Wednesday, 20 February 2013

Rigging Issues

Instead of recording the entire process of rigging, I felt it would make more sense to reflect on some of the problems I faced trying to rig my bizzare insect creature.

Placing the joints and building the skeleton to fit my geometry was straight forward after following tutorial videos placed on our virtual learning environment from a previous module. The key issue I faced throughout the process was some of the strange angles I had included in my turnaround reference image. This wasn't too much of an issue for the spine controls, but for the forearms it caused some problems. Because the arms weren't stretched out horizontally with my model, I couldn't lock off the orient constraint to just the X axis. At first this only meant I had to tweak the wrist on all axes being careful that the translation made sense with the position of the shoulder joint. Where this effected my model however was with the forearm roll function. I planned on using a different multiply function for each arm, using all three inputs/outputs for each axis. However, translating each axis the forearm roll joint by 50% of the wrist joint caused the rig to break:

I decided to leave the forearm roll joint as again my model will be performing a simple stationary animation in the distance when it comes to final shot. However, next time I create a turnaround I will depict horizontal outstretched arms. Perhaps I could have bound the geometry to the skeleton prior to adding the forearm and hand controls, and outstretched the shoulders manually in Maya. After doing so I could then have added the controllers and only oriented along the x axis. This is something to consider in the future when modelling and rigging in Maya.

Weight Painting was relatively successful. I began by taking away the influence on the geometry from all the end joints apart from the toes which require influence when creating the reverse foot lock controls. I find that often the head and shoulder joints require a significant amount of attention. The head usually has influence from neck and shoulder joints which causes parts of the head geometry to warp and drag as the controls are moved. With the helmet, I simply needed full influence on the head geometry from the head joint. I also usually find that the shoulders need pinching under the arms as to not drag the chest and rib areas when the controls are rotated. I usually find that removing influence from around the arm pits adds some level of realism. One problem I experienced around the upper body was with the nose of the helmet as shown below:

I immediately assumed that some small level of influence from a joint lower down the chain was causing the vertex to drag down. However, after going through every single joint with the colour gradient mode set I simply couldn't locate the culprit (From the screenshot I am aware that working in high quality preview mode is bad practice when not focusing on texturing or lighting. When working at home I always work with the textures deactivated to make Maya run as smoothly as possible. However I grabbed this shot whilst experimenting with my UV textures on the fast running college computers).

The most frustrating issue I faced was weight painting the feet. Because of the stubby length and height of the feet, the joints felt squashed up and most of the time caused the feet to shrink when tweaking the custom attributes. It was hard to remove influence from the ball joint of each foot for the toe tap and peel heel controls. It meant that the peel heel came out looking like a limited 'stand tip' control without the ball joint firmly planted on the ground:

As you can see the joints become squashed together even causing the geometry to appear as if it's shrinking. The toe tap was equally unsuccessful:

Again the alien isn't so much tapping its toe as rocking back completely on its heel. Fortunately, with the creature remaining stationary in my final shot, I will not need to worry so much about the peel heel or toe tap controls. If the custom attributes had been successful I could possibly have applied them very subtly to add extra detail and realism to the animation. Fortunately, I managed to apply the fist controls, animating each finger separately. Hopefully I will be able to get some expression in the hands with my animation.

The final point I want to raise wasn't an enormous issue, but would have been if I had wanted my alien to walk. I would have had to better consider the use of inverse kinematics or 'IK handles'. For the legs I added one IK handle each running top of the leg down to the ankle joint. I wasn't aware that adding multiple IK handles was a possibility until a classmate pointed it out to me later. At this stage I was already satisfied to some degree with the rig and didn't want to loose time correcting something that will have little to no effect on the final scene. The single IK handle in the triple jointed leg rig means that the geometry founds in on itself when the root control is lowered:

After completing the rig, I locked all of the controls with the limit information in the attributes editor. This means the rig cannot be broken. I then grouped everything together for housekeeping. Bellow is a quick posed model of my alien:

Although I am working outside of my desired area of specialisation, I feel that I am constantly improving my understanding of the workflow involved in the full game development process. For example, through my rigging practice I am now aware of the problems angled geometry can cause when adding adding constraints.

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