor( GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha )
+/**
+ * Helper routine used by glDrawBuffer and glDrawBuffersARB.
+ * Given a GLenum naming one or more color buffers (such as
+ * GL_FRONT_AND_BACK), return the corresponding bitmask of BUFFER_BIT_* flags.
+ */
+static GLbitfield
+draw_buffer_enum_to_bitmask(GLenum buffer)
 {
-   GLchan tmp[4];
-   GET_CURRENT_CONTEXT(ctx);
-   ASSERT_OUTSIDE_BEGIN_END(ctx);
-
-   UNCLAMPED_FLOAT_TO_CHAN(tmp[0], red);
-   UNCLAMPED_FLOAT_TO_CHAN(tmp[1], green);
-   UNCLAMPED_FLOAT_TO_CHAN(tmp[2], blue);
-   UNCLAMPED_FLOAT_TO_CHAN(tmp[3], alpha);
-
-   if (TEST_EQ_4V(tmp, ctx->Color.ClearColor))
-      return;
+   switch (buffer) {
+      case GL_NONE:
+         return 0;
+      case GL_FRONT:
+         return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_FRONT_RIGHT;
+      case GL_BACK:
+         return BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
+      case GL_RIGHT:
+         return BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
+      case GL_FRONT_RIGHT:
+         return BUFFER_BIT_FRONT_RIGHT;
+      case GL_BACK_RIGHT:
+         return BUFFER_BIT_BACK_RIGHT;
+      case GL_BACK_LEFT:
+         return BUFFER_BIT_BACK_LEFT;
+      case GL_FRONT_AND_BACK:
+         return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT
+              | BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
+      case GL_LEFT:
+         return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT;
+      case GL_FRONT_LEFT:
+         return BUFFER_BIT_FRONT_LEFT;
+      case GL_AUX0:
+         return BUFFER_BIT_AUX0;
+      case GL_AUX1:
+         return BUFFER_BIT_AUX1;
+      case GL_AUX2:
+         return BUFFER_BIT_AUX2;
+      case GL_AUX3:
+         return BUFFER_BIT_AUX3;
+      case GL_COLOR_ATTACHMENT0_EXT:
+         return BUFFER_BIT_COLOR0;
+      case GL_COLOR_ATTACHMENT1_EXT:
+         return BUFFER_BIT_COLOR1;
+      case GL_COLOR_ATTACHMENT2_EXT:
+         return BUFFER_BIT_COLOR2;
+      case GL_COLOR_ATTACHMENT3_EXT:
+         return BUFFER_BIT_COLOR3;
+      case GL_COLOR_ATTACHMENT4_EXT:
+         return BUFFER_BIT_COLOR4;
+      case GL_COLOR_ATTACHMENT5_EXT:
+         return BUFFER_BIT_COLOR5;
+      case GL_COLOR_ATTACHMENT6_EXT:
+         return BUFFER_BIT_COLOR6;
+      case GL_COLOR_ATTACHMENT7_EXT:
+         return BUFFER_BIT_COLOR7;
+      default:
+         /* error */
+         return BAD_MASK;
+   }
+}
 
-   FLUSH_VERTICES(ctx, _NEW_COLOR);
-   COPY_CHAN4(ctx->Color.ClearColor, tmp);
 
-   if (ctx->Visual.rgbMode && ctx->Driver.ClearColor) {
-      /* it's OK to call glClearColor in CI mode but it should be a NOP */
-      (*ctx->Driver.ClearColor)(ctx, ctx->Color.ClearColor);
+/**
+ * Helper routine used by glReadBuffer.
+ * Given a GLenum naming a color buffer, return the index of the corresponding
+ * renderbuffer (a BUFFER_* value).
+ * return -1 for an invalid buffer.
+ */
+static GLint
+read_buffer_enum_to_index(GLenum buffer)
+{
+   switch (buffer) {
+      case GL_FRONT:
+         return BUFFER_FRONT_LEFT;
+      case GL_BACK:
+         return BUFFER_BACK_LEFT;
+      case GL_RIGHT:
+         return BUFFER_FRONT_RIGHT;
+      case GL_FRONT_RIGHT:
+         return BUFFER_FRONT_RIGHT;
+      case GL_BACK_RIGHT:
+         return BUFFER_BACK_RIGHT;
+      case GL_BACK_LEFT:
+         return BUFFER_BACK_LEFT;
+      case GL_LEFT:
+         return BUFFER_FRONT_LEFT;
+      case GL_FRONT_LEFT:
+         return BUFFER_FRONT_LEFT;
+      case GL_AUX0:
+         return BUFFER_AUX0;
+      case GL_AUX1:
+         return BUFFER_AUX1;
+      case GL_AUX2:
+         return BUFFER_AUX2;
+      case GL_AUX3:
+         return BUFFER_AUX3;
+      case GL_COLOR_ATTACHMENT0_EXT:
+         return BUFFER_COLOR0;
+      case GL_COLOR_ATTACHMENT1_EXT:
+         return BUFFER_COLOR1;
+      case GL_COLOR_ATTACHMENT2_EXT:
+         return BUFFER_COLOR2;
+      case GL_COLOR_ATTACHMENT3_EXT:
+         return BUFFER_COLOR3;
+      case GL_COLOR_ATTACHMENT4_EXT:
+         return BUFFER_COLOR4;
+      case GL_COLOR_ATTACHMENT5_EXT:
+         return BUFFER_COLOR5;
+      case GL_COLOR_ATTACHMENT6_EXT:
+         return BUFFER_COLOR6;
+      case GL_COLOR_ATTACHMENT7_EXT:
+         return BUFFER_COLOR7;
+      default:
+         /* error */
+         return -1;
    }
 }
 
