Replace gl_framebuffer's _ColorDrawBufferMask with _ColorDrawBufferIndexes

Each array element is now a BUFFER_x token rather than a BUFFER_BIT_x bitmask.
The number of active color buffers is specified by _NumColorDrawBuffers.
This builds on the previous DrawBuffer changes and will help with drivers
implementing GL_ARB_draw_buffers.

34 files changed, 230 insertions, 216 deletions

diff --git a/src/mesa/drivers/dri/i810/i810context.c b/src/mesa/drivers/dri/i810/i810context.c
index 3f7f2cc8a4..9e09bddea3 100644
--- a/src/mesa/drivers/dri/i810/i810context.c
+++ b/src/mesa/drivers/dri/i810/i810context.c
@@ -424,11 +424,11 @@ void i810XMesaSetBackClipRects( i810ContextPtr imesa )
 static void i810XMesaWindowMoved( i810ContextPtr imesa )
 {
    /* Determine current color drawing buffer */
-   switch (imesa->glCtx->DrawBuffer->_ColorDrawBufferMask[0]) {
-   case BUFFER_BIT_FRONT_LEFT:
+   switch (imesa->glCtx->DrawBuffer->_ColorDrawBufferIndexes[0]) {
+   case BUFFER_FRONT_LEFT:
       i810XMesaSetFrontClipRects( imesa );
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       i810XMesaSetBackClipRects( imesa );
       break;
    default:
@@ -486,11 +486,11 @@ i810UpdatePageFlipping( i810ContextPtr imesa )
    int front = 0;
 
    /* Determine current color drawing buffer */
-   switch (ctx->DrawBuffer->_ColorDrawBufferMask[0]) {
-   case BUFFER_BIT_FRONT_LEFT:
+   switch (ctx->DrawBuffer->_ColorDrawBufferIndexes[0]) {
+   case BUFFER_FRONT_LEFT:
       front = 1;
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       front = 0;
       break;
    default:
diff --git a/src/mesa/drivers/dri/i810/i810state.c b/src/mesa/drivers/dri/i810/i810state.c
index e0d5b2b487..185c098b5e 100644
--- a/src/mesa/drivers/dri/i810/i810state.c
+++ b/src/mesa/drivers/dri/i810/i810state.c
@@ -292,18 +292,20 @@ void i810DrawBuffer(GLcontext *ctx, GLenum mode )
    i810ContextPtr imesa = I810_CONTEXT(ctx);
    int front = 0;
   
-   /*
-    * _DrawDestMask is easier to cope with than <mode>.
-    */
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0]) {
-   case BUFFER_BIT_FRONT_LEFT:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
+      FALLBACK( imesa, I810_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0]) {
+   case BUFFER_FRONT_LEFT:
      front = 1;
      break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
      front = 0;
      break;
    default:
-      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
       FALLBACK( imesa, I810_FALLBACK_DRAW_BUFFER, GL_TRUE );
       return;
    }
diff --git a/src/mesa/drivers/dri/i915/intel_context.c b/src/mesa/drivers/dri/i915/intel_context.c
index 99ea37d227..2cb57f3a92 100644
--- a/src/mesa/drivers/dri/i915/intel_context.c
+++ b/src/mesa/drivers/dri/i915/intel_context.c
@@ -788,9 +788,7 @@ void LOCK_HARDWARE( struct intel_context *intel )
        if (intel_fb)
 	  intel_rb =
 	     intel_get_renderbuffer(&intel_fb->Base,
-				    intel_fb->Base._ColorDrawBufferMask[0] ==
-				    BUFFER_BIT_FRONT_LEFT ? BUFFER_FRONT_LEFT :
-				    BUFFER_BACK_LEFT);
+				    intel_fb->Base._ColorDrawBufferIndexes[0]);
     }
 
     if (intel_rb && dPriv->vblFlags &&
diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
index 5a6ef463ea..a4645effd4 100644
--- a/src/mesa/drivers/dri/i965/brw_context.h
+++ b/src/mesa/drivers/dri/i965/brw_context.h
@@ -463,7 +463,9 @@ struct brw_context
       struct intel_region *saved_draw_region;
       struct intel_region *saved_depth_region;
 
-      GLuint restore_draw_mask;
+      GLuint restore_draw_buffers[MAX_DRAW_BUFFERS];
+      GLuint restore_num_draw_buffers;
+
       struct gl_fragment_program *restore_fp;
       
       GLboolean active;
diff --git a/src/mesa/drivers/dri/i965/brw_metaops.c b/src/mesa/drivers/dri/i965/brw_metaops.c
index 87da464f1b..005489689f 100644
--- a/src/mesa/drivers/dri/i965/brw_metaops.c
+++ b/src/mesa/drivers/dri/i965/brw_metaops.c
@@ -156,7 +156,7 @@ static const char *fp_tex_prog =
  *   FragmentProgram->_Current
  *   VertexProgram->_Enabled
  *   brw->vertex_program
- *   DrawBuffer->_ColorDrawBufferMask[0]
+ *   DrawBuffer->_ColorDrawBufferIndexes[0]
  * 
  *
  * More if drawpixels-through-texture is added.  
@@ -481,6 +481,7 @@ static void install_meta_state( struct intel_context *intel )
 {
    GLcontext *ctx = &intel->ctx;
    struct brw_context *brw = brw_context(ctx);
+   GLuint i;
 
    if (!brw->metaops.vbo) {
       init_metaops_state(brw);
@@ -490,7 +491,12 @@ static void install_meta_state( struct intel_context *intel )
    
    meta_no_texture(&brw->intel);
    meta_flat_shade(&brw->intel);
-   brw->metaops.restore_draw_mask = ctx->DrawBuffer->_ColorDrawBufferMask[0];
+   for (i = 0; i < ctx->Const.MaxDrawBuffers; i++) {
+      brw->metaops.restore_draw_buffers[i]
+         = ctx->DrawBuffer->_ColorDrawBufferIndexes[i];
+   }
+   brw->metaops.restore_num_draw_buffers = ctx->DrawBuffer->_NumColorDrawBuffers;
+
    brw->metaops.restore_fp = ctx->FragmentProgram.Current;
 
    /* This works without adjusting refcounts.  Fix later? 
@@ -506,10 +512,16 @@ static void leave_meta_state( struct intel_context *intel )
 {
    GLcontext *ctx = &intel->ctx;
    struct brw_context *brw = brw_context(ctx);
+   GLuint i;
 
    restore_attribs(brw);
 
