You may shift the red, yellow and black lines by dragging white points A, B and C,
and rotate these lines around their white points, and so set the positions of
invariant points X and Y.
The invariants may be sent as
far out of view as is altogether possible, one at a time, or together,
or they may be set in view, one at a time, or together. Please do note carefully
that this requires rotation of lines, not translation. Lines cannot
translate. (See a formal list of changes.)
Change the intervals by dragging D and/or U,
and shift the entire set of them using the yellow point.