 
-
-void
-_mesa_Clear( GLbitfield mask )
+/**
+ * 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_DrawBuffersARB
+ *
+ * \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 (Name=0) or
+ * a user-created framebuffer object (Name!=0).
+ *   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);
-   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);
-
-   if (MESA_VERBOSE & VERBOSE_API)
-      fprintf(stderr, "glClear 0x%x\n", mask);
+   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx); /* too complex... */
 
-   if (ctx->NewState) {
-      gl_update_state( ctx );	/* update _Xmin, etc */
+   if (MESA_VERBOSE & VERBOSE_API) {
+      _mesa_debug(ctx, "glDrawBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
    }
 
-   if (ctx->RenderMode==GL_RENDER) {
-      const GLint x = ctx->DrawBuffer->_Xmin;
-      const GLint y = ctx->DrawBuffer->_Ymin;
-      const GLint height = ctx->DrawBuffer->_Ymax - ctx->DrawBuffer->_Ymin;
-      const GLint width  = ctx->DrawBuffer->_Xmax - ctx->DrawBuffer->_Xmin;
-      GLbitfield ddMask;
-
-      /* don't clear depth buffer if depth writing disabled */
-      if (!ctx->Depth.Mask)
-         CLEAR_BITS(mask, GL_DEPTH_BUFFER_BIT);
-
-      /* Build bitmask to send to driver Clear function */
-      ddMask = mask & (GL_DEPTH_BUFFER_BIT |
-                       GL_STENCIL_BUFFER_BIT |
-                       GL_ACCUM_BUFFER_BIT);
-      if (mask & GL_COLOR_BUFFER_BIT) {
-         ddMask |= ctx->Color.DrawDestMask;
+   if (buffer == GL_NONE) {
+      destMask = 0x0;
+   }
+   else {
+      const GLbitfield supportedMask
+         = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
+      destMask = draw_buffer_enum_to_bitmask(buffer);
+      if (destMask == BAD_MASK) {
+         /* totally bogus buffer */
+         _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffer(buffer)");
+         return;
+      }
+      destMask &= supportedMask;
+      if (destMask == 0x0) {
+         /* none of the named color buffers exist! */
+         _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffer(buffer)");
+         return;
       }
-
-      ASSERT(ctx->Driver.Clear);
-      ctx->Driver.Clear( ctx, ddMask, !ctx->Scissor.Enabled,
-			 x, y, width, height );
    }
+
+   /* 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);
 }
 
 
-void
-_mesa_DrawBuffer( GLenum mode )
+/**
+ * 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_DrawBuffersARB(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); /* too complex... */
+   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);
 
+   if (!ctx->Extensions.ARB_draw_buffers) {
+      _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB");
+      return;
+   }
+   if (n < 1 || n > (GLsizei) ctx->Const.MaxDrawBuffers) {
+      _mesa_error(ctx, GL_INVALID_VALUE, "glDrawBuffersARB(n)");
+      return;
+   }
 
-   if (MESA_VERBOSE & VERBOSE_API)
-      fprintf(stderr, "glDrawBuffer %s\n", gl_lookup_enum_by_nr(mode));
+   supportedMask = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
+   usedBufferMask = 0x0;
 
