It is often useful to be able to record the steps involved in a construction for playback later. Geometry Explorer provides this capability through the use of a Recorder window. This can be brought up by choosing "New Recording" under the File menu of the main Geometry Explorer window. Below is a screen capture of a recording of the equilateral triangle construction from Euclid's The Elements.
Recording: To record this construction we first clicked on the "Record" button in the Recorder window and then carried out the steps to create an equilateral triangle. As we construct the triangle, the recorder "listens" in and records each step of the process. It also differentiates between geometric objects that are created and those that are constructed from other objects already existing. For example, the first step in the construction is to draw a circle defined by two points (in this case points A and B). These are recorded as the Basis for the construction since they are not built from already defined objects. The circle is then listed under Construction step (0) as it is built from points A and B which already exist. The next step in the construction is to draw another circle with center equal to the radius point of the first circle and radius point equal to the center point of the first circle. Again, this is built from already existing objects and thus is listed as step (1). We continue with the construction until the triangle is built. At that point we click the "Stop" button to finish the recording.
Playback: To playback a recording we must first select a set of basis elements which exactly match the basis that was recorded. Thus, we must first select two points that will serve as a new basis for the construction described above of an equilateral triangle. If we have selected the right number and type of points for playback, the "Step", "Play", and "FF" (fast forward) buttons will be enabled. Clicking on any of these will start the playback of the recorded construction. The Step function carries out one step in the construction. To execute the next step the "Step" button must be clicked again. The Play function carries out each step of the construction and highlights the corresponding step in the Recorder window as it continues. The FF function (attempts) to carry out the steps in the construction rapidly. At any point in the playback of a construction the "Stop" button can be clicked to stop the playback.
Multiple sets of Basis Objects: In the Recorder window there is a menu titled "Basis". Basis elements are geometric objects that are of the same type as the objects that appear in the "Basis for construction" area in the Recorder text panel. That is, basic objects are the objects that one selects to enable playback of a recording. Often it is useful to playback a recording on more than one group of such objects. We do this by storing away each set of basis objects. For example, in the recording above, the basis set is the set of two points {A,B}. To store multiple sets of basis objects we first select two points (as a basis set) and then choose "Store Givens Set" under the Basis menu. Then, we can select another set of two points and store these. We continue until we have stored as many sets of basis objects as we desire. Then, when the recording is played back, it will be played back on each set of basis objects in sequence.
Looping: Recursive constructions can be recorded by using the "Loop" feature. With this feature we can set a set of objects as basis objects in a recording while we are doing the recording. One good example of this capability is found in the construction of the Koch Snowflake curve.