A Simple Screen Reader

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To illustrate the use of the UNO accessibility API, we will describe how to implement a simple AT. The simple screen reader, or SSR, will display some information about the currently focused object. As you can see in Illustration 18.1, the SSR consists of three windows. The bottom window logs all events that the SSR receives from any of the accessibility objects to which it is registered.

The simple screen reader shows information on the currently focused object in two different views. A textual display on the top left shows its description, states and bounding box as well as the names of its ancestors. The graphical view on the top right shows the bounding boxes of the object itself (green) and its ancestors (gray). The bottom window logs all events sent by any of the accessibility objects.

The two upper windows display information about the currently focused object, which in this screen shot is a shape in a presentation document. The left window displays the names of all the ancestors of the focused object and the path from that object to the root object of the accessibility tree. The left window also displays the focused object's description, its state, its location, and its size on the screen. In this example, the focused object is named “Rectangle2”, which corresponds to the red rectangular shape. Its parent is called “Drawing View” and the root of the tree has the name of the document, which is “Untitled1”, followed by the product name and some debug information.

The upper right window displays similar information graphically. The focused object is shown as a green rectangle, while its ancestors are drawn as gray rectangles. You can see how the objects are nested. This corresponds to the requirement that the bounding of child objects must not overlap that of their parents. Note that the blue rectangular shape is not visible in this window, because it is a sibling of the focused red rectangle, but does not lie on that object's path to the root of the root object. Also note that some of the rectangles are off-center and smaller than they should be. This is because the rectangles that represent accessible objects, which in turn represent part of the GUI, are drawn with their screen location and size relative to the whole screen; the outermost rectangle that is enclosed by the gray background represents the screen of which the screen shot shows only a part.

The bottom window logs all the events that the SSR receives from the accessible objects it has register as event listener at.

Content on this page is licensed under the Public Documentation License (PDL).
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