-   ctx->DrawBuffer->_ColorDrawBufferMask[0] = brw->metaops.restore_draw_mask;
+   for (i = 0; i < ctx->Const.MaxDrawBuffers; i++) {
+      ctx->DrawBuffer->_ColorDrawBufferIndexes[i]
+         = brw->metaops.restore_draw_buffers[i];
+   }
+   ctx->DrawBuffer->_NumColorDrawBuffers = brw->metaops.restore_num_draw_buffers;
+
    ctx->FragmentProgram.Current = brw->metaops.restore_fp;
 
    brw->state.draw_region = brw->metaops.saved_draw_region;
diff --git a/src/mesa/drivers/dri/intel/intel_blit.c b/src/mesa/drivers/dri/intel/intel_blit.c
index 479c30669c..72b17dd71f 100644
--- a/src/mesa/drivers/dri/intel/intel_blit.c
+++ b/src/mesa/drivers/dri/intel/intel_blit.c
@@ -98,10 +98,10 @@ intelCopyBuffer(const __DRIdrawablePrivate * dPriv,
 
       ASSERT(intel_fb);
       ASSERT(intel_fb->Base.Name == 0);    /* Not a user-created FBO */
-      ASSERT(frontRegion);
-      ASSERT(backRegion);
-      ASSERT(frontRegion->pitch == backRegion->pitch);
-      ASSERT(frontRegion->cpp == backRegion->cpp);
+      ASSERT(src);
+      ASSERT(dst);
+      ASSERT(src->pitch == dst->pitch);
+      ASSERT(src->cpp == dst->cpp);
 
       if (cpp == 2) {
 	 BR13 = (0xCC << 16) | (1 << 24);
@@ -357,7 +357,7 @@ intelEmitCopyBlit(struct intel_context *intel,
 
 /**
  * Use blitting to clear the renderbuffers named by 'flags'.
- * Note: we can't use the ctx->DrawBuffer->_ColorDrawBufferMask field
+ * Note: we can't use the ctx->DrawBuffer->_ColorDrawBufferIndexes field
  * since that might include software renderbuffers or renderbuffers
  * which we're clearing with triangles.
  * \param mask  bitmask of BUFFER_BIT_* values indicating buffers to clear
diff --git a/src/mesa/drivers/dri/intel/intel_buffers.c b/src/mesa/drivers/dri/intel/intel_buffers.c
index c654474200..2ea8d683eb 100644
--- a/src/mesa/drivers/dri/intel/intel_buffers.c
+++ b/src/mesa/drivers/dri/intel/intel_buffers.c
@@ -290,15 +290,14 @@ intelWindowMoved(struct intel_context *intel)
    }
    else {
       /* drawing to a window */
-      switch (intel_fb->Base._ColorDrawBufferMask[0]) {
-      case BUFFER_BIT_FRONT_LEFT:
+      switch (intel_fb->Base._ColorDrawBufferIndexes[0]) {
+      case BUFFER_FRONT_LEFT:
          intelSetFrontClipRects(intel);
          break;
-      case BUFFER_BIT_BACK_LEFT:
+      case BUFFER_BACK_LEFT:
          intelSetBackClipRects(intel);
          break;
       default:
-         /* glDrawBuffer(GL_NONE or GL_FRONT_AND_BACK): software fallback */
          intelSetFrontClipRects(intel);
       }
    }
@@ -623,8 +622,8 @@ intel_wait_flips(struct intel_context *intel, GLuint batch_flags)
       (struct intel_framebuffer *) intel->ctx.DrawBuffer;
    struct intel_renderbuffer *intel_rb =
       intel_get_renderbuffer(&intel_fb->Base,
-			     intel_fb->Base._ColorDrawBufferMask[0] ==
-			     BUFFER_BIT_FRONT_LEFT ? BUFFER_FRONT_LEFT :
+			     intel_fb->Base._ColorDrawBufferIndexes[0] ==
+			     BUFFER_FRONT_LEFT ? BUFFER_FRONT_LEFT :
 			     BUFFER_BACK_LEFT);
 
    if (intel_fb->Base.Name == 0 && intel_rb &&
@@ -944,7 +943,7 @@ intel_draw_buffer(GLcontext * ctx, struct gl_framebuffer *fb)
       /* draw to exactly one color buffer */
       /*_mesa_debug(ctx, "Hardware rendering\n");*/
       FALLBACK(intel, INTEL_FALLBACK_DRAW_BUFFER, GL_FALSE);
-      if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT) {
+      if (fb->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT) {
          front = 1;
       }
 
diff --git a/src/mesa/drivers/dri/intel/intel_fbo.c b/src/mesa/drivers/dri/intel/intel_fbo.c
index 8d75c63cef..84ac7889b2 100644
--- a/src/mesa/drivers/dri/intel/intel_fbo.c
+++ b/src/mesa/drivers/dri/intel/intel_fbo.c
@@ -71,7 +71,10 @@ intel_renderbuffer(struct gl_renderbuffer *rb)
 struct intel_renderbuffer *
 intel_get_renderbuffer(struct gl_framebuffer *fb, GLuint attIndex)
 {
-   return intel_renderbuffer(fb->Attachment[attIndex].Renderbuffer);
+   if (attIndex >= 0)
+      return intel_renderbuffer(fb->Attachment[attIndex].Renderbuffer);
+   else
+      return NULL;
 }
 
 
diff --git a/src/mesa/drivers/dri/mach64/mach64_lock.c b/src/mesa/drivers/dri/mach64/mach64_lock.c
index b73e350111..13e212b81d 100644
--- a/src/mesa/drivers/dri/mach64/mach64_lock.c
+++ b/src/mesa/drivers/dri/mach64/mach64_lock.c
@@ -70,7 +70,7 @@ void mach64GetLock( mach64ContextPtr mmesa, GLuint flags )
 
    if ( mmesa->lastStamp != dPriv->lastStamp ) {
       mmesa->lastStamp = dPriv->lastStamp;
-      if (mmesa->glCtx->DrawBuffer->_ColorDrawBufferMask[0] == BUFFER_BIT_BACK_LEFT)
+      if (mmesa->glCtx->DrawBuffer->_ColorDrawBufferIndexes[0] == BUFFER_BACK_LEFT)
          mach64SetCliprects( mmesa->glCtx, GL_BACK_LEFT );
       else
          mach64SetCliprects( mmesa->glCtx, GL_FRONT_LEFT );
diff --git a/src/mesa/drivers/dri/mach64/mach64_state.c b/src/mesa/drivers/dri/mach64/mach64_state.c
index 667a394520..10a5b40ba1 100644
--- a/src/mesa/drivers/dri/mach64/mach64_state.c
+++ b/src/mesa/drivers/dri/mach64/mach64_state.c
@@ -726,24 +726,26 @@ static void mach64DDDrawBuffer( GLcontext *ctx, GLenum mode )
 
