Transformations and Clipping
Richard Mitchell · 1991
The diagram package allows the user to enter a diagram interactively. A diagram consists of standard items, such as lines and circles, and other shapes defined by the user, called usershapes, which can be made up of the standard items and other usershapes. An item can be entered anywhere in the diagram, hence it must be possible to position a usershape at any position, size or rotation. If a usershape which contains another shape drawn at 45 degrees, is itself drawn at 90 degrees, then the 'inner' shape must be drawn at 135 degrees. This is best acheived using transformation matrices, which are the first topic of the chapter.