Creation of a pendulum with dynamic parameters in Flash - Page 5

ActionScripting

We pass now to the more important part: the engine of the pendulum. All the motion of the pendulum happens through the action, set as "object actions" (i.e. action associated to the movie clip) in the control panel movieclip:

onClipEvent (load) {
  a = 1;
  timesmorz = 0.92;
  maxang = 60;
  n_osc = 1;
  }
  
onClipEvent (enterFrame) {
  setProperty (_root.pend, _rotation, (((Math.sin (n_osc*a))*(Math.pow (timesmorz, a ))))*maxang);
  a = a+0.1;
  }

The action onClipEvent (load){ } is an action that only executes during loading of a movie and therefore is useful, for example, to initialize variables (i.e. to assign them an initial value). In our situation we will initialize four variables: the three variables already considered, with values timesmorz=0.92, maxang=60, n_osc=1, plus a quarter one, a=1, that we are in order to understand why. When we set the values of timesmorz,maxang and n_osc during loading, we makes it possible to display their values in the respective text fields, which are grouped inside the control panel movieclip.

The action onClipEvent (enterFrame){ } instead is an action that executes every time that is entered in a frame, therefore if we set, for example, the movie frame rate to 20 fps, the action comprised between the { } will come executed 20 times in 1 second. Taking advantage of this, it is possible to vary the rotation of the pendulum n times in a second if we set the movie frame rate to n fps.