-   switch (mode) {
-      case GL_AUX0:
-      case GL_AUX1:
-      case GL_AUX2:
-      case GL_AUX3:
-         /* AUX buffers not implemented in Mesa at this time */
-         gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
-         return;
-      case GL_RIGHT:
-         if (!ctx->Visual.stereoMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
-            return;}
-         if (ctx->Visual.doubleBufferMode)
-            ctx->Color.DrawDestMask = FRONT_RIGHT_BIT | BACK_RIGHT_BIT;
-         else
-            ctx->Color.DrawDestMask = FRONT_RIGHT_BIT;
-         break;
-      case GL_FRONT_RIGHT:
-         if (!ctx->Visual.stereoMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
-            return;
-         }
-         ctx->Color.DrawDestMask = FRONT_RIGHT_BIT;
-         break;
-      case GL_BACK_RIGHT:
-         if (!ctx->Visual.stereoMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
-            return;
-         }
-         if (!ctx->Visual.doubleBufferMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
+   /* 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;
-         }
-         ctx->Color.DrawDestMask = BACK_RIGHT_BIT;
-         break;
-      case GL_BACK_LEFT:
-         if (!ctx->Visual.doubleBufferMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
+         }         
+         destMask[output] &= supportedMask;
+         if (destMask[output] == 0) {
+            _mesa_error(ctx, GL_INVALID_OPERATION,
+                        "glDrawBuffersARB(unsupported buffer)");
             return;
          }
-         ctx->Color.DrawDestMask = BACK_LEFT_BIT;
-         break;
-      case GL_FRONT_AND_BACK:
-         if (!ctx->Visual.doubleBufferMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
+         if (destMask[output] & usedBufferMask) {
+            /* can't specify a dest buffer more than once! */
+            _mesa_error(ctx, GL_INVALID_OPERATION,
+                        "glDrawBuffersARB(duplicated buffer)");
             return;
          }
-         if (ctx->Visual.stereoMode)
-            ctx->Color.DrawDestMask = FRONT_LEFT_BIT | BACK_LEFT_BIT
-                                    | FRONT_RIGHT_BIT | BACK_RIGHT_BIT;
-         else
-            ctx->Color.DrawDestMask = FRONT_LEFT_BIT | BACK_LEFT_BIT;
-         break;
-      case GL_BACK:
-         if (!ctx->Visual.doubleBufferMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glDrawBuffer" );
-            return;
-         }
-         if (ctx->Visual.stereoMode)
-            ctx->Color.DrawDestMask = BACK_LEFT_BIT | BACK_RIGHT_BIT;
-         else
-            ctx->Color.DrawDestMask = BACK_LEFT_BIT;
-         break;
-      case GL_LEFT:
-         /* never an error */
-         if (ctx->Visual.doubleBufferMode)
-            ctx->Color.DrawDestMask = FRONT_LEFT_BIT | BACK_LEFT_BIT;
-         else
-            ctx->Color.DrawDestMask = FRONT_LEFT_BIT;
-         break;
-      case GL_FRONT_LEFT:
-         /* never an error */
-         ctx->Color.DrawDestMask = FRONT_LEFT_BIT;
-         break;
-      case GL_FRONT:
-         /* never an error */
-         if (ctx->Visual.stereoMode)
-            ctx->Color.DrawDestMask = FRONT_LEFT_BIT | FRONT_RIGHT_BIT;
-         else
-            ctx->Color.DrawDestMask = FRONT_LEFT_BIT;
-         break;
-      case GL_NONE:
-         /* never an error */
-         ctx->Color.DrawDestMask = 0;
-         break;
-      default:
-         gl_error( ctx, GL_INVALID_ENUM, "glDrawBuffer" );
-         return;
+
+         /* update bitmask */
+         usedBufferMask |= destMask[output];
+      }
    }
 
-   /*
-    * Make the dest buffer mode more precise if possible
-    */
-   if (mode == GL_LEFT && !ctx->Visual.doubleBufferMode)
-      ctx->Color.DriverDrawBuffer = GL_FRONT_LEFT;
-   else if (mode == GL_RIGHT && !ctx->Visual.doubleBufferMode)
-      ctx->Color.DriverDrawBuffer = GL_FRONT_RIGHT;
-   else if (mode == GL_FRONT && !ctx->Visual.stereoMode)
-      ctx->Color.DriverDrawBuffer = GL_FRONT_LEFT;
-   else if (mode == GL_BACK && !ctx->Visual.stereoMode)
-      ctx->Color.DriverDrawBuffer = GL_BACK_LEFT;
-   else
-      ctx->Color.DriverDrawBuffer = mode;
+   /* OK, if we get here, there were no errors so set the new state */
+   _mesa_drawbuffers(ctx, n, buffers, destMask);
 
