Guide is a special feature that enables you to make user-defined motion paths on which your objects can move during the animation. In regular (guide-free) animation you need to make one keyframe for each change of straight movement; with guide you can just draw wanted path for your object, attach the object to the path and have complicated movement done.
Making a guide
To create a guided object you need to create a layer that will contain your guide-line. First, create one layer which will be designated as guiding layer and one layer that will be designated as guided layer (the one which contains the objects that will animate along the guide-line). Guiding layer must be first to the guided layer.
To create a guiding layer right-click on the first layer and select Guide from the context menu. You will see an icon appear left of the name of the layer that tells you that this is now a guiding layer. Now you can draw your path using Pencil tool or Line tool only. The line you draw will serve as a motion path for your object in guided layer.
To create guided layer just add one more layer to animation. You can rename the layers for more convenience. This layer will contain the object you want to move along the set path in the guiding layer. Then draw or import your object on stage on this layer. All of this could look something like in the picture below. You can now proceed to animating your object along the guide-line.
Animating the object
On guided layer move your object’s center to the first point of drawn guide-line. Then, having determined the length of your animation, add keyframe on both layers (it is very important to remember that guiding layer has to have the same or more frames than guided layer). In guided layer, on last keyframe, move the center of your object to the last point of drawn guide line and make tween animation between those two keyframes. Giotto will now animate the movement of your object along the path line for the designated animation duration.
Removing the guide
You can remove the guide by right-clicking on the guiding layer and unchecking the Guide option in the context menu, or by deleting the whole layer. Removing the mask will automatically remove Masked option for masked layers underneath it.