    FLUSH_BATCH( mmesa );
 
-   /*
-    * _DrawDestMask is easier to cope with than <mode>.
-    */
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
+      FALLBACK( mmesa, MACH64_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
       FALLBACK( mmesa, MACH64_FALLBACK_DRAW_BUFFER, GL_FALSE );
       mach64SetCliprects( ctx, GL_FRONT_LEFT );
       if (MACH64_DEBUG & DEBUG_VERBOSE_MSG)
 	 fprintf(stderr,"%s: BUFFER_BIT_FRONT_LEFT\n", __FUNCTION__);
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       FALLBACK( mmesa, MACH64_FALLBACK_DRAW_BUFFER, GL_FALSE );
       mach64SetCliprects( ctx, GL_BACK_LEFT );
       if (MACH64_DEBUG & DEBUG_VERBOSE_MSG)
 	 fprintf(stderr,"%s: BUFFER_BIT_BACK_LEFT\n", __FUNCTION__);
       break;
    default:
-      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
       FALLBACK( mmesa, MACH64_FALLBACK_DRAW_BUFFER, GL_TRUE );
       if (MACH64_DEBUG & DEBUG_VERBOSE_MSG)
 	 fprintf(stderr,"%s: fallback (mode=%d)\n", __FUNCTION__, mode);
diff --git a/src/mesa/drivers/dri/mga/mgastate.c b/src/mesa/drivers/dri/mga/mgastate.c
index 88f2175cc3..1d413d3473 100644
--- a/src/mesa/drivers/dri/mga/mgastate.c
+++ b/src/mesa/drivers/dri/mga/mgastate.c
@@ -799,20 +799,22 @@ static void mgaDDDrawBuffer(GLcontext *ctx, GLenum mode )
 
    FLUSH_BATCH( mmesa );
 
-   /*
-    * _DrawDestMask is easier to cope with than <mode>.
-    */
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
+      FALLBACK( ctx, MGA_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
       mmesa->setup.dstorg = mmesa->mgaScreen->frontOffset;
       mmesa->draw_buffer = MGA_FRONT;
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       mmesa->setup.dstorg = mmesa->mgaScreen->backOffset;
       mmesa->draw_buffer = MGA_BACK;
       break;
    default:
-      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
       FALLBACK( ctx, MGA_FALLBACK_DRAW_BUFFER, GL_TRUE );
       return;
    }
diff --git a/src/mesa/drivers/dri/nouveau/nouveau_context.c b/src/mesa/drivers/dri/nouveau/nouveau_context.c
index 4f4128c875..f18dd64490 100644
--- a/src/mesa/drivers/dri/nouveau/nouveau_context.c
+++ b/src/mesa/drivers/dri/nouveau/nouveau_context.c
@@ -328,7 +328,7 @@ nouveauDoSwapBuffers(nouveauContextPtr nmesa, __DRIdrawablePrivate *dPriv)
 	int nbox, i;
 
 	fb = (struct gl_framebuffer *)dPriv->driverPrivate;
-	if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT) {
+	if (fb->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT) {
 		src = (nouveau_renderbuffer_t *)
 			fb->Attachment[BUFFER_FRONT_LEFT].Renderbuffer;
 	} else {
diff --git a/src/mesa/drivers/dri/nouveau/nouveau_driver.c b/src/mesa/drivers/dri/nouveau/nouveau_driver.c
index 1135817fe9..7bd42fdfe2 100644
--- a/src/mesa/drivers/dri/nouveau/nouveau_driver.c
+++ b/src/mesa/drivers/dri/nouveau/nouveau_driver.c
@@ -119,7 +119,7 @@ static void nouveauFlush( GLcontext *ctx )
 {
 	nouveauContextPtr nmesa = NOUVEAU_CONTEXT(ctx);
 
-	if (ctx->DrawBuffer->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT)
+	if (ctx->DrawBuffer->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT)
 		nouveauDoSwapBuffers(nmesa, nmesa->driDrawable);
 	FIRE_RING();
 }
diff --git a/src/mesa/drivers/dri/r128/r128_state.c b/src/mesa/drivers/dri/r128/r128_state.c
index f1e92d7a7a..2abe59056e 100644
--- a/src/mesa/drivers/dri/r128/r128_state.c
+++ b/src/mesa/drivers/dri/r128/r128_state.c
@@ -897,18 +897,22 @@ static void r128DDDrawBuffer( GLcontext *ctx, GLenum mode )
 
    FLUSH_BATCH( rmesa );
 
-   /*
-    * _ColorDrawBufferMask is easier to cope with than <mode>.
-    */
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
-   case BUFFER_BIT_BACK_LEFT:
-      FALLBACK( rmesa, R128_FALLBACK_DRAW_BUFFER, GL_FALSE );
-      break;
-   default:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
       /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
       FALLBACK( rmesa, R128_FALLBACK_DRAW_BUFFER, GL_TRUE );
-      break;
+      return;
+   }
+   else {
+      switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+      case BUFFER_FRONT_LEFT:
+      case BUFFER_BACK_LEFT:
+         FALLBACK( rmesa, R128_FALLBACK_DRAW_BUFFER, GL_FALSE );
+         break;
+      default:
+         /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
+         FALLBACK( rmesa, R128_FALLBACK_DRAW_BUFFER, GL_TRUE );
+         break;
+      }
    }
 
    rmesa->new_state |= R128_NEW_WINDOW;
diff --git a/src/mesa/drivers/dri/r200/r200_state.c b/src/mesa/drivers/dri/r200/r200_state.c
index 1d975ecd57..cf375171c8 100644
--- a/src/mesa/drivers/dri/r200/r200_state.c
+++ b/src/mesa/drivers/dri/r200/r200_state.c
@@ -1859,8 +1859,7 @@ void r200SetCliprects( r200ContextPtr rmesa )
    GLframebuffer *const draw_fb = (GLframebuffer*) drawable->driverPrivate;
    GLframebuffer *const read_fb = (GLframebuffer*) readable->driverPrivate;
 
-   if (draw_fb->_ColorDrawBufferMask[0]
-       == BUFFER_BIT_BACK_LEFT) {
+   if (draw_fb->_ColorDrawBufferIndexes[0] == BUFFER_BIT_BACK_LEFT) {
       /* Can't ignore 2d windows if we are page flipping.
        */
       if ( drawable->numBackClipRects == 0 || rmesa->doPageFlip ) {
@@ -1910,17 +1909,18 @@ static void r200DrawBuffer( GLcontext *ctx, GLenum mode )
 