    /*
-    * Set current alpha buffer pointer
+    * Call device driver function.
     */
-   if (ctx->DrawBuffer->UseSoftwareAlphaBuffers) {
-      if (ctx->Color.DriverDrawBuffer == GL_FRONT_LEFT)
-         ctx->DrawBuffer->Alpha = ctx->DrawBuffer->FrontLeftAlpha;
-      else if (ctx->Color.DriverDrawBuffer == GL_BACK_LEFT)
-         ctx->DrawBuffer->Alpha = ctx->DrawBuffer->BackLeftAlpha;
-      else if (ctx->Color.DriverDrawBuffer == GL_FRONT_RIGHT)
-         ctx->DrawBuffer->Alpha = ctx->DrawBuffer->FrontRightAlpha;
-      else if (ctx->Color.DriverDrawBuffer == GL_BACK_RIGHT)
-         ctx->DrawBuffer->Alpha = ctx->DrawBuffer->BackRightAlpha;
+   if (ctx->Driver.DrawBuffers)
+      ctx->Driver.DrawBuffers(ctx, n, buffers);
+   else if (ctx->Driver.DrawBuffer)
+      ctx->Driver.DrawBuffer(ctx, buffers[0]);
+}
+
+
+/**
+ * Helper function to set the GL_DRAW_BUFFER state in the context and
+ * current FBO.
+ *
+ * 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];
+
+   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 we get here there can't have been an error.
-    * Now see if device driver can implement the drawing to the target
-    * buffer(s).  The driver may not be able to do GL_FRONT_AND_BACK mode
-    * for example.  We'll take care of that in the core code by looping
-    * over the individual buffers.
-    */
-   ASSERT(ctx->Driver.SetDrawBuffer);
-   if ( (*ctx->Driver.SetDrawBuffer)(ctx, ctx->Color.DriverDrawBuffer) ) {
-      /* All OK, the driver will do all buffer writes */
-      ctx->Color.MultiDrawBuffer = GL_FALSE;
+   if (n == 1) {
+      GLuint buf, count = 0;
+      /* init to -1 to help catch errors */
+      fb->_ColorDrawBufferIndexes[0] = -1;
+      for (buf = 0; buf < BUFFER_COUNT; buf++) {
+         if (destMask[0] & (1 << buf)) {
+            fb->_ColorDrawBufferIndexes[count] = buf;
+            count++;
+         }
+      }
+      fb->ColorDrawBuffer[0] = buffers[0];
+      fb->_NumColorDrawBuffers = count;
    }
    else {
-      /* We'll have to loop over the multiple draw buffer targets */
-      ctx->Color.MultiDrawBuffer = GL_TRUE;
-      /* Set drawing buffer to front for now */
-      (void) (*ctx->Driver.SetDrawBuffer)(ctx, GL_FRONT_LEFT);
+      GLuint buf, count = 0;
+      for (buf = 0; buf < n; buf++ ) {
+         if (destMask[buf]) {
+            fb->_ColorDrawBufferIndexes[buf] = _mesa_ffs(destMask[buf]) - 1;
+            fb->ColorDrawBuffer[buf] = buffers[buf];
+            count = buf + 1;
+         }
+         else {
+            fb->_ColorDrawBufferIndexes[buf] = -1;
+         }
+      }
+      /* set remaining outputs to -1 (GL_NONE) */
+      while (buf < ctx->Const.MaxDrawBuffers) {
+         fb->_ColorDrawBufferIndexes[buf] = -1;
+         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++) {
+         ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
+      }
    }
 
-   ctx->Color.DrawBuffer = mode;
    ctx->NewState |= _NEW_COLOR;
 }
 
 
-
+/**
+ * Like \sa _mesa_drawbuffers(), this is a helper function for setting
+ * GL_READ_BUFFER state in the context and current FBO.
+ * \param ctx  the rendering context
+ * \param buffer  GL_FRONT, GL_BACK, GL_COLOR_ATTACHMENT0, etc.
+ * \param bufferIndex  the numerical index corresponding to 'buffer'
+ */
 void
-_mesa_ReadBuffer( GLenum mode )
+_mesa_readbuffer(GLcontext *ctx, GLenum buffer, GLint bufferIndex)
 {
-   GET_CURRENT_CONTEXT(ctx);
-   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);
+   struct gl_framebuffer *fb = ctx->ReadBuffer;
 
