In addition to change the scaling of a 2D plot using the
Frame dialog, a displayed plot containing a frame
item can be rescaled conveniently with the help of the mouse. For this, one
corner of a rectangle has to be defined by pressing the middle mouse button.
Then, by moving the mouse diagonally, a rectangle is drawn. Its final size will
be defined by the point where the mouse button is released. The data space
coordinates of the corners then are rounded using Kpl's autoscale feature to
corresponding scaling values of the frameitem and the display is
updated.
The ranges for the x axes of function and spline child items of the frame are
updated correspondingly; the x step widths are set to 0 (resulting in
automatically dividing the ranges into 100 intervals).