    R200_FIREVERTICES(rmesa);	/* don't pipeline cliprect changes */
 
-   /*
-    * _ColorDrawBufferMask is easier to cope with than <mode>.
-    * Check for software fallback, update cliprects.
-    */
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
-   case BUFFER_BIT_BACK_LEFT:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+      /* 0 (GL_NONE) buffers or multiple color drawing buffers */
+      FALLBACK( rmesa, R200_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
+   case BUFFER_BACK_LEFT:
       FALLBACK( rmesa, R200_FALLBACK_DRAW_BUFFER, GL_FALSE );
       break;
    default:
-      /* 0 (GL_NONE) buffers or multiple color drawing buffers */
       FALLBACK( rmesa, R200_FALLBACK_DRAW_BUFFER, GL_TRUE );
       return;
    }
@@ -2445,11 +2445,11 @@ r200UpdateDrawBuffer(GLcontext *ctx)
    struct gl_framebuffer *fb = ctx->DrawBuffer;
    driRenderbuffer *drb;
 
-   if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT) {
+   if (fb->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT) {
       /* draw to front */
       drb = (driRenderbuffer *) fb->Attachment[BUFFER_FRONT_LEFT].Renderbuffer;
    }
-   else if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_BACK_LEFT) {
+   else if (fb->_ColorDrawBufferIndexes[0] == BUFFER_BACK_LEFT) {
       /* draw to back */
       drb = (driRenderbuffer *) fb->Attachment[BUFFER_BACK_LEFT].Renderbuffer;
    }
diff --git a/src/mesa/drivers/dri/r300/r300_state.c b/src/mesa/drivers/dri/r300/r300_state.c
index 9491f98b47..b90f42234a 100644
--- a/src/mesa/drivers/dri/r300/r300_state.c
+++ b/src/mesa/drivers/dri/r300/r300_state.c
@@ -1007,12 +1007,12 @@ void r300UpdateDrawBuffer(GLcontext * ctx)
 	struct gl_framebuffer *fb = ctx->DrawBuffer;
 	driRenderbuffer *drb;
 
-	if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT) {
+	if (fb->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT) {
 		/* draw to front */
 		drb =
 		    (driRenderbuffer *) fb->Attachment[BUFFER_FRONT_LEFT].
 		    Renderbuffer;
-	} else if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_BACK_LEFT) {
+	} else if (fb->_ColorDrawBufferIndexes[0] == BUFFER_BACK_LEFT) {
 		/* draw to back */
 		drb =
 		    (driRenderbuffer *) fb->Attachment[BUFFER_BACK_LEFT].
diff --git a/src/mesa/drivers/dri/r300/radeon_lock.c b/src/mesa/drivers/dri/r300/radeon_lock.c
index bc3c2d6c6b..d54a821c63 100644
--- a/src/mesa/drivers/dri/r300/radeon_lock.c
+++ b/src/mesa/drivers/dri/r300/radeon_lock.c
@@ -68,8 +68,8 @@ void radeonUpdatePageFlipping(radeonContextPtr rmesa)
 	}
 
 	use_back = rmesa->glCtx->DrawBuffer ?
-	    (rmesa->glCtx->DrawBuffer->_ColorDrawBufferMask[0] ==
-	     BUFFER_BIT_BACK_LEFT) : 1;
+	    (rmesa->glCtx->DrawBuffer->_ColorDrawBufferIndexes[0] ==
+	     BUFFER_BACK_LEFT) : 1;
 	use_back ^= (rmesa->sarea->pfCurrentPage == 1);
 
 	if (use_back) {
diff --git a/src/mesa/drivers/dri/r300/radeon_state.c b/src/mesa/drivers/dri/r300/radeon_state.c
index 82bfd951b9..af2c3bcacd 100644
--- a/src/mesa/drivers/dri/r300/radeon_state.c
+++ b/src/mesa/drivers/dri/r300/radeon_state.c
@@ -152,7 +152,7 @@ void radeonSetCliprects(radeonContextPtr radeon)
 	GLframebuffer *const draw_fb = (GLframebuffer*)drawable->driverPrivate;
 	GLframebuffer *const read_fb = (GLframebuffer*)readable->driverPrivate;
 
-	if (draw_fb->_ColorDrawBufferMask[0] == BUFFER_BIT_BACK_LEFT) {
+	if (draw_fb->_ColorDrawBufferIndexes[0] == BUFFER_BACK_LEFT) {
 		/* Can't ignore 2d windows if we are page flipping. */
 		if (drawable->numBackClipRects == 0 || radeon->doPageFlip ||
 		    radeon->sarea->pfCurrentPage == 1) {
diff --git a/src/mesa/drivers/dri/radeon/radeon_state.c b/src/mesa/drivers/dri/radeon/radeon_state.c
index 4de05c7697..ae83c91d25 100644
--- a/src/mesa/drivers/dri/radeon/radeon_state.c
+++ b/src/mesa/drivers/dri/radeon/radeon_state.c
@@ -1640,8 +1640,7 @@ void radeonSetCliprects( radeonContextPtr rmesa )
    GLframebuffer *const draw_fb = (GLframebuffer*) drawable->driverPrivate;
    GLframebuffer *const read_fb = (GLframebuffer*) readable->driverPrivate;
 
-   if (draw_fb->_ColorDrawBufferMask[0]
-       == BUFFER_BIT_BACK_LEFT) {
+   if (draw_fb->_ColorDrawBufferIndexes[0] == BUFFER_BACK_LEFT) {
       /* Can't ignore 2d windows if we are page flipping.
        */
       if ( drawable->numBackClipRects == 0 || rmesa->doPageFlip ) {
@@ -1693,17 +1692,18 @@ static void radeonDrawBuffer( GLcontext *ctx, GLenum mode )
 
    RADEON_FIREVERTICES(rmesa);	/* don't pipeline cliprect changes */
 
-   /*
-    * _ColorDrawBufferMask is easier to cope with than <mode>.
-    * Check for software fallback, update cliprects.
-    */
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
-   case BUFFER_BIT_BACK_LEFT:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+      /* 0 (GL_NONE) buffers or multiple color drawing buffers */
+      FALLBACK( rmesa, RADEON_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
+   case BUFFER_BACK_LEFT:
       FALLBACK( rmesa, RADEON_FALLBACK_DRAW_BUFFER, GL_FALSE );
       break;
    default:
-      /* 0 (GL_NONE) buffers or multiple color drawing buffers */
       FALLBACK( rmesa, RADEON_FALLBACK_DRAW_BUFFER, GL_TRUE );
       return;
    }
@@ -2222,11 +2222,11 @@ radeonUpdateDrawBuffer(GLcontext *ctx)
    struct gl_framebuffer *fb = ctx->DrawBuffer;
    driRenderbuffer *drb;
 
