Maya Rendering Guides

Creating a Run Cycle

Running differs from walking in that when the body is at its highest position both feet are actually off the ground. A runner is constantly leaping or bouncing forward. Except for this one difference, a slow jog is almost exactly the same as a very bouncy walk. Also, as the run becomes faster, the body will lean forward more. Since we haven^t done a forward-moving walk cycle, quickly going through the run cycle will also help to illustrate that type of forward motion.

Start out with the front foot just touching the ground, as frame 1 of the next image shows. The child here is in full pose, but if you are going through this yourself, remember the rule about working on one or two control nodes at a time; you should concentrate on the feet and the hips first and then move on to the rest of the upper body. The foot translation and rotation as well as the hip rotation generally have to be worked out together because the hip rotates more in a run, and it^s hard to accurately extend the leg when the hip hasn^t been properly rotated first. The arms are kept more bent, and the body generally rotates and leans forward more. At frame 1, the body is coming down for recoil (squash and stretch), but it^s more efficient if we move on to frame 7 for the opposite pose first and then come back to deal with the recoil. Go to frame 7, select the hand cubes and the root joint, and then move them forward. The left leg should translate forward by a significant amount ahead of the left foot cube, as in frame 7 of the next image.

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• a title="Transform Hierarchy and ParentChild Relationships Mel Scripting for Maya" href="/mel-scripting/transform-hierarchy-and-parentchild-relationships.html">Translate and rotate the foot cubes and the root joint until you have the same pose as in frame 1, except with the opposite leg, as shown in frame 7 below (and in the Color Gallery on the CD). You donnt need to punch in exactly the same values for the cubes in frame 7 as for their counterparts in frame 1 because later on you will edit the function curves anyway, but also because you should get into the habit of trusting your eyes as well. You then need to select the root joint and open the Graph Editor. Select the Translate Z curve, and apply Cycle With Offset. We now have a fixed rate of distance being covered by the run. Go to frame 13 and the body should automatically move forward. Make the child get into the original pose he was in at frame 1 and keyframe the pose. Select the root joint again, and in the Graph Editor, select and cycle all the curves except the Translate Z curve (which is cycling with offset). If you see that some of the curves are not cycling properly, move the keyframes to make them cycle smoothly. You should see curves like the ones below. Repeat this cycling procedure for the other control nodes as well.
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Go back to frame 3, where the body is at the lowest position and is being squashed. For a regular run, the front foot will be flat, as seen in Frame 3 of the next picture; for a sprint, the weight of the body should be on the ball of the foot. Frame 5 shows the stretch; the body is lunging forward and is at its highest point, with back arched, the back leg stretched, and the front knee raised and bent. You also should raise the shoulders a bit at this point.

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Repeat the squash and stretch for frames 9 and 11. When you are done with the footsteps and the arms, cycle all the joints except the Z translation. The Translate Z function curves are cycled with offset. Afterwards, select the LfootCube and the root joint, and look at their Translate Z function curves. If you see them branching out like those in the top two lines in the next picture, it means the Lfoot Cube translate node should be modified. The correct cycle should keep the Z translation values between them roughly parallel, like those in the lower two lines in the picture. Do the same for the hand cubes as well.

Looking at Arcs and Staging

Arcing is another important classical animation principle; in order to imitate life, you need to show motion as arcs, or waves. Nothing in this world moves in a totally straight line. Nature is comprised of arcs and waves, including all motion that occurs within it, as Tai Chi practitioners like to point out. We are told that even something as apparently straight as a ray of light is not perfectly straight. A run cycle, such as the one we just covered, is all wave motions, as you can readily see in the Graph Editor.

But it^s one thing to create wavy function curves and quite another to show them as wavy motions. Consider the often-used example of head-turning. Although the motion itself is an arc, depending on the angle from which you are looking at the head, the head-turning can appear as a straight-line motion. In order to show it as an arc movement, you need to either change the view or dip the head as it turns and then bring it back up. When you have roughly animated your character, get into the habit of going to the camera view and checking the lines the characters motions are creating. If you see a lot of straight lines even though the motions themselves are arcs, perhaps the camera view needs to be changed.

This brings up yet another important animation principle called staging. No matter how great the action in a scene is, it has to be seen clearly in the first place. Staging a character involves making sure the characters actions are being accurately transmitted to the viewers. The run steps above, for instance, were shown in the side view because it best staged the motions of the body. If the same steps were captured in the front view, you would have a much harder time grasping what is going on. Classical animators will often only look at the silhouette of a character to determine whether the characters actions are being staged properly.

Staging also involves making sure that only one principal action is being presented at one time. If you want to show a character getting up from a chair and also flashing a smile, it would be poor staging to have her do both at the same time; it would be much better to have her stand up first and then flash a smile, or vice versa.