Next: CLIM drawing functions, Previous: Concepts, Up: Top
A typical windowing system provides a hierarchy of rectangular areas called windows. When a drawing functions is called to draw an object (such as a line or a circle) in a window of such a hierarchy, the arguments to the drawing function will include at least the window and a number of coordinates relative to (usually) the upper left corner of the window.
To translate such a request to the actual altering of pixel values in the video memory, the windowing system must translate the coordinates given as argument to the drawing functions into coordinates relative to the upper left corner of the entire screen. This is done by a composition of translation transformations applied to the initial coordinates. These transformations correspond to the position of each window in the coordinate system of its parent.
Thus a window in such a system is really just some values indicating its height, its width, and its position in the coordinate system of its parent, and of course information about background and foreground colors and such.