Appendix A of the Ceder Chest of C1 and C2. The material is copyrighted, so please treat it accordingly.

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A Shape Changer is any call in which the floor spots occupied by dancers at the beginning of the call are different than the floor spots occupied by dancers at the end of the call. In other words, the geometric shape of the formation has changed either by rotating 90° or by evolving into a different formation. For the purposes of this appendix, we will only discuss calls done from 2x4s that are offset by 50% which, after execution, rotate the original starting footprints by 90°.

When dancing calls without Phantoms from setups that are not offset, one does not need to concern oneself with the Shape Changing aspect of a call; however, when dancing Shape Changers from a Parallelogram or Offset 2x4, this becomes a very important aspect indeed. When doing a non-Shape Changing call from an offset setup, you re-establish the exact footprints on the floor at the conclusion of the call that you had at the beginning of the call. With a Shape Changer, however, re-establishing footprints to the exact starting formation is not possible, but establishing relative footprints in a complementary formation is possible, and a method for doing so is described below.

There are two parameters to remember when dealing with any offset formation:

1. The Shear Line is the imaginary line which evenly divides the formation into two halves, and along which exactly half of the dancers have been shifted 50% relative to the other half of the dancers. Assuming that you are Squared off to the walls and that the caller is at the North or South end of the hall, the Shear Line is either a North-South dividing line (henceforth called a Head Shear since it bisects the square through the Heads initial starting position), or an East-West dividing line (henceforth called a Side Shear since it bisects the square through the Sides initial starting position). Note that the Shear Line always passes through the very Center of the set.
2. The Shift Direction is the direction along the Shear Line in which the dancers have been shifted. The Shift Direction is either Clockwise (CW) or Counter-Clockwise (CCW). Note that "Right" or "Left" or "Up" or "Down" would be insufficient information, since exactly half the dancers would be shifted in one direction (e.g., "Right") while their opposite dancers would be shifted in the opposite direction (e.g., "Left"). Right-Left fails to clarify which half of the square is shifted in which direction (i.e., is the top half shifted Right, or is the bottom half shifted Right?). CW and CCW, on the other hand, indicate the Shift Direction of both halves of the square at the same time. To determine whether the Shift Direction is CW or CCW, imagine grabbing the dancers on one side of the Shear Line with one hand and grabbing the dancers on the other side of the Shear Line with your other hand, almost like holding a steering wheel. Now, imagine simultaneously moving both halves of the square along the Shear Line in the direction of the offset, one hand in one direction and the other hand in the opposite direction. If you turn the "steering wheel" to the right, the Shift Direction is Clockwise (CW); if you turn the "steering wheel" to the Left, the Shift Direction is Counter-Clockwise (CCW).

To dance Shape Changers from offset formations, you must determine the Shear Line and Shift Direction of the starting formation, execute the call given, and then make sure that you re-establish the same Shear Line and the same Shift Direction in your ending formation.

Diagrammed below are the four possible combinations of Shear Lines and Shift Directions from a Parallelogram (diagram on the left) and the complementary 3x4 Matrix Offset setup (diagram on the right).

(1a) Side Shear CCW   (1b) Side Shear CCW	(2a) Side Shear CW   (2b) Side Shear CW
(3a) Head Shear CCW   (3b) Head Shear CCW	(4a) Head Shear CW   (4b) Head Shear CW

If you start a call from formation (1a) or (1b), you must end in either formation (1a) or (1b). If the call is a shape-changer you will end in the complementary formation 1a -> 1b or 1b -> 1a; if the call is not a shape-changer you will end in the same formation 1a -> 1a or 1b -> 1b. If you start from (2a) or (2b), you must end in (2a) or (2b). Similarly with (3a) and (3b), and also with (4a) and (4b).

This is the non-offset starting formation corresponding to the 4 examples given below.   after Recycle
(1) Side Shear CCW:     before Parallelogram Recycle   after	(2) Side Shear CW:     before Parallelogram Recycle   after
(3) Head Shear CCW:     before Offset Waves Recycle   after	(4) Head Shear CW:     before Offset Waves Recycle   after