> Reinventing The (Square) Wheel Department. > > Problem: given a rectangle ABCD defined by four points on the xy-plane, > detect whether a given point (a mouseclick) falls inside ABCD.
This might help. > Note that side > AB isn't necessarily parallel to the x or y axes. But first you must rotate the rectangle to make its axes parallel to the x and y axis. > Displacement in the xy-plane can't normally be represented by a linear > transformation, but long ago I read of a way of introducing a third virtual z- > axis, which did allow both rotation and displacement to be handled in one > shot by a 3-by-3 matrix. Does anybody know of this technique? I believe you are talking about "affine transformations": http://en.wikipedia.org/wiki/Affine_transformation Have fun :-) -- Stefano [ "Defeat is not the worst of failures. Not to have tried is the true failure." --- George Edward Woodberry ] ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
