Arcs. Animators are obsessed with arcs. This is because most organic actions happen along an arched path, giving fluidity and realism to human and animal motions.
Mechanical movements, on the other hand, usually happen along straight paths.
Whether you are animating an organic being or a mechanical device, Blender allows the tracking of motion paths. This is extremely helpful when animating, and can give you answers when you watch the movements you create and feel that "something isn't quite right".
- Open the file
005-Tracking.blend. It has our character Otto with some very basic and unfinished animation of a jump. Let's track the arcs so we can make our animation better. - First, let's track the path made by the
Hipsbone, since it's the center of gravity for our character. Select it, make sure you're on side view (Numpad 3), go to the Properties window, on the Object Data tab, and find the Motion Paths panel. Make sure the options Frame Numbers, Keyframes, and Keyframe Numbers are selected and click on Calculate Paths. You'll see a result similar to the next screenshot:
Blender has tracked the path of the Hips bone in the 3D View with highlights on the frames, marking the keyframes with squares and the interpolated frames with dots. The frame numbers also have a different hue where the keyframes are set. It's very helpful to really see the path and keyframes in 3D, so we can spot any imperfections in the motion. Let's enhance it.
If you scroll the timeline, the path remains in place and the current frame is highlighted. First, let's try to adjust our current keyframes.
- In frame 1, move the
Hipsbone a bit below its current position and replace its LocRot keyframe (I). At frame 4, drag it up a little and replace its keyframe. - You'll notice that the path hasn't changed despite your updates. You need to click on Calculate Paths again to see the updated arc of motion. The change may be subtle, but isn't that what animation is about?
- Let's continue tweaking the keyframes. On a Graph Editor window, make the Y Location the only channel visible for the
Hipsbone. This channel controls the up or down movement. Edit its handles until you get a softer curve. You can change the way the handles behave by selecting the desired mode in the V menu. The next screenshot shows it before and after the editing:
- If you click on the Calculate Paths button again, you'll see that the motion curve for the
Hipsbone has improved significantly. The following screenshot shows the new and improved path:
- When you're happy with the
Hipspath, click on the Clear Paths button on the Motion Paths panel. It's time to check the paths for other interesting bones. After the hips controller, you can check the head, arms, and feet, since they are commonly the center of attention in this kind of broad movement.
Just be sure to remember the bone hierarchy when correcting paths: when you change the position of a parent bone, such as the Hips, the paths of its children (FK arms, head, and so on) will also change. That's why we should begin with top level bones on the rig hierarchy. The file 006-Tracking-complete.blend has this recipe with the Hips path corrected.
Blender has a nice feature for calculating the Motion Paths for bones and other animated objects in the 3D View. These traced paths allow the animator to easily see what problems occur in the motion path and what frames should be corrected. By carefully tweaking the bones which are higher on the rig hierarchy first, the animator can quickly build good animation arcs.
Along with the Motion Paths feature, Blender has a similar feature called Ghost. This feature is also called "Onion Skin" in other animation software, and allows the animator to see a translucent copy of the selected bone or object for different positions on the timeline.
This feature is located on the same Object Data tab as the Motion Paths, and can be configured to display the translucent copies in various ways. One advantage of it over the Motion Paths is that the copies are automatically updated on the 3D View when you change a keyframe. The Ghost feature can be used alone or together with the Motion Paths, giving very good visual aids to the animator.
Chapter 7: Easy to Say, Hard to Do: Mastering the Basics