class MouseSource

A method for a client to receive mouse pointer events.

The position of a pointer event is defined in the context of a viewport,

situated in the view. The dimensions of the view and viewport, and their

spatial relationship (defined with a transform matrix), are supplied

synchronously in a |ViewParameter| table. A view may retrieve a pointer's

position in its local coordinate system by applying the viewport-to-view

transform matrix.

The viewport is embedded in an independent and stable coordinate system,

suitable for interpreting pointer events in a scale-independent manner;

mouse movement will be observed at a constant scale, even under effects such

as magnification or panning. However, other effects, such as enlargening the

view's clip bounds, may trigger a change in the viewport extents.