-   if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT) {
+   if (fb->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT) {
       /* draw to front */
       drb = (driRenderbuffer *) fb->Attachment[BUFFER_FRONT_LEFT].Renderbuffer;
    }
-   else if (fb->_ColorDrawBufferMask[0] == BUFFER_BIT_BACK_LEFT) {
+   else if (fb->_ColorDrawBufferIndexes[0] == BUFFER_BACK_LEFT) {
       /* draw to back */
       drb = (driRenderbuffer *) fb->Attachment[BUFFER_BACK_LEFT].Renderbuffer;
    }
diff --git a/src/mesa/drivers/dri/savage/savage_xmesa.c b/src/mesa/drivers/dri/savage/savage_xmesa.c
index 013e88216f..f23409fcbc 100644
--- a/src/mesa/drivers/dri/savage/savage_xmesa.c
+++ b/src/mesa/drivers/dri/savage/savage_xmesa.c
@@ -730,7 +730,7 @@ void savageXMesaSetClipRects(savageContextPtr imesa)
    __DRIdrawablePrivate *dPriv = imesa->driDrawable;
 
    if ((dPriv->numBackClipRects == 0)
-       || (imesa->glCtx->DrawBuffer->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT)) {
+       || (imesa->glCtx->DrawBuffer->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT)) {
       imesa->numClipRects = dPriv->numClipRects;
       imesa->pClipRects = dPriv->pClipRects;
       imesa->drawX = dPriv->x;
diff --git a/src/mesa/drivers/dri/savage/savagestate.c b/src/mesa/drivers/dri/savage/savagestate.c
index 741a9dda4f..7c36b133a9 100644
--- a/src/mesa/drivers/dri/savage/savagestate.c
+++ b/src/mesa/drivers/dri/savage/savagestate.c
@@ -640,15 +640,17 @@ static void savageDDDrawBuffer(GLcontext *ctx, GLenum mode )
     savageContextPtr imesa = SAVAGE_CONTEXT(ctx);
     u_int32_t destCtrl = imesa->regs.s4.destCtrl.ui;
 
-    /*
-     * _DrawDestMask is easier to cope with than <mode>.
-     */
-    switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-    case BUFFER_BIT_FRONT_LEFT:
+    if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+	FALLBACK( ctx, SAVAGE_FALLBACK_DRAW_BUFFER, GL_TRUE );
+        return;
+    }
+
+    switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+    case BUFFER_FRONT_LEFT:
         imesa->IsDouble = GL_FALSE;
 	imesa->regs.s4.destCtrl.ni.offset = imesa->savageScreen->frontOffset>>11;
 	break;
-    case BUFFER_BIT_BACK_LEFT:
+    case BUFFER_BACK_LEFT:
         imesa->IsDouble = GL_TRUE;
 	imesa->regs.s4.destCtrl.ni.offset = imesa->savageScreen->backOffset>>11;
 	break;
diff --git a/src/mesa/drivers/dri/sis/sis6326_state.c b/src/mesa/drivers/dri/sis/sis6326_state.c
index 08402fb3e2..e47e663c35 100644
--- a/src/mesa/drivers/dri/sis/sis6326_state.c
+++ b/src/mesa/drivers/dri/sis/sis6326_state.c
@@ -497,25 +497,27 @@ void sis6326DDDrawBuffer( GLcontext *ctx, GLenum mode )
    __GLSiSHardware *current = &smesa->current;
 
    if(getenv("SIS_DRAW_FRONT"))
-      ctx->DrawBuffer->_ColorDrawBufferMask[0] = GL_FRONT_LEFT;
+      ctx->DrawBuffer->_ColorDrawBufferIndexes[0] = BUFFER_FRONT_LEFT;
+
+   if (ctx->DrawBuffer->_NumColorDrawBuffers > 1) {
+      FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
 
-   /*
-    * _DrawDestMask is easier to cope with than <mode>.
-    */
    current->hwDstSet &= ~MASK_DstBufferPitch;
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
       current->hwOffsetDest = smesa->front.offset;
       current->hwDstSet |= smesa->front.pitch;
       FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_FALSE );
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       current->hwOffsetDest = smesa->back.offset;
       current->hwDstSet |= smesa->back.pitch;
       FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_FALSE );
       break;
    default:
-      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
       FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_TRUE );
       return;
    }
diff --git a/src/mesa/drivers/dri/sis/sis_state.c b/src/mesa/drivers/dri/sis/sis_state.c
index 33a2f089b8..b7454d4a07 100644
--- a/src/mesa/drivers/dri/sis/sis_state.c
+++ b/src/mesa/drivers/dri/sis/sis_state.c
@@ -547,23 +547,24 @@ void sisDDDrawBuffer( GLcontext *ctx, GLenum mode )
    __GLSiSHardware *prev = &smesa->prev;
    __GLSiSHardware *current = &smesa->current;
 
-   /*
-    * _DrawDestMask is easier to cope with than <mode>.
-    */
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+      FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
+
    current->hwDstSet &= ~MASK_DstBufferPitch;
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
       FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_FALSE );
       current->hwOffsetDest = smesa->front.offset >> 1;
       current->hwDstSet |= smesa->front.pitch >> 2;
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_FALSE );
       current->hwOffsetDest = smesa->back.offset >> 1;
       current->hwDstSet |= smesa->back.pitch >> 2;
       break;
    default:
-      /* GL_NONE or GL_FRONT_AND_BACK or stereo left&right, etc */
       FALLBACK( smesa, SIS_FALLBACK_DRAW_BUFFER, GL_TRUE );
       return;
    }
diff --git a/src/mesa/drivers/dri/sis/sis_tris.c b/src/mesa/drivers/dri/sis/sis_tris.c
index a0e39dcd3c..adbbb8ae13 100644
--- a/src/mesa/drivers/dri/sis/sis_tris.c
+++ b/src/mesa/drivers/dri/sis/sis_tris.c
@@ -848,7 +848,7 @@ static void sisRenderStart( GLcontext *ctx )
 
    RENDERINPUTS_COPY( index_bitset, tnl->render_inputs_bitset );
 
