under construction
Introduction
IGB's modified MVC architecture in theory should allow us to present many diverse views of data to users. However, this built-in flexibility has been hard to exploit because of complexities in TierGlyph classes that render and represent data.
In this document, we'll describe some of problems users confront when interacting with data tracks and offer some ideas for how these interactions could improve.
The Rubber Canvas
IGB implements a one-dimensional variant of animated, semantic zooming, in which objects and the data field appear to stretch or contract about a central line (the zoom stripe) during zooming and objects show more detail as users zoom in for a closer look.
In IGB, one-dimensional horizontal and vertical zooming happen independently of each other, reflecting the one-dimensional nature of sequence data and associated annotations. This differs from how zooming works in camera-zooming applications (e.g., Adobe Acrobat) where zooming mimics the action of a camera rising or descending over a two-dimensional field of data.
In IGB, the process of zooming is more like pulling on both sides of canvas with equal force, where the canvas has a central stripe that remains in place as it stretches on either side. (Once this central stripe was called the "Hairline;" more recent versions of IGB use the term "zoom stripe.")
Horizontal zooming tends to work very well for users; they seem to instantly grasp how zooming focus works: Clicking a position in the display focuses zooming and operating the horizontal slider zooms in or out. We've also implemented double-clicking to zoom in on a feature and click-drag across the coordinate axis to zoom in a selected region.
However, it has been harder to communicate the idea of how vertical zooming works, which, in IGB, is more like a vertical stretch rather than a zoom in the usual sense of the word. To zoom vertically, a user operates the vertical slide on the left side of the main display window. Dragging the thumb stretches the display vertically, with the position of the user's last click staying more or less in view while the rest of the display stretches around it.
This works relatively well, once the user grasps that vertical zooming happens about a horizontal line, which is invisible.
(Note: Adding a cross-hair to the Zoom Stripe may help users master this interaction more quickly.)
Better vertical stretch
The vertical coordinate system in IGB does not have the same meaning as the horizontal coordinates system, which is closely wedded to the sequence data itself. This means that we have near total freedom over how we use vertical layout to convey information and help