Angela Spearman wants her Cinema 4D characters to move convincingly; Glen Southern’s standing by with assistance
Download the support files for this Cinema 4D Q&A here.
Having a fantastic rigging system is one thing, but having the right geometry to rig in the first place is another. A lot of models start out as high-resolution sculpts that then need retopologising, but all the rules still apply when it comes to rigging time. Good topology and geometry are essential for creating a character that moves and deforms in a predictable way. Cinema 4D R13 comes with several ready-made rigs that you can add to your characters. Once the rig is added and correctly positioned, it’s then bound to the mesh. This is where the good topology comes into play: if you have good edge loops around key areas, and the polygons are created and laid out correctly, there will be only a limited amount of weight painting to do, and all the joints will deform as you expect when you start to animate. So when you model a character, there are certain rules and tips that will leave you with a model that’s easy to rig.
First, make sure there are good edge loops around all the character’s key joints. Any area of the mesh that will bend will need to have a higher density of polygons (and therefore vertices) than areas that won’t be deforming.
For example, the wrist, elbow and shoulder joints are crucial areas to focus on to get realistic arms. The arm may be animated up, down, backwards and forwards, and often twisted into odd angles.
The elbow may have to angle at almost 180 degrees, and the wrist may need the same, especially in cartoon characters. You can lower the polygon count in the arm as long as the shoulder and elbow and wrist areas have these extra edge loops.
Once you’ve modelled your character, it’s always wise to go back over it and check each joint area to make sure there’s enough geometry for the required animation. If you know the head will never be required to turn in extreme poses, then you don’t need to worry too much about extra geometry in the upper chest, neck and chin areas.
If, however, the character will be expected to turn its head 180 degrees and look backwards for some reason (for instance, it could be running while looking backwards in an exaggerated pose) then it’s better to be safe than sorry and build in the correct amount of loops and polygons to allow the pose to happen. It’s better to give the model enough geometry to allow extreme poses, rather than find out at a later stage that it isn’t working well enough.
Wherever possible, try to line up the vertices in regular loops or in vertical or horizontal lines – anything that makes the rigging and weighting easier and more accurate. If vertices are all over the place and hidden behind each other, weighting can become very tricky, so get into the habit of laying down predictable grids of polygons that aren’t too stretched out or compressed. This will all help at the rigging stage.
Cinema 4D has a really powerful Pose Morph tag that enables you to animate anything between two pre-set poses, such as two facial expressions. To ensure that these facial expressions work correctly, areas such as the eyes, nostrils and mouth all need a continuous ring of polygons (edge loops) to give good deformation. Good topology quite often resembles the look of skin folds and creases.
Make sure that there are enough edge loops around the eye for it to be fully opened (and opened wide for exaggerated poses) and squeezed tightly shut. Exactly the same applies to the nostrils and mouth area on most characters – but not for our alien.
For this project I modelled a fairly low-res alien character, and then, just before the rigging took place, I went back over the model and added some extra loops and cuts to help with the rigging. The results can be seen in the second accompanying video, once an advanced biped rig is added and bound to the mesh.
Three top tips for rigging characters
Use the Knife tool to add loops
One of the best tools for adding accurate loops is the Knife tool. Set it to Loop and it will cut you an accurate loop right round the required polygons.
If in doubt, add a loop
If you aren’t constrained by poly counts and you think an area may need to deform, add extra loops to be sure.
Adjust weighting after posing
After rigging you may not be able to see problems until you animate, but you can still adjust weighting when the character is being posed. Sometimes it helps.
Glen Southern is a 3D artist with over 15 years of experience in film, TV and games. He’s also the owner of SouthernGFX