Wednesday, January 18, 2012

Multitouch Gestures in the Generic Graph View

In my previous post, I've already described the discovery mechanisms of the Generic Graphical View project: Starting from one node you can step by step reveal other connected nodes in the same model. The model itself is fixed - it is still a view! - but the user can decide herself which subset of elements should appear in the diagram. That behavor allows to create diagram views focussed on a specific semantic aspect of the model.

The challenge is to find a decent UI for nodes wich have several hidden connections. How should a user select any subset of these?

Since the Helios release SWT supports four multitouch gestures: PAN, ZOOM, SWIPE and ROTATE. On my Mac's touchpad these gestures are actually easier to perform than a conventional drag operation because there is no extra mouse button. So I decided to give it a try and have a look how gestures could be used in the graph view. Here is a screencast showing the results:

SWT's multitouch API is fairly simple (example snippet). The first step was to add multitouch events to GEF, such that the can be handled in the same way as mouse or keyboard events. I had to extend a couple of GEF classes. If you're interested in the details, have a look at the classes in the package org.eclipse.xtext.graphview.behavior.gestures and the GraphViewRootEditPart.

These changes allow to use a ZOOM gesture on a ScalableFreeformRootEditPart.
Note that the PAN gesture is already supported by GEF because the FigureCanvas uses hardware scrolling. Unfortunately, these event is always consumed, such that it will not make it through to other GEF elements.

The ZOOM gesture can also be used to drill down into elements. If the mapping defines an open reference to another diagram, you can drill down by selecting it and performing the ZOOM in gesture. If you‘re inside a drill down diagram, you can ZOOM out into the container diagram.

Any Tool can now handle multitouch gestures by implementing the IViewerGestureHandler interface. For a DragTracker this makes no sense, as it is exited as soon as the mouse key is released and you cannot start a drag and a multitouch gesture simultaneously.

The RevealGestureTool works as follows: Click on the + button to reveal the hidden connected elements, Then use ROTATE or SWIPE to rotate elements, ZOOM to change the distance and right-click to select and pin individual elements. Another click will commit the input.