-   if (ctx->DrawBuffer->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT && 
+   if (ctx->DrawBuffer->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT && 
       smesa->driDrawable->numClipRects != 0)
    {
       multipass_cliprect(ctx, 0);
diff --git a/src/mesa/drivers/dri/tdfx/tdfx_render.c b/src/mesa/drivers/dri/tdfx/tdfx_render.c
index f36c97bfeb..7b3ce36d1b 100644
--- a/src/mesa/drivers/dri/tdfx/tdfx_render.c
+++ b/src/mesa/drivers/dri/tdfx/tdfx_render.c
@@ -275,7 +275,7 @@ static void tdfxClear( GLcontext *ctx, GLbitfield mask )
                                         fxMesa->Color.ClearAlpha,
                                         fxMesa->Depth.Clear);
 	 FX_grColorMaskv_NoLock(ctx, true4);
-	 if (ctx->DrawBuffer->_ColorDrawBufferMask[0] & BUFFER_BIT_FRONT_LEFT)
+	 if (ctx->DrawBuffer->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT)
             fxMesa->Glide.grRenderBuffer(GR_BUFFER_FRONTBUFFER);
 	 if (!ctx->Depth.Test || !ctx->Depth.Mask)
 	    fxMesa->Glide.grDepthMask(FXFALSE);
@@ -295,7 +295,7 @@ static void tdfxClear( GLcontext *ctx, GLbitfield mask )
                fxMesa->Glide.grDepthMask(FXTRUE);
             }
             FX_grColorMaskv_NoLock(ctx, true4);
-            if (ctx->DrawBuffer->_ColorDrawBufferMask[0] & BUFFER_BIT_FRONT_LEFT)
+            if (ctx->DrawBuffer->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT)
                fxMesa->Glide.grRenderBuffer(GR_BUFFER_FRONTBUFFER);
          }
       }
diff --git a/src/mesa/drivers/dri/tdfx/tdfx_state.c b/src/mesa/drivers/dri/tdfx/tdfx_state.c
index 42cb5dfaa3..e4d77e6742 100644
--- a/src/mesa/drivers/dri/tdfx/tdfx_state.c
+++ b/src/mesa/drivers/dri/tdfx/tdfx_state.c
@@ -1033,21 +1033,23 @@ static void tdfxDDDrawBuffer( GLcontext *ctx, GLenum mode )
 
    FLUSH_BATCH( fxMesa );
 
-   /*
-    * _ColorDrawBufferMask is easier to cope with than <mode>.
-    */
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers > 1) {
+      FALLBACK( fxMesa, TDFX_FALLBACK_DRAW_BUFFER, GL_TRUE );
+      return;
+   }
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
       fxMesa->DrawBuffer = fxMesa->ReadBuffer = GR_BUFFER_FRONTBUFFER;
       fxMesa->new_state |= TDFX_NEW_RENDER;
       FALLBACK( fxMesa, TDFX_FALLBACK_DRAW_BUFFER, GL_FALSE );
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       fxMesa->DrawBuffer = fxMesa->ReadBuffer = GR_BUFFER_BACKBUFFER;
       fxMesa->new_state |= TDFX_NEW_RENDER;
       FALLBACK( fxMesa, TDFX_FALLBACK_DRAW_BUFFER, GL_FALSE );
       break;
-   case 0:
+   case -1:
       FX_grColorMaskv( ctx, false4 );
       FALLBACK( fxMesa, TDFX_FALLBACK_DRAW_BUFFER, GL_FALSE );
       break;
diff --git a/src/mesa/drivers/dri/unichrome/via_context.c b/src/mesa/drivers/dri/unichrome/via_context.c
index 1551be5e75..a06b65224d 100644
--- a/src/mesa/drivers/dri/unichrome/via_context.c
+++ b/src/mesa/drivers/dri/unichrome/via_context.c
@@ -736,8 +736,8 @@ void viaXMesaWindowMoved(struct via_context *vmesa)
    draw_buffer =  (struct via_renderbuffer *) drawable->driverPrivate;
    read_buffer =  (struct via_renderbuffer *) readable->driverPrivate;
    
-   switch (vmesa->glCtx->DrawBuffer->_ColorDrawBufferMask[0]) {
-   case BUFFER_BIT_BACK_LEFT: 
+   switch (vmesa->glCtx->DrawBuffer->_ColorDrawBufferIndexes[0]) {
+   case BUFFER_BACK_LEFT: 
       if (drawable->numBackClipRects == 0) {
 	 vmesa->numClipRects = drawable->numClipRects;
 	 vmesa->pClipRects = drawable->pClipRects;
@@ -747,7 +747,7 @@ void viaXMesaWindowMoved(struct via_context *vmesa)
 	 vmesa->pClipRects = drawable->pBackClipRects;
       }
       break;
-   case BUFFER_BIT_FRONT_LEFT:
+   case BUFFER_FRONT_LEFT:
       vmesa->numClipRects = drawable->numClipRects;
       vmesa->pClipRects = drawable->pClipRects;
       break;
diff --git a/src/mesa/drivers/dri/unichrome/via_state.c b/src/mesa/drivers/dri/unichrome/via_state.c
index bccdbe9326..d2c528923f 100644
--- a/src/mesa/drivers/dri/unichrome/via_state.c
+++ b/src/mesa/drivers/dri/unichrome/via_state.c
@@ -656,13 +656,18 @@ static void viaDrawBuffer(GLcontext *ctx, GLenum mode)
    if (!ctx->DrawBuffer)
       return;
 
-   switch ( ctx->DrawBuffer->_ColorDrawBufferMask[0] ) {
-   case BUFFER_BIT_FRONT_LEFT:
+   if (ctx->DrawBuffer->_NumColorDrawBuffers != 1) {
+      FALLBACK(vmesa, VIA_FALLBACK_DRAW_BUFFER, GL_TRUE);
+      return;
+   }
+
+   switch ( ctx->DrawBuffer->_ColorDrawBufferIndexes[0] ) {
+   case BUFFER_FRONT_LEFT:
       VIA_FLUSH_DMA(vmesa);
       vmesa->drawBuffer = &vmesa->front;
       FALLBACK(vmesa, VIA_FALLBACK_DRAW_BUFFER, GL_FALSE);
       break;
-   case BUFFER_BIT_BACK_LEFT:
+   case BUFFER_BACK_LEFT:
       VIA_FLUSH_DMA(vmesa);
       vmesa->drawBuffer = &vmesa->back;
       FALLBACK(vmesa, VIA_FALLBACK_DRAW_BUFFER, GL_FALSE);
diff --git a/src/mesa/drivers/glide/fxdd.c b/src/mesa/drivers/glide/fxdd.c
index 4e56f7bde5..c082fd827f 100644
--- a/src/mesa/drivers/glide/fxdd.c
+++ b/src/mesa/drivers/glide/fxdd.c
@@ -1955,8 +1955,8 @@ fx_check_IsInHardware(GLcontext * ctx)
       return FX_FALLBACK_STENCIL;
    }
 
