In addition, controls that receive user input, such as clickable buttons, typicallyhave their own subwindows. We will keep with this tradition of equating the two terms.1ĬSci493.70 Graphical User Interface ProgrammingDrawing in GTK Prof. All GUI APIs referto the process of visually rendering their windows as painting, or repainting, even if they describe the process occasionally asdrawing.

Drawing is just a special kind of painting.

Technically, the operation we are describing is painting, becauseit is the application of colors and brush strokes to a canvas. For example, a top-levelwindow will typically contain a window for the menu bar, one for the document area, one for each scrollbar,1 Wewill use the terms draw and paint interchangeably. If the user does something that brings Aforward on the screen, then the only region of window A that must be redrawn is the portion of A in thesetA (B C),which is shaded in the gure.Figure 1: Window clipping.Most windowing systems support nested windows, which are calledchild windows.A top-level window maycontain many child windows, which may contain child windows in turn, and so on. In Figure1, window A is below window B, which is below window C. Clipping is the act of removing portions of a window that do not need to be redrawn, or looked atthe other way, it is determining which are the only regions of a window that must be redrawn. An exposure event is simply an event sent from the underlyingwindowing system to a widget to notify it that it must redraw itself.In this context, a 'window' means 'a rectangular region with automatic clipping', not a top-level applicationwindow.

For example, if a window that is stacked below otherwindows gets raised to the top, then a client program has to repaint the area that was previously obscured.When the windowing system asks a client program to redraw part of a window, it sends anexposure eventto the program that contains that window. Gnome or KDE or Explorer,does not automatically save the graphical content of an application's windows instead it asks the applicationitself torepaint 1its windows whenever it is needed. Stewart WeissDrawing in GTK BackgroundIn order to understand how to draw in GTK, you rst have to understand something about how GTK drawswidgets, because how GTK draws widgets has an important role in how you design your drawing application.An understanding of how GTK draws widgets is also required if you ever plan to build your own customwidgets.Windows and ClippingMost windowing systems are designed around the idea that an application's visual display lies within arectangular region on the screen called itswindow.The windowing system, e.g.

CSci493.70 Graphical User Interface ProgrammingDrawing in GTK Prof.

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