3D Animation Workshop: Lesson 8: Mind Candy | 2 | WebReference

3D Animation Workshop: Lesson 8: Mind Candy | 2

Lesson 8 - Mind Candy - Part 2

Changes in the surface geometry of objects are approached in two general directions. At one extreme is the editing of individual points or small, localized, surface areas. For example, the points defining the shape of a character's mouth can be edited to animate the mouth and give the impression of talking. The rest of the face remains unchanged. This is what we may call local editing. Local editing of object geometry is a feature of high-end applications rather then low-end ones.

At the other extreme, the whole object, or a large section of it composed of many points and polygons, is manipulated. Such large-scale changes in object geometry are generally called "deformations." The high-end applications have an extremely powerful range of deformation tools, but even the low-end applications will typically have a fairly good range. Users of the low-end tools must develop a strong command of the available deformation tools to create effective animations.

Let's explore deformation by starting with two primitives, a cube and a sphere.

Note that the objects have been given a checkered surface. This will help us to see the effects of deformation better.

The first thing we can do is to simply scale the objects disproportionately. In the next example, the scale is doubled in y (in height) and halved in the x dimension. The z (depth dimension is unchanged.

Note that a second light has been added, brightening the scene. Note also how the shadow cast on the cube by the elongated sphere creates a sense that there is a single scene, not just two disembodied objects.

Disproportionate scaling of objects is not properly considered "deformation" in 3-D graphics, as we'll soon see. But disproportionate scaling of curved objects (like the sphere) does create an effect that we might use for a simple kind of change in object geometry.

Contrast the above with a true stretch of the objects.

This is a true deformation. The change of object geometry is more evident with cube, but look at the new sphere as well. The shape is distinctly different than the simple elongation above.

Now we squash the objects down

Squash and stretch will reveal their powers to us very shortly, as we look at them in animation. In traditional drawn character animation, human bodies are often given an elastic effect to suggest energy and motive. A character squashes down a bit in anticipation of taking a step, stretches out as the step is taken, a squashes down again as foot meets ground. This caricaturing of motion is just as important as caricaturing of shape in creating effective animation.

Another simple and important type of object deformation is bending.

The effect is much clearer and more striking in the cube, and we can already begin to imagine how bending the cube back and forth in an animated sequence could be quite effective. Look carefully at the sphere, though. The checked surface reveals that it has been bent.

Contrast the bend with a twist.

The only indication of deformation on the sphere is revealed by the surface pattern. The geometry appears unchanged. By contrast, the cube has been obviously deformed, and the effect of the twist would be evident even without a pattern on the surface.

Now let's use these simple tools to make an animation.

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Created: Apr. 22, 1997
Revised: Apr.22, 1997

URL: http://webreference.com/3d/lesson8/part2.html