Vector Layers: Bone Mode

Bone mode is sort of a pre-animation phase. You don't draw shapes in Bone mode, but you don't animate either - you set up controls that will help you animate later on. The purpose of setting up bones is exactly what you might think: creating a rigid skeleton inside your drawing. Later on, during animation, when you want to move an object, bones make the job easy. By moving a single bone in the arm of a character, for example, the whole arm will move with it. Around the elbow, the drawing of the arm will bend and stay smooth (as long as the bones were set up well in the Bone editing mode).

Any type of animation that you can do using bones could also be done by just moving the points of a drawing around over time. However, for certain types of animation, bones make the job a lot easier.

Bone mode for a vector layer is where you assign which points are attached to which bone. To set up the bones themselves, you need to create a Bone layer, and this is discussed in the section on bone layers. The vector layer must be contained within the bone layer in the layer hierarchy - bone layers can only control vector layers that have been assigned to them. The Layer Palette chapter discusses how to place a vector layer inside a bone layer. Also, the Tutorials are a good place to learn how vector layers and bone layers work together.

Bones are not visible objects in Moho - they're just animation tools and they won't show up in a final rendering. Bones are used to manipulate points, and hence curves and fills, which do show up in the final rendering. The way this happens is that points are bound to bones. When a bone moves, any points that are bound to it move as well. Below is a picture of some points and bones. The points have been grouped according to which bone they're bound to. The second picture shows the same object after the bones have been moved. Notice how the points follow the bone they're bound to (and how the curves pass smoothly through the points, wherever they move to).

Bone Tools

The following tools are available in Bone mode.

Select Bone
Using this tool, you can click on a bone to select it. For vector layers, the reason you would want to select a bone is to assign which points should be bound to it. Click anywhere besides a bone to de-select all bones.

Bind Points
The Bind Points tool operates exactly like the Select Points tool described in the Draw mode chapter. Use it to select a group of points to bind to a bone. In order to use this tool, a bone must first be selected. When a bone is selected, the points that are currently bound to it are automatically selected as well. Use this tool to add or remove points from that selected group. When the correct group of points is selected that you want to bind to the bone, press the spacebar - this tells Moho to perform the binding.

Attach Layer to Bone
Use this tool if you want to attach everything in the layer to a single bone. The entire layer will then move however that bone moves. If you want an object to bend and move with two or more bones, then this is probably not the tool to use (use the Bind Points tool instead).

To use this tool, just click on the bone that you want to attach the layer to, or click on empty space to detach the layer from a bone it was previously bound to.

Test Bones
The Test Bones tool is a glimpse of what you'll see in Animation mode. It is used to test whether a skeleton is set up and working properly. Although it moves bones and points around, the changes it makes are only temporary. When you switch back to another tool, the skeleton is reverted back to its original shape.

To test a skeleton, just click and drag the various bones that make it up. If points have been bound to the bones, they will move as well. The way the skeleton and the bound points move with this tool is exactly how they will move in Animation mode. If some part of the skeleton doesn't move correctly, you can find out with this tool and fix it before you start animating.

A Tip: Good Bone Placement

Getting bones to work their best takes a little planning. The combination of how points and curves are arranged in a drawing and where bones are placed can make the difference between believable motion and just goofy bendiness (which sometimes isn't all bad).

We're going to illustrate an example of a common situation that comes up when using bones to animate a character. This example illustrates some bones used to control a leg. A similar setup might work with an arm, or any joint that works like a knee or elbow (one that only bends in only one direction). Below is a picture of the leg we're going to discuss.

The next picture shows which points have been bound to which bones.

The important thing to notice about this leg is the arrangement of the points and bones around the knee. The two points and the joint illustrated below are arranged in a diagonal line that is offset by 45 degrees from the line of the bones.

The diagonal offset of the points and the joint, together with the fact that both of those points are bound to the upper bone, mean that the knee can be bent 90 degrees without folding up on itself. The picture below shows the knee bent. Notice which points moved, and which didn't, depending on which bone they were bound to. (Another little tip: the point on the inside of the knee had its curvature reduced (in Draw mode) so that when the leg bends, the inner curve is not as round as the outer one.)

As mentioned, this leg was set up specifically for a knee-type joint - one that bends in only one direction. What happens if we bend it the other way? The picture belows shows the result. It isn't pretty, but you probably won't want to bend the knee that direction anyhow. Just keep in mind that this little trick of offsetting two points and a joint by 45 degrees from the line of the bone isn't appropriate in all cases.