midi: allow clearing clip from GenericMIDI binding

This commit allows the user to clear clips from the Luppp grid
with a MIDI message. The binding method is very similar to the
existing "grid:event" style, with added to "action" representing
1 for press, and 0 for release, -1 now represents a "clear" event.

As such, the following binding would clear clip track 1, scene 1,
when midi note number 60 had a note on event. Note that the value
for "send" is also set to -1, indicating it is not a send binding.

Active set to -1 indicates that the clip should be cleared:

{
  "action": "grid:event",
  "status": 144,
  "data":    60,
  "track":    1,
  "scene":    1,
  "send":    -1,
  "active":  -1
}

See Github issue #134

src/controller/genericmidi.cxx

@@ -495,10 +495,16 @@ void GenericMIDI::midi(unsigned char* midi)
 				jack->getLogic()->trackJackSendActivate(b->track,b->active);
 				break;
 			case Event::GRID_EVENT:
-				if ( b->active )
+				if ( b->active == 1 ) {
+					/* press */
 					jack->getGridLogic()->pressed( b->track, b->scene );
-				else
+				} else if ( b->active == -1 ) {
+					/* clear */
+					jack->getGridLogic()->clear( b->track, b->scene );
+				} else {
+					/* release */
 					jack->getGridLogic()->released( b->track, b->scene );
+				}
 				break;
 
 			case Event::GRID_SELECT_CLIP_EVENT:

src/eventhandlerdsp.cxx

@@ -176,12 +176,8 @@ void handleDspEvents()
 				if ( availableRead >= sizeof(EventGridState) ) {
 					EventGridState ev;
 					jack_ringbuffer_read( rbToDsp, (char*)&ev, sizeof(EventGridState) );
-					// clear clips in Controllers
-					if ( ev.state == GridLogic::STATE_EMPTY ) {
-						jack->getLooper( ev.track )->getClip( ev.scene )->init();
-						jack->getControllerUpdater()->setTrackSceneProgress(ev.track, ev.scene, 0 );
-						jack->getControllerUpdater()->setSceneState( ev.track, ev.scene, GridLogic::STATE_EMPTY );
-					}
+					if ( ev.state == GridLogic::STATE_EMPTY )
+						jack->getGridLogic()->clear( ev.track, ev.scene );
 				}
 				break;
 			}

src/gridlogic.cxx

@@ -211,6 +211,12 @@ void GridLogic::pressed( int track, int scene )
 	jack->getControllerUpdater()->setSceneState(track, scene, s );
 }
 
+void GridLogic::clear( int track, int scene )
+{
+	jack->getLooper( track )->getClip( scene )->init();
+	jack->getControllerUpdater()->setTrackSceneProgress(track, scene, 0 );
+	jack->getControllerUpdater()->setSceneState( track, scene, GridLogic::STATE_EMPTY );
+}
 
 void GridLogic::released( int track, int scene )
 {

src/gridlogic.hxx

@@ -61,6 +61,9 @@ public:
 	/// button press / click event
 	void pressed( int track, int scene );
 
+	/// clears the clip at this location
+	void clear( int track, int scene );
+
 	/// button release / click-release event
 	void released( int track, int scene );