-   if (MESA_VERBOSE & VERBOSE_API)
-      fprintf(stderr, "glReadBuffer %s\n", gl_lookup_enum_by_nr(mode));
-
-   switch (mode) {
-      case GL_AUX0:
-      case GL_AUX1:
-      case GL_AUX2:
-      case GL_AUX3:
-         /* AUX buffers not implemented in Mesa at this time */
-         gl_error( ctx, GL_INVALID_OPERATION, "glReadBuffer" );
-         return;
-      case GL_LEFT:
-      case GL_FRONT:
-      case GL_FRONT_LEFT:
-         /* Front-Left buffer, always exists */
-         ctx->Pixel.DriverReadBuffer = GL_FRONT_LEFT;
-         break;
-      case GL_BACK:
-      case GL_BACK_LEFT:
-         /* Back-Left buffer, requires double buffering */
-         if (!ctx->Visual.doubleBufferMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glReadBuffer" );
-            return;
-         }
-         ctx->Pixel.DriverReadBuffer = GL_BACK_LEFT;
-         break;
-      case GL_FRONT_RIGHT:
-      case GL_RIGHT:
-         if (!ctx->Visual.stereoMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glReadBuffer" );
-            return;
-         }
-         ctx->Pixel.DriverReadBuffer = GL_FRONT_RIGHT;
-         break;
-      case GL_BACK_RIGHT:
-         if (!ctx->Visual.stereoMode || !ctx->Visual.doubleBufferMode) {
-            gl_error( ctx, GL_INVALID_OPERATION, "glReadBuffer" );
-            return;
-         }
-         ctx->Pixel.DriverReadBuffer = GL_BACK_RIGHT;
-         break;
-      default:
-         gl_error( ctx, GL_INVALID_ENUM, "glReadBuffer" );
-         return;
+   if (fb->Name == 0) {
+      /* Only update the per-context READ_BUFFER state if we're bound to
+       * a window-system framebuffer.
+       */
+      ctx->Pixel.ReadBuffer = buffer;
    }
 
-   ctx->Pixel.ReadBuffer = mode;
+   fb->ColorReadBuffer = buffer;
+   fb->_ColorReadBufferIndex = bufferIndex;
+
    ctx->NewState |= _NEW_PIXEL;
 }
 
 
-/*
- * GL_MESA_resize_buffers extension
+
+/**
+ * Called by glReadBuffer to set the source renderbuffer for reading pixels.
+ * \param mode color buffer such as GL_FRONT, GL_BACK, etc.
  */
-void
-_mesa_ResizeBuffersMESA( void )
+void GLAPIENTRY
+_mesa_ReadBuffer(GLenum buffer)
 {
-   GLcontext *ctx = _mesa_get_current_context();
-   GLuint buf_width, buf_height;
-   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH( ctx );
-
+   struct gl_framebuffer *fb;
+   GLbitfield supportedMask;
+   GLint srcBuffer;
+   GET_CURRENT_CONTEXT(ctx);
+   ASSERT_OUTSIDE_BEGIN_END_AND_FLUSH(ctx);
 
    if (MESA_VERBOSE & VERBOSE_API)
-      fprintf(stderr, "glResizeBuffersMESA\n");
+      _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 
-   /* ask device driver for size of output buffer */
-   (*ctx->Driver.GetBufferSize)( ctx, &buf_width, &buf_height );
+   fb = ctx->ReadBuffer;
 
-   /* see if size of device driver's color buffer (window) has changed */
-   if (ctx->DrawBuffer->Width == (GLint) buf_width &&
-       ctx->DrawBuffer->Height == (GLint) buf_height)
-      return;
+   if (MESA_VERBOSE & VERBOSE_API)
+      _mesa_debug(ctx, "glReadBuffer %s\n", _mesa_lookup_enum_by_nr(buffer));
 
-   ctx->NewState |= _NEW_BUFFERS;  /* to update scissor / window bounds */
+   if (fb->Name > 0 && 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 */
 
-   /* save buffer size */
-   ctx->DrawBuffer->Width = buf_width;
-   ctx->DrawBuffer->Height = buf_height;
+   _mesa_readbuffer(ctx, buffer, srcBuffer);
 
-   ctx->Driver.ResizeBuffersMESA( ctx );
+   /*
+    * Call device driver function.
+    */
+   if (ctx->Driver.ReadBuffer)
+      (*ctx->Driver.ReadBuffer)(ctx, buffer);
 }