Flexible Animation System for Fingers and Hands
For many years as a character animator I have wanted a system to aid with the animation of fingers. It’s one of the things that tend to be done as an afterthought when pushed for time on a production, but there is no doubting that some of the nicest animation will always have really great hand gestures. The balance is trying to find the balance between time and ease of animation. If you are really pushed for time, it would be far better that you could store hand poses that you use most of the time, with a view to having a robust toolset to allow you to refine them afterwards.
I recently wrote a system called Digit that goes some way towards addressing this issue in production. The key to this system working well was to provide a UI that was intuitive to the way people currently work in max, and making it minimal and simple enough that it didn’t need too much understanding. This article will hopefully explain the process that I undertook in planning and executing this system.
Planning the control layout
I usually start with some sketches – i have a technical journal that I write ideas and loops into. This over the years (and much to my chagrin) has replaced my sketchbook but it does give me a kind of technical reference for everything. I will scribble UI ideas down before I code anything, as it helps me to plan in advance potential layout conflicts. It is by no means final but it gets me thinking about how everything is going to interact. The thing to remember is that it’s not something you’ll proudly display, but it helps to organise your mind and avoid any UI layout problems along the line. UI design is a hard thing to do, generally people will tell you when it is wrong in a heartbeat and not even notice if it is right. It’s one of those thankless tasks that only you can appreciate.
With Digit I felt I could deviate from the look of the max UI – firstly, square controls were simply not going to cut it, and I wanted to allow control to adjust the layout when running in either a portrait or landscape mode. The FlowLayoutPanel is built for this task and I’ve used it extensively for my controls up to now. The layout logic was pretty simple, I didn’t want to separate the controls too much, what it gave me was two main panels – the selection interface, and the slider controls.
The critical thing for me in terms of the functionality of the system was that it was as intuitive as possible, and mimicked a lot of the same methods as the native max UI. This was mainly the use of CTRL and ALT to add and remove from selection, and the double-click hierarchy selection. My other consideration was to try to keep the dialog as minimal as possible. I had setup finger controls in the past and found, due to the nature of wanting them to be able to control individual fingers, that they can become large slider interfaces. I thought that this time i would be able to use less and still have the same level of control. Here is what I came up with in the end, they are the same UserControl, they have a hand property, Left and Right which decides what UI colour they get.
Selection based curl slider
I did this by having a two stage approach, working on a specific selection or on the entire hand. If no finger element was selected, the curl slider affected the entire hand. If a particular finger had been selected, then the curl would only operate on that finger. The same went for resetting the finger position. This worked well, you could quickly set up different poses based on others.
Splay and Thumb position and rotation were different. You don’t want to splay individual fingers, it looks odd so this acts on the entire finger rig. And individual thumb position and rotation are also necessary. However the thumb curl operates on the global curl slider.
The +Thumb button was something that came from the evolution of the control and testing it on some real characters. Sometimes, you didn’t want to move the thumb but still move the fingers. This checkbutton allows you to affect the thumb curl and splay with the other fingers – as before, it is based on the selection, so you have to have no part selected for this to work.
Its all put in place with a bit of simple matrix rotation. You can prerotate a matrix according to an angle, so each time the slider moves, it is calling a function that supplies the current transform and returns a new transform matrix that is prerotated by the angle from the slider.
Medial,Distal and Proximal Selectors
The three selectors to the left of the fingers are to select across the first, second and third bones. I thought this gives an extra control if the automatic blended rotation of the fingers isn’t quite enough to get the hand pose you are after.
Pose Storage and Mirroring Transforms
I have been using XML for a while now to store any sort of pose when I use a reference transform monitor to store a node. Most of my facial animation systems and rig setups use these. Once the directory is specified, you can store the local transform of each node and that’s all you need. I use an XMLLayoutPanel to handle the files. Its a dotnet user control I released a while ago that handles all the layout and even lets you specify a custom thumbnail. Check my previous blog post if you want to have a go at using it.
When you apply it back on the hand later, you multiply the current finger’s parent transform with the XML preset’s local transform and you have applied your stored preset. Because you extract the local transform, the pose is the same, even when applied to a different hand position as you are making a new transform matrix from the current parent’s position. When you want to mirror the transform to the other hand, that is a little more involved.
You start by reading the local transform of the finger nodes. Then, you Mirror the transform matrices of all bones, by creating a mirrored transform around a common parent (like the character’s root). However the other arm is not necessarily in the same position. So, you need to create a mirrored transform of the hand too. Once you have this, you can get the mirrored bones local transform matrix. This becomes the one you use, as you can then multiply this mirrored local transform onto the current location of the parent (i.e. the opposite hand) With this you can paste a hand pose from one arm to the other, regardless of the arm position. I was grateful for all of the brilliant examples on the CGTalk board to help with this, specifically from Paul Neale.
It is possible to set up a character with this complete hand animation system without any Maxscript. This works on Bipeds, CATrigs, Puppetshop rigs and custom bone rigs, so hopefully it will be useful for many projects to come.
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