When viewing a big slog2 file like the one shown in Figure ,
the whole timeline canvas is filled up with preview drawables. Though
it provides a reasonable description at high level, i.e. one still
gets a vague sense where the long and/or frequent drawables are. Nevertheless,
it is pretty obscure to know the details. Hence, a well-designed zoomable
and scrollable user interface (ZSUI) of the timeline canvas becomes
an absolute necessity to facilitate the location of events of interest.
The ZSUI of the timeline canvas includes many parts and operations.
But the most handy ones are dragged zoom, grasp and scroll
and instant zoom in and out.All these features are supported
by the Zoomable and Scrollable canvas. There are 2 such canvases in
the Timeline window. They are Timeline Canvas and Time
Ruler Canvas. In these canvases, left mouse clicking can be alternated
in 2 different modes by a pair of toggled buttons as shown in Figures
and
. They are
called Zoom and Hand modes. Each canvas in the Timeline
window has its own set of toggled buttons that determine its left
mouse click behavior. The timeline canvas's toggled buttons are located
above the canvas and sit at the end of the time display panel. The
time ruler's toggled buttons are located at the bottom of row adjustment
panel, i.e. sit right next to the end of the ruler. By default, the
timeline canvas is in zoom mode and the time ruler canvas is in hand
mode, so user can do zooming when the cursor is in the timeline canvas
and can scroll easily by simply moving the cursor over the ruler canvas.
Also, the scrolling can be done by simply dragging on scrollbar's
knob, clicking the end buttons and in the space between the knob and
scrollbar's end buttons.