allow alt-drag on stereo panner to move just one side of the stereo field. this wiggles a bit, possibly because of rounding, and that probably needs to be addressed

git-svn-id: svn://localhost/ardour2/branches/3.0@12500 d708f5d6-7413-0410-9779-e7cbd77b26cf

gtk2_ardour/stereo_panner.cc

@@ -476,35 +476,67 @@ StereoPanner::on_motion_notify_event (GdkEventMotion* ev)
 	if (dragging_left) {
 		delta = -delta;
 	}
-
+	
 	if (dragging_left || dragging_right) {
 
-		/* maintain position as invariant as we change the width */
+		if (Keyboard::modifier_state_contains (ev->state, Keyboard::SecondaryModifier)) {
 
+			/* change width and position in a way that keeps the
+			 * other side in the same place
+			 */
 
-		/* create a detent close to the center */
+			_panner->freeze ();
+			
+			double pv = position_control->get_value();
 
-		if (!detented && fabs (current_width) < 0.02) {
-			detented = true;
-			/* snap to zero */
-			width_control->set_value (0);
-		}
-
-		if (detented) {
-
-			accumulated_delta += delta;
-
-			/* have we pulled far enough to escape ? */
-
-			if (fabs (accumulated_delta) >= 0.025) {
-				width_control->set_value (current_width + accumulated_delta);
-				detented = false;
-				accumulated_delta = false;
+			if (dragging_left) {
+				position_control->set_value (pv - delta);
+			} else {
+				position_control->set_value (pv + delta);
 			}
 
+			if (delta > 0.0) {
+				/* delta is positive, so we're about to
+				   increase the width. But we need to increase it
+				   by twice the required value so that the
+				   other side remains in place when we set
+				   the position as well.
+				*/
+				width_control->set_value (current_width + (delta * 2.0));
+			} else {
+				width_control->set_value (current_width + delta);
+			}
+
+			_panner->thaw ();
+
 		} else {
-			/* width needs to change by 2 * delta because both L & R move */
-			width_control->set_value (current_width + delta * 2);
+
+			/* maintain position as invariant as we change the width */
+			
+			/* create a detent close to the center */
+			
+			if (!detented && fabs (current_width) < 0.02) {
+				detented = true;
+				/* snap to zero */
+				width_control->set_value (0);
+			}
+			
+			if (detented) {
+				
+				accumulated_delta += delta;
+				
+				/* have we pulled far enough to escape ? */
+				
+				if (fabs (accumulated_delta) >= 0.025) {
+					width_control->set_value (current_width + accumulated_delta);
+					detented = false;
+					accumulated_delta = false;
+				}
+				
+			} else {
+				/* width needs to change by 2 * delta because both L & R move */
+				width_control->set_value (current_width + (delta * 2.0));
+			}
 		}
 
 	} else if (dragging_position) {

libs/ardour/ardour/panner.h

@@ -151,6 +151,9 @@ public:
 		return fabs (a.azi - b.azi) < 1.0;
 	}
 
+        virtual void freeze ();
+        virtual void thaw ();
+
 protected:
 	boost::shared_ptr<Pannable> _pannable;
 
@@ -158,6 +161,8 @@ protected:
 	virtual void distribute_one_automated (AudioBuffer&, BufferSet& obufs,
 	                                       framepos_t start, framepos_t end, pframes_t nframes,
 	                                       pan_t** buffers, uint32_t which) = 0;
+
+        int32_t _frozen;
 };
 
 } // namespace

libs/ardour/panner.cc

@@ -118,3 +118,17 @@ Panner::set_state (XMLNode const &, int)
 {
 	return 0;
 }
+
+void
+Panner::freeze ()
+{
+	_frozen++;
+}
+
+void
+Panner::thaw ()
+{
+	if (_frozen > 0.0) {
+		_frozen--;
+	}
+}

libs/panners/2in2out/panner_2in2out.cc

@@ -123,9 +123,22 @@ Panner2in2out::set_width (double p)
         }
 }
 
+void
+Panner2in2out::thaw ()
+{
+	Panner::thaw ();
+	if (_frozen == 0) {
+		update ();
+	}
+}
+
 void
 Panner2in2out::update ()
 {
+	if (_frozen) {
+		return;
+	}
+
         /* it would be very nice to split this out into a virtual function
            that can be accessed from BaseStereoPanner and used in do_distribute_automated().
            

libs/panners/2in2out/panner_2in2out.h

@@ -67,6 +67,7 @@ class Panner2in2out : public Panner
         void update ();
 
 	void reset ();
+        void thaw ();
 
   protected:
 	float left[2];