I don't remember the first person to come up with the idea of using stroke shapes for arms and legs but I am really starting to like it! Whoever you are THANK YOU! It really is a freaking awesome trick. With features like smart bones, stroke exposure and follow path you can do some amazing stuff.
For this character I originally created everything the way I always do with filled shapes for arms. As we all know you need to do a lot of tricky stuff to get the joints to bend nicely, smart bones, extra bones etc. Then I tried to animate a simple thing like rolling up his sleeves. Freaking nightmare with filled shapes. Getting everything to line up.
I kept looking at the style I was using and thought, this would be a great time to use stroke shapes for arms. The character is very simple, with a simple shading effect. Arm bending would be a breeze with smart bones. The arm only has 3 points. Just two end points and one point at the elbow.
For the rolling up the sleeve efffect, the trick was to combine 3 features of Anime Studio:
Smart Bones
Stroke Exposure
Follow Path
Arm and Sleeves
Stroke exposure works based on the initial direction the vector is drawn. To do the sleeve rolling up the way I wanted I had to "reverse" the direction of the vectors drawn, so that the arm stroke exposure is based at the shoulder, and the sleeve is based at the wrist. When the sleeve goes up, the arm shape stroke exposure increases, the sleeve stroke exposure decreases.
The next tricky part is the sleeve cuff. How to pull that off?
(I printed out the Anime Studio documentation and placed it under my pillow while I slept. The next morning I had a brainstorm!
)I drew the cuff of the sleeve on a separate layer. I assigned a "follow path" to the arm stroke and set the layer properties to rotate to follow path. I adjusted the initial follow path setting so it lined up with the exposed arm shape. The arm shape has round end caps and it stops just inside the black inner shape of the sleeve cuff, making it look like the arm is "inside" the sleeve.
Next was the smart bones. I created a single smart bone for each arm with two actions.
The sleeve starting or default position is a little bit more than half way down. Just past the elbow.
The first action pulls the sleeve down to the wrist, the second goes up to the shoulder.
In each action I adjusted the stroke exposure for the arm and sleeves so they match up. This lined up perfectly because both strokes were identical in length and always stayed lined up.
Next I adjusted the follow path setting for the sleeve cuff so it followed the arm path as the sleeve moves up and down the arm.
The next step was to modify the sleeve cuff during the smart action so that it appears to change in bulk as the sleeve moves up and down the arm. The illusion is perfect.
I then created a smart bone action for the forearm bone and decreased the curvature of the arm at the elbow point.
The only extra tricky effort was masking the TOP part of the sleeve stroke where it joins the shoulder. I didn't want a simple flat end, or a perfectly round end cap. I needed the top of the sleeve shape to appear as part of the rest of the jacket. BUT... I also needed the arm shape to be able to change layer order, go behind or in front of the body.
I put each arm group of layers (hand, arm, sleeve) into its own group inside the bone layer. I set the group masking to "reveal all". I then created a very simple mask shape to hide the top of the sleeve stroke so that it "matched" and lined up with the jacket shoulder area. I tweaked some smart bone actions for the bicep so everything looks correct during rotation.
Each arm group layer can now have animated layer ordering as needed and will line up with the shoulder of the body.
The best part of this whole thing is that the sleeves can be rolled up and down regardless of the bending of the arm. The cuff of the sleeve just follows along the curve of the arm. It all just works silently behind the scenes.
