Fresco Tutorial
In the last chapter we examined the Fresco architecture and saw how user interface objects can mix arbitrarily with graphical objects (those that perform graphical transformations.) We explored Fresco's use of a standard object model, CORBA, which allows for object distribution and provides a standardized, high-level notation called IDL for object definition. We also looked at some different types of glyphs in Fresco. Recall that viewers are glyphs that handle the user's keyboard and mouse events. A button is an example of a viewer. The button changes color when the mouse is moved on top of it, and it executes an action when the mouse is pressed and released on it.
Besides handling input, viewer objects may also represent logical views in a subject-view relationship. A subject is a piece of data that is observed by one or more views. (For this reason, we often called views observers.) When the subject is changed, its views are notified. This allows each view to be kept visually "in sync" with the subject. In this chapter, we will explore various subject-view relationships. We begin with a very simple example program and then progress to the RGB color editor shown in figure 2-1.
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