A Smart Bone Dial (SBD) can be used to control Switch layers...it's a great technique and I use it all the time, but there are limitations to be aware of.
The main limitation is that, unless you use step keys to animate the the Dial, the switch layers will always play linearly. This is important if you're using the Switch for mouth shapes and you need to jump around to different drawings non-linearly. Also, if you use this method for Switch layers, be aware that you cannot use it for Interpolate Sub-layers because: 1.) when you use Step keys, you do not get interpolation, and 2.) if you don't use Step keys, you will get interpolation but the layers will play in sequence.
So, if your intention is to use this for mouth shapes, it can be used for that but I recommend using the Switch Selection window instead because It's easier to setup and use, and can be more effective.
That said, this technique has a lot of other great uses.
Here's a walkthru for setting up an SBD for a Switch layer...
1. Make sure you have Copy Previous Key set as your Default Interpolation.
2. Create a Bone layer and then create a Switch layer under the Bone layer.
3. Fill the Switch layer with the content you want to switch between (at least two layers.)
4. In the Bone layer, create a bone and give it a name (like 'eyes' or 'mouth' for example). For the purpose of this walkthru, let's call it 'switch'.
5. With the Select Bone tool active and the 'switch' bone selected, click on Bone Constraints. In Angle Constraints, replace 90 with 0. The values you use can vary depending on how you wish to use the dial. For now, I want the dial to be able to rotate 90 degrees to the right.
6. Reduce the bone strength to 0 so it doesn't affect the artwork.
7. Open the Actions window.
8. With the bone selected, click New Action in the Actions window. An action will appear with the bone's name, 'switch' in this case. Notice the timeline has changed. We are now looking at the Action's timeline.
9. Advance to frame 1 and click on the bone. Two Smooth keyframes will appear, one at frame 0 and the other at frame 1. R-click over the second keyframe in the Selected Bone Angle row (the red one) and choose Linear.
In a Smart Bone Actions, it's good practice to set a keyframe at frame 1 because this key defines the interpolation mode you will be using in the Action (usually you want this to be Linear) and keeps it separate from the default interpolation mode you want to use during animation. (Usually this will be Smooth, but the point is, by defining frame 1 as Linear in the Action, you're free to use whichever Interpolation mode you want for frame 0 without affecting the Linear mode used in the Action.)
10. Advance to the frame where you want to end your Action. You want to use enough frame to cover all drawings in your switch, so if you have 10 drawings, go to frame 10.
11. Turn the dial all the way to the right. Because of the bone constraint we set earlier, it should stop at -90 degrees.
12. Click the bone again to create another keyframe. Because we have Copy Previous Key set in Default Interpolation, another Linear key is created. Yay, we now have a Smart Bone ready.
Note: alternatively, you can select the bone before step 5 and choose Bone >Make Smart Bone Dial, and enter the parameters you want in the panel that opens. If you do this, you can skip steps 5 - 12.
So why did I bother going through all these steps, you may ask? Using the Make SBD command may be appealing to beginners for its convenience, but because it adds things I don't need or I will have to change, I prefer to create the SBD myself and get
exactly what I need. Also, even if you want to use the command, it's good to understand exactly how the parts of an SBD works so you know how to adjust and fix things when they go wrong.
13. Now we should make a decision about the keyframe at frame 0. Since this will be the default Interpolation mode during animation, you want to set it to the mode you intend to use. For Switch layers, this will probably be Step mode when you want to be able to animate the order of the layers non-sequentially. This is the most typical choice for anything with multiple drawings of the same item, like mouth shapes, eyes, hands, etc.
Anyway...
13. Select the Switch layer and open the Switch Selection window. You should see the currently active layer in the switch in the window.
14. On frame 1, select the first drawing. If the drawing is already visible, move the slider and move it back. The point is, you need to create a keyframe for the drawing at frame 1.
15. Advance to the next frame, and advance the Switch Selection slider to the next drawing. Another keyframe is inserted. Continue for all 10 Switch layer layers.
16. In the Actions window, double-click on Mainline. You will exit the Actions editor and return to the Mainline where you can animate the Switch using the SBD.
If all the steps were followed correctly, you should now be ready use your Switch layer SBD. If it's not working correctly, double-click on the Smart Bone Action name to edit it.
There's a lot more you can learn about Smart Bone Actions/Dials and Switch Layers but the above info should cover the basics. If this seems like a lot to remember, it's not really...after some practice, you should be able to run through everything you need very quickly without thinking much about it.
Hope this is enough to get you started.
