Zooming, Panning, and Scrolling

Canvas navigation can be divided into two main categories: zooming and scrollbar handling which is managed by the CanvasComponent itself, and panning which is managed by the MoveViewportInputMode.

The scrollable area as well as the zoom can be efficiently limited using a ViewportLimiter as discussed in the section Restricting the Viewport.

Mouse Wheel and Scroll Bars

The GraphComponent provides a number of properties which allow specifying mouse wheel behavior, scroll bar policy, and zoom limits.

mouseWheelBehavior

Whether the mouse wheel is used to zoom or scroll (or both).

mouseWheelZoomFactor

How fast the zoom level changes when the mouse wheel is turned.

mouseWheelScrollFactor

How fast the viewport scrolls when the mouse wheel is turned.

centerZoomEventRecognizer

An event recognizer which determines whether zooming is towards the center of the view or towards the mouse location.

mouseWheelZoomEventRecognizer

An event recognizer which determines whether mouse wheel turns should scroll or zoom. This recognizer is only used if mouseWheelBehavior has both the SCROLL and ZOOM flags.

verticalScrollBarPolicy

horizontalScrollBarPolicy

Whether and when to display vertical and horizontal scroll bars.

minimumZoom

maximumZoom

Minimum and maximum allowed values for the zoom factor.

Panning

Panning, i.e. dragging the visible area with the mouse, is handled by MoveViewportInputMode. This input mode is a child input mode of both GraphEditorInputMode and GraphViewerInputMode.

MoveViewportInputMode allows customization by changing the recognizers for some gestures. This might be of importance to avoid conflicts with input modes which share the same gesture (dragging on an empty canvas), e.g. MarqueeSelectionInputMode or LassoSelectionInputMode.

pressedRecognizer

An event recognizer which returns true if an event is recognized as a valid gesture during viewport movement. This recognizer has to return true for all events during the complete drag gesture.

draggedRecognizer

An event recognizer which returns true if an event is recognized as a drag gesture that actually starts moving the viewport. This is only queried if the pressedRecognizer already returns true.

releasedRecognizer

An event recognizer which returns true if an event is recognized as a valid gesture to finish panning.

MoveViewportInputMode also supports touch gestures. Besides panning its touch support also manages zooming by pinch gestures.

primaryDownRecognizer

An event recognizer which returns true if an event is recognized as a gesture that can start a marquee selection or a pinch zoom, usually the primary touch (i.e. "first finger down").

primaryMoveRecognizer

An event recognizer which returns true if an event is recognized as a drag gesture. The gesture actually starts moving the viewport if no secondary touch device is down, otherwise it starts a pinch zoom gesture. This is only queried if the primaryMoveRecognizer already returns true.

primaryUpRecognizer

An event recognizer which returns true if an event is recognized as a valid gesture to finish panning.

secondaryDownRecognizer

An event recognizer which returns true if an event is recognized as a valid gesture to start the actual pinch zoom, usually the second touch ("second finger down"). secondaryMoveRecognizerAn event recognizer which returns true if an event is recognized as a pinch gesture (if primary touch device is down) or pan (if no primary touch device is down).

secondaryUpRecognizer

An event recognizer which returns true if an event is recognized as a valid gesture to finish pinch zoom or panning if no primary touch is down.