6 DUIM-Graphics Library
6.1 Overview
The DUIM-Graphics library contains interfaces that define a wide variety drawing operations for use in your GUI applications, as well as two classes. The library contains a single module, duim-graphics, from which all the interfaces described in this chapter are exposed. Section 6.6 on page 404 contains complete reference entries for each exposed interface.
The DUIM graphic drawing model is an idealized model of graphical pictures. The model provides the language that application programs use to describe the intended visual appearance of textual and graphical output. Usually not all of the contents of the screen are described using the graphic drawing model. For example, menus and scroll bars would usually be described in higher-level terms.
An important aspect of the DUIM graphic drawing model is its extreme device independence. The model describes ideal graphical images and ignores limitations of actual graphics devices. One consequence of this is that the actual visual appearance of the screen can only be an approximation of the appearance specified by the model: however, another important consequence of this is that the model is highly portable.
DUIM separates output into two layers:
- 1. A text/graphics layer in which you specify the desired visual appearance independent of device resolution and characteristics
- 2. A rendering layer in which some approximation of the desired visual appearance is created on the device.
Of course application programs can inquire about the device resolution and characteristics if they wish and modify their desired visual appearance on that basis. There is also a third layer above these two layers, the adaptive toolkit layer where one specifies the desired functionality rather than the desired visual appearance.