Clarify the convention on modifiers and drags.

diff --git a/gtk2_ardour/editor_drag.cc b/gtk2_ardour/editor_drag.cc
index f9222ac35adba9b1fbf2833276d316ef42104159..00811f6eea72bedaa88648e5e2e9fcd8a931b816 100644 (file)
--- a/gtk2_ardour/editor_drag.cc
+++ b/gtk2_ardour/editor_drag.cc
@@ -404,6 +404,11 @@ Drag::motion_handler (GdkEvent* event, bool from_autoscroll)
                                } else {
                                        _initially_vertical = false;
                                }
+                               /** check constraints for this drag.
+                                *  Note that the current convention is to use "contains" for 
+                                *  key modifiers during motion and "equals" when initiating a drag.
+                                *  In this case we haven't moved yet, so "equals" applies here.
+                                */
                                if (Config->get_edit_mode() != Lock) {
                                        if (event->motion.state & Gdk::BUTTON2_MASK) {
                                                // if dragging with button2, the motion is x constrained, with constraint modifier it is y constrained