Rework the GL_READ_BUFFER, GL_DRAW_BUFFER state repairs that Roland previously did.

Basically, in update_framebuffer() (which should be called after an FBO is bound
with MakeCurrent or BindFramebuffer) we check if the FBO is a window-system FBO.
If it is, update the FBO's GL_READ/DRAW_BUFFER state according to the context state.
Old code still in place but disabled with #if 0 / #endif.

src/mesa/main/fbobject.c

@@ -962,9 +962,11 @@ _mesa_BindFramebufferEXT(GLenum target, GLuint framebuffer)
    }
 
    FLUSH_VERTICES(ctx, _NEW_BUFFERS);
+
    if (ctx->Driver.Flush) {  
       ctx->Driver.Flush(ctx);
    }
+
    if (framebuffer) {
       /* Binding a user-created framebuffer object */
       newFb = _mesa_lookup_framebuffer(ctx, framebuffer);
@@ -998,34 +1000,43 @@ _mesa_BindFramebufferEXT(GLenum target, GLuint framebuffer)
     * XXX check if re-binding same buffer and skip some of this code.
     */
 
+#if 000
    /* for window-framebuffers, re-initialize the fbo values, as they
       could be wrong (makecurrent with a new drawable while still a fbo
       was bound will lead to default init fbo values).
       note that therefore the context ReadBuffer/DrawBuffer values are not
       valid while fbo's are bound!!! */
+#endif
    if (bindReadBuf) {
       _mesa_reference_framebuffer(&ctx->ReadBuffer, newFbread);
+#if 000
       if (!newFbread->Name) {
          _mesa_readbuffer_update_fields(ctx, ctx->Pixel.ReadBuffer);
       }
+#endif
    }
 
    if (bindDrawBuf) {
       /* check if old FB had any texture attachments */
       check_end_texture_render(ctx, ctx->DrawBuffer);
+
       /* check if time to delete this framebuffer */
       _mesa_reference_framebuffer(&ctx->DrawBuffer, newFb);
-      if (!newFb->Name) {
+
+      if (newFb->Name != 0) {
+         /* check if newly bound framebuffer has any texture attachments */
+         check_begin_texture_render(ctx, newFb);
+      }
+      else {
+         /* XXX try to remove this: */
+#if 000
          GLuint i;
          GLenum buffers[MAX_DRAW_BUFFERS];
          for(i = 0; i < ctx->Const.MaxDrawBuffers; i++) {
             buffers[i] = ctx->Color.DrawBuffer[i];
          }
          _mesa_drawbuffers(ctx, ctx->Const.MaxDrawBuffers, buffers, NULL);
-      }
-      else {
-         /* check if newly bound framebuffer has any texture attachments */
-         check_begin_texture_render(ctx, newFb);
+#endif
       }
    }