-   if (ctx->DrawBuffer->_ColorDrawBufferMask[0] != BUFFER_BIT_FRONT_LEFT &&
-       ctx->DrawBuffer->_ColorDrawBufferMask[0] != BUFFER_BIT_BACK_LEFT) {
+   if ((ctx->DrawBuffer->_ColorDrawBufferIndexes[0] != BUFFER_BIT_FRONT_LEFT) &&
+       (ctx->DrawBuffer->_ColorDrawBufferIndexes[0] != BUFFER_BIT_BACK_LEFT)) {
       return FX_FALLBACK_DRAW_BUFFER;
    }
 
diff --git a/src/mesa/drivers/x11/xm_line.c b/src/mesa/drivers/x11/xm_line.c
index 7109c43915..9833b4c9f0 100644
--- a/src/mesa/drivers/x11/xm_line.c
+++ b/src/mesa/drivers/x11/xm_line.c
@@ -587,8 +587,8 @@ get_line_func(GLcontext *ctx)
    const int depth = GET_VISUAL_DEPTH(xmesa->xm_visual);
    const struct xmesa_renderbuffer *xrb;
 
-   if ((ctx->DrawBuffer->_ColorDrawBufferMask[0]
-        & (BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT)) == 0)
+   if ((ctx->DrawBuffer->_ColorDrawBufferIndexes[0] != BUFFER_BIT_FRONT_LEFT) &&
+       (ctx->DrawBuffer->_ColorDrawBufferIndexes[0] != BUFFER_BIT_BACK_LEFT))
       return (swrast_line_func) NULL;
    if (ctx->RenderMode != GL_RENDER)      return (swrast_line_func) NULL;
    if (ctx->Line.SmoothFlag)              return (swrast_line_func) NULL;
@@ -662,7 +662,7 @@ get_line_func(GLcontext *ctx)
 
 #ifndef XFree86Server
    if (ctx->DrawBuffer->_NumColorDrawBuffers == 1
-       && ctx->DrawBuffer->_ColorDrawBufferMask[0] == BUFFER_BIT_FRONT_LEFT
+       && ctx->DrawBuffer->_ColorDrawBufferIndexes[0] == BUFFER_FRONT_LEFT
        && swrast->_RasterMask == LOGIC_OP_BIT
        && ctx->Color.LogicOp == GL_XOR
        && !ctx->Line.StippleFlag
diff --git a/src/mesa/drivers/x11/xm_tri.c b/src/mesa/drivers/x11/xm_tri.c
index a3978abdd0..c87a293756 100644
--- a/src/mesa/drivers/x11/xm_tri.c
+++ b/src/mesa/drivers/x11/xm_tri.c
@@ -1462,8 +1462,8 @@ get_triangle_func(GLcontext *ctx)
 #endif
 
    /* trivial fallback tests */
-   if ((ctx->DrawBuffer->_ColorDrawBufferMask[0]
-        & (BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT)) == 0)
+   if ((ctx->DrawBuffer->_ColorDrawBufferIndexes[0] != BUFFER_BIT_FRONT_LEFT) &&
+       (ctx->DrawBuffer->_ColorDrawBufferIndexes[0] != BUFFER_BIT_BACK_LEFT))
       return (swrast_tri_func) NULL;
    if (ctx->RenderMode != GL_RENDER)
       return (swrast_tri_func) NULL;
diff --git a/src/mesa/main/buffers.c b/src/mesa/main/buffers.c
index 2252bbd4c5..2099977291 100644
--- a/src/mesa/main/buffers.c
+++ b/src/mesa/main/buffers.c
@@ -159,7 +159,10 @@ _mesa_Clear( GLbitfield mask )
        */
       bufferMask = 0;
       if (mask & GL_COLOR_BUFFER_BIT) {
-         bufferMask |= ctx->DrawBuffer->_ColorDrawBufferMask[0];
+         GLuint i;
+         for (i = 0; i < ctx->DrawBuffer->_NumColorDrawBuffers; i++) {
+            bufferMask |= (1 << ctx->DrawBuffer->_ColorDrawBufferIndexes[i]);
+         }
       }
 
       if ((mask & GL_DEPTH_BUFFER_BIT)
@@ -487,41 +490,6 @@ _mesa_DrawBuffersARB(GLsizei n, const GLenum *buffers)
 
 
 /**
- * Set color output state.  Traditionally, there was only one color
- * output, but fragment programs can now have several distinct color
- * outputs (see GL_ARB_draw_buffers).  This function sets the state
- * for one such color output.
- * \param ctx  current context
- * \param output  which fragment program output
- * \param buffer  buffer to write to (like GL_LEFT)
- * \param destMask  BUFFER_* bitmask
- *                  (like BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_BACK_LEFT).
- */
-static void
-set_color_output(GLcontext *ctx, GLuint output, GLenum buffer,
-                 GLbitfield destMask)
-{
-   struct gl_framebuffer *fb = ctx->DrawBuffer;
-
-   ASSERT(output < ctx->Const.MaxDrawBuffers);
-
-   /* Set per-FBO state */
-   fb->ColorDrawBuffer[output] = buffer;
-   fb->_ColorDrawBufferMask[output] = destMask;
-
-   /* this will be computed later, but zero to be safe */
-   fb->_NumColorDrawBuffers = 0;
-
-   if (fb->Name == 0) {
-      /* Only set the per-context DrawBuffer state if we're currently
-       * drawing to a window system framebuffer.
-       */
-      ctx->Color.DrawBuffer[output] = buffer;
-   }
-}
-
-
-/**
  * Helper function to set the GL_DRAW_BUFFER state in the context and
  * current FBO.
  *
@@ -531,7 +499,7 @@ set_color_output(GLcontext *ctx, GLuint output, GLenum buffer,
  * \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_* bitmasks which correspond to the
+ * \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).
  */
@@ -539,13 +507,13 @@ void
 _mesa_drawbuffers(GLcontext *ctx, GLuint n, const GLenum *buffers,
                   const GLbitfield *destMask)
 {
+   struct gl_framebuffer *fb = ctx->DrawBuffer;
    GLbitfield mask[MAX_DRAW_BUFFERS];
-   GLuint output;
 
    if (!destMask) {
       /* compute destMask values now */
-      const GLbitfield supportedMask
-         = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
+      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);
@@ -554,13 +522,44 @@ _mesa_drawbuffers(GLcontext *ctx, GLuint n, const GLenum *buffers,
       destMask = mask;
    }
 
