Using Meta Objects

Meta objects are cool little 3D surfaces that have been part of computer graphics for a long time. Sometimes meta objects are referred to as blobbies. The principle behind meta objects is pretty simple: Imagine that you have two droplets of water, and you begin moving these two droplets closer and closer to each other. Eventually, the two droplets are going to merge and become a single, larger droplet. That process is basically how meta objects work, except you have complete control over when the droplets merge, how much they merge, and you can reseparate them again if you'd like.

You can also do something that's more difficult in the real world: You can subtract one droplet from the other, rather than add them together into a merged object. They're a ton of fun to play with, and there are some pretty neat applications for them. Figure 6-14 shows two metaballs being merged.

Figure 6-14: Merging two metaballs.

Meta-wha?

Meta objects are a bit like curves and NURBS in that their entire existence is defined by math. However, unlike NURBS or even meshes, you can't control the surface of a meta object directly with control points or vertices. Instead, the shape of their surface is defined by a combination of the object's underlying structure — a point, a line, a plane, a sphere, or a cube — and its proximity to other meta objects.

There are five meta object primitives:

• Ball: The surface in this primitive is based on the points that are all the same distance from a single origin. You can move and scale a metaball uniformly, but you can't scale it in just one direction.
• Capsule: Whereas the basis for a metaball is a single point, the basis for a meta capsule is the line between two points. You can scale the surface uniformly, like a metaball, but you can also scale it in its local X-axis.
• Plane: The meta plane's underlying structure is, as you may have guessed, a plane. You have both the local X- and the local Y-axis for scaling, as well as scaling uniformly.
• Cube: The meta cube is based on a three-dimensional structure — specifically, a cube. You have the ability to scale this primitive independently in the X, Y, or Z directions.
• Ellipsoid: At first glance, you might mistake this meta object for a metaball. However, instead of being based on a single point, this object is based on a sphere. So if you keep the local X, Y, and Z dimensions equal, a meta ellipsoid behaves just like a metaball. However, like the meta cube, you can also scale in any of the three individual axes.

A cool thing about meta objects is that while you're in Edit mode, you can change from one primitive to another on the fly. To do so, use the Active Element panel in the meta object's Object Data Properties. Figure 6-15 shows each of the primitives along with the default settings for them in the Active Element panel.

The Active Element panel always displays the Stiffness value for the selected meta object. This value controls the influence that the selected meta object has on other meta objects. The Stiffness value is indicated visually in the 3D View with a green ring around the meta object's origin. You can adjust the Stiffness value here in the panel, or if you select the green ring (right-click), you can Scale (S) to adjust the Stiffness visually. By right-clicking the reddish, pinkish ring outside of that green ring, you can select the actual individual meta object.

Figure 6-15: The five meta object primitives.

And depending on the type of meta object primitive you're using, other values of X, Y, and Z may appear in the Active Element panel while you're in Edit mode. You can adjust these values here or in 3D View by using the SX, SY, and SZ hotkey sequences. At the bottom of the panel are buttons to either hide the selected meta object or give it a negative influence, subtracting it from the positive, and therefore visible, meta objects.

When you tab back out to Object mode, you can move your combined meta object (a meta-meta object?) as a single unit. Note, however, that even though you've grouped these meta objects into a single Blender object, they don't live in a vacuum. If you have two complex Blender objects made up of metas, bringing the two of them together actually causes them to merge. Just keep that as something you may want to bear in mind and take advantage of in the future.

As a single Blender object, though, you can control a few more things using the Metaball panel, as shown in Figure 6-16. This panel is always available to meta objects, whether in Object mode or Edit mode, and it sits at the top of the Object Data Properties.

Figure 6-16: The Metaball panel.

The first two values in the Metaball panel are resolution values:

• View: Controls how dense the generated mesh is for the meta object in the 3D View. Lower values are a finer mesh, whereas higher values result in much more of an approximation.
• Render: Does the same thing as the View value, except it has an effect only at render time. The reason is that meta objects can get really complex quickly, and because they're generated entirely by math, these complex combinations of meta objects tend to use a lot of computer-processing power.

The Threshold value is an overall control for how much influence the metas in a single Blender object have over each other. This value has a range from 0 to 5, but in order for a meta object to be visible, its individual Stiffness value must be greater than the Threshold value.

Below Threshold are four buttons that control how the meta objects get updated and displayed in the 3D View:

• Always: The slowest and most accurate, this setting is the default. Every change you make in the 3D View happens instantly (or as fast as your computer can handle it).
• Half: This option reduces the resolution of the meta object as you move or edit it, increasing the responsiveness of the 3D View. When you finish transforming the meta object, it displays in full resolution again.
• Fast: As the name implies, this setting is nearly the fastest. When you enable this button, Blender hides the meta objects when you perform a transform and then re-evaluates the surface when you finish. Fast works very nicely, but the downside is that you don't get the nice visual feedback that Always and Half give you.
• Never: This method is certainly the fastest update. Basically, if you try to edit a meta object, it hides everything and never updates in the 3D View. Although Never may not seem useful at first, if you decide to bind your meta object to a particle system as a way of faking fluids, turning this setting on definitely increases performance in the 3D View.

What meta objects are useful for

So what in the world can you actually use meta objects to make? I actually have two answers to this question: all sorts of things, and not much. The reason for this seemingly paradoxical answer is that you can use meta objects to do quick, rough prototype models, and you can also use them with a particle system to generate simple fluid simulations. However, with the advent of advanced modeling tools like multires sculpting and subdivision surfaces, meta objects don't get used as often for prototyping. And with more advanced fluid simulation and rendering technology, meta objects are also used less for those applications as well. They have a tendency to use a lot of computer-processing power and don't often give good topology by themselves.

That said, even though meta objects are used less for these purposes, that doesn't mean that they're never used. In fact, not too long ago, I used a set of metaballs with a glowing halo material to animate the life force being forcefully pulled out of a guy. I could probably have used a particle system or fluid simulator to do this effect, but using metaballs was actually faster to set up, and I had more direct control over where everything was placed on the screen. So don't count meta objects out just yet. These little suckers still have some life left. Besides, they're still fun to play with!