A generic graphics package - An Introduction to Graphical User Interfaces with Java Swing - page 256

combineWith , for doing this. This method compares the minima of this and the
DimensionObject given as an argument, and sets the minima to the smaller of
the values. The update of the maxima is done in an analogous way. If a graphical
object is deleted from the drawing the update of extremalDimensions is more dif-
ficult. If one of the values of extremalDimensions , say the minimal x -coordinate,
comes from the deleted object, then one has to find that object of the drawing
that now has minimal x -coordinate. We do this by re-computing the values of ex-
tremalDimensions from scratch. That is, we screen all graphical objects in the
drawing to determine the new extremal values. There are more efficient ways of
updating the values after a deletion but they require elaborate data structures, the
implementation of which would occult the structure of the package.
(a)
(b)
Figure 21.1 The test application GenericDrawingDemo . (a) In proportional mode, i.e. both
coordinate axes have the same scale - circles appear as circles. (b) In non-proportional mode,
i.e. sized to fill the panel - circles might appear as ellipses