-   for (output = 0; output < n; output++) {
-      set_color_output(ctx, output, buffers[output], destMask[output]);
+   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 {
+      GLuint buf, count = 0;
+      for (buf = 0; buf < n; buf++ ) {
+         if (destMask[buf]) {
+            fb->_ColorDrawBufferIndexes[buf] = _mesa_ffs(destMask[buf]) - 1;
+            count = buf + 1;
+         }
+         else {
+            fb->_ColorDrawBufferIndexes[buf] = -1;
+         }
+      }
+      /* set remaining outputs to -1 (GL_NONE) */
+      while (buf < ctx->Const.MaxDrawBuffers) {
+         fb->_ColorDrawBufferIndexes[buf] = -1;
+         buf++;
+      }
+      fb->_NumColorDrawBuffers = count;
    }
 
-   /* set remaining color outputs to NONE */
-   for (output = n; output < ctx->Const.MaxDrawBuffers; output++) {
-      set_color_output(ctx, output, GL_NONE, 0x0);
+   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->NewState |= _NEW_COLOR;
diff --git a/src/mesa/main/framebuffer.c b/src/mesa/main/framebuffer.c
index 8f92fd3b42..06a3457488 100644
--- a/src/mesa/main/framebuffer.c
+++ b/src/mesa/main/framebuffer.c
@@ -109,8 +109,9 @@ _mesa_new_framebuffer(GLcontext *ctx, GLuint name)
    if (fb) {
       fb->Name = name;
       fb->RefCount = 1;
+      fb->_NumColorDrawBuffers = 1;
       fb->ColorDrawBuffer[0] = GL_COLOR_ATTACHMENT0_EXT;
-      fb->_ColorDrawBufferMask[0] = BUFFER_BIT_COLOR0;
+      fb->_ColorDrawBufferIndexes[0] = BUFFER_COLOR0;
       fb->ColorReadBuffer = GL_COLOR_ATTACHMENT0_EXT;
       fb->_ColorReadBufferIndex = BUFFER_COLOR0;
       fb->Delete = _mesa_destroy_framebuffer;
@@ -141,14 +142,16 @@ _mesa_initialize_framebuffer(struct gl_framebuffer *fb, const GLvisual *visual)
 
    /* Init read/draw renderbuffer state */
    if (visual->doubleBufferMode) {
+      fb->_NumColorDrawBuffers = 1;
       fb->ColorDrawBuffer[0] = GL_BACK;
-      fb->_ColorDrawBufferMask[0] = BUFFER_BIT_BACK_LEFT;
+      fb->_ColorDrawBufferIndexes[0] = BUFFER_BACK_LEFT;
       fb->ColorReadBuffer = GL_BACK;
       fb->_ColorReadBufferIndex = BUFFER_BACK_LEFT;
    }
    else {
+      fb->_NumColorDrawBuffers = 1;
       fb->ColorDrawBuffer[0] = GL_FRONT;
-      fb->_ColorDrawBufferMask[0] = BUFFER_BIT_FRONT_LEFT;
+      fb->_ColorDrawBufferIndexes[0] = BUFFER_FRONT_LEFT;
       fb->ColorReadBuffer = GL_FRONT;
       fb->_ColorReadBufferIndex = BUFFER_FRONT_LEFT;
    }
@@ -636,39 +639,17 @@ _mesa_update_stencil_buffer(GLcontext *ctx,
 static void
 update_color_draw_buffers(GLcontext *ctx, struct gl_framebuffer *fb)
 {
-   GLuint output, count = 0;
+   GLuint output;
 
-   /* First, interpret _ColorDrawBufferMask[] in the manner that would be
-    * used if the fragment program/shader writes to gl_FragData[]
-    */
-   for (output = 0; output < ctx->Const.MaxDrawBuffers; output++) {
-      GLuint buf = _mesa_ffs(fb->_ColorDrawBufferMask[output]);
-      if (buf) {
-         struct gl_renderbuffer *rb = fb->Attachment[buf - 1].Renderbuffer;
-         fb->_ColorDrawBuffers[output] = rb; /* may be NULL */
-         if (rb)
-            count = output + 1;
+   for (output = 0; output < fb->_NumColorDrawBuffers; output++) {
+      GLint buf = fb->_ColorDrawBufferIndexes[output];
+      if (buf >= 0) {
+         fb->_ColorDrawBuffers[output] = fb->Attachment[buf].Renderbuffer;
       }
-   }
-
-   /* Second, handle the GL_FRONT_AND_BACK case, overwriting the above
-    * if needed.
-    */
-   GLbitfield bufferMask = fb->_ColorDrawBufferMask[0];
-   if (_mesa_bitcount(bufferMask) > 1) {
-      GLuint i;
-      count = 0;
-      for (i = 0; bufferMask && i < BUFFER_COUNT; i++) {
-         if (bufferMask & (1 << i)) {
-            struct gl_renderbuffer *rb = fb->Attachment[i].Renderbuffer;
-            fb->_ColorDrawBuffers[count] = rb;
-            count++;
-         }
-         bufferMask &= ~(1 << i);
+      else {
+         fb->_ColorDrawBuffers[output] = NULL;
       }
    }
-                               
-   fb->_NumColorDrawBuffers = count;
 }
 
 
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 0e7364c08f..c8718a7f63 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -2395,12 +2395,10 @@ struct gl_framebuffer
    GLenum ColorDrawBuffer[MAX_DRAW_BUFFERS];
    GLenum ColorReadBuffer;
 
-   /* These are computed from ColorDrawBuffer and ColorReadBuffer */
-   GLbitfield _ColorDrawBufferMask[MAX_DRAW_BUFFERS]; /* Mask of BUFFER_BIT_* flags */
-   GLint _ColorReadBufferIndex; /* -1 = None */
-
-   /* These are computed from _ColorDrawBufferMask and _ColorReadBufferIndex */
+   /** Computed from ColorDraw/ReadBuffer above */
    GLuint _NumColorDrawBuffers;
+   GLint _ColorDrawBufferIndexes[MAX_DRAW_BUFFERS]; /**< BUFFER_x or -1 */
+   GLint _ColorReadBufferIndex; /* -1 = None */
    struct gl_renderbuffer *_ColorDrawBuffers[MAX_DRAW_BUFFERS];
    struct gl_renderbuffer *_ColorReadBuffer;