8.11 DUIM-Gadgets Module

<viewport>

Open abstract instantiable class

Summary

The class of viewports.

Superclasses

<gadget> <single-child-composite-pane>

Init-keywords

horizontal-scroll-bar:

An instance of type false-or(<scroll-bar>). Default value: #f.

vertical-scroll-bar:

An instance of type false-or(<scroll-bar>). Default value: #f.

Library

duim-gadgets

Module

duim-gadgets

Description

The class of viewports. A viewport is a sheet "through" which other sheets are visible; they are used to implement a clipping region for scrolling.

The horizontal-scroll-bar: and vertical-scroll-bar: init-keywords specify whether the viewport has horizontal and vertical scroll bars, respectively.

In most applications, you should not need to use a viewport yourself. However, there are some circumstances in which defining your own viewports is invaluable. In particular, if you need to use a single scroll bar to scroll more than one window at the same time, you should define each window as a viewport, and use the same scroll bar to scroll each window. There are two situations where this behavior is quite common:

In applications which have vertical or horizontal rulers around a document window, such as a drawing application. In this case, the rulers must scroll with the drawing itself.
In applications such as spreadsheets, where row and column headings need to scroll with the document. Note that you may also choose to implement this kind of functionality using a table control.

Operations

viewport-region