Setup

The QStretch->Setup command in the Actor module lets you apply one or more types of motion and deformation modes to the selected model. The faster the motion of the model, the more pronounced the deformation effects.

After you set up the Quick Stretch parameters, you can view the effects by dragging the object, and you can also keyframe the object's movement and play it back as an animation.

The overall Quick Stretch effect depends on the configuration of motion and deformation that you choose.

For a general description of this feature, refer to Quick Stretch, and see the Quick Stretch Tricks section of the Animating User's Guide.

Procedure

1. Select an object in node or branch selection mode.
   
   Make sure the objects have enough definition to give a good result. For example, a default cube should be subdivided quite a bit to show the effect of the deformations.
   
   
2. Choose the QStretch->Setup command.
   
   The Quick Stretch Setup dialogue box is displayed.
   
   
3. Select the desired component using the Current Component menu.
   
   For each selected motion component, select or deselect the desired deformation Mode (Flex, Stretch, and Yield).
   
   
4. Set any options such as Deformation, Lock Deform, Maximum, or Sensitivity.
5. The Key button creates a keyframe only for the active parameters of the current component. The Key All button creates a keyframe for the active parameters of all the components.
6. Click Ok or Cancel.

Parameters

Override Parent's Setup

Specifies whether to deform an object relative to its parent's settings.

If this option is selected, the object deforms as if it were a node without any parent, regardless of whether the parent has Quick Stretch applied to it or not.

If this option is not selected, the parent's setup is used instead and the deformation is performed considering all the object's points relative to the parent's centre. The effect continues up the hierarchy until the first object with its own setup is encountered.

Tagged Points Only

If this option is selected, the deformation is applied exclusively on tagged points.

Current Component

This menu allows you to choose each motion component and then set its deformation parameters as required.

When you select a component, the deformation values you set are related to that component of the object's motion.

• Velocity allows you to set deformation values related to the linear velocity of the object. For example, a car moving at a steady speed of 100 km/h has a linear velocity of 100.
• Acceleration allows you to set deformation values related to the linear acceleration of the object. Acceleration is specifically related to a change in velocity. For example, a car moving at a steady speed of 100 km/h has a velocity of 100, but an acceleration of 0.

The Acceleration component may include discontinuities or sudden large values when the velocity comes to a stop. To remove these discontinuities, you may have to plot the motion vectors and edit the acceleration curves. For more information, see the Plotting Trajectories section of the Animating User's Guide.

• Rotational Velocity allows you to set deformation values related to the rotational velocity of the object (for example, of a ball that is spinning).
• Rotational Acceleration allows you to set deformation values related to the rotational acceleration of the object.

Mode

These options let you activate or deactivate each particular deformation effect. Each effect is designed to be tweaked separately, but the effects are compounded if more than one is selected.

Tip:

Try tweaking each effect separately as much as possible so that if you use them all together, the resulting deformation is easier to predict.

Flex

The object appears to bend or flex in the direction of the motion, mimicking the effects of air or water resistance.

• Curved Profile: As the object is displaced, its profile curves as in the illustration. This makes it suitable for objects of a flimsy composition, such as a piece of paper which is bent by the wind from its own displacement.
• Linear Profile: As the object is displaced, its profile will be a straight edge. This is suitable for objects composed of a solid material, such as a truck trailer, which you would not expect to curve when the truck moves, but still might shear a little bit.

Stretch

The object elongates in the direction of the motion and becomes thinner in the other directions, such as in the classic cartoon "squash and stretch" effect.

• Keep Volume: As the object stretches to become longer and thinner, Quick Stretch preserves the object's approximate overall volume.
• Free Volume: Quick Stretch does not preserve the volume. This has an effect if the object is moving in many directions at once.

Yield

Depending on what mass is assigned, a moving object appears to bulge due to the internal displacement of its mass.

• Linear Profile: As the object is displaced, its profile will be a straight edge.
• Curved Profile: As the object is displaced, its profile will curve.

Lock Deform

By default, deformations are applied to all axes of the model. Lock Deform allows you to "lock" or prevent the deformation from being applied on the selected axes.

While this may give odd results, it can be useful in representing the object's deformation. For example, a sheet of paper should easily deform along the axis pointing out of the plane of the sheet (for example, in the case of a default grid, this is the y-axis).

Conversely, you would not expect the sides of the sheet to deform as you slide it in the other directions. To avoid this, lock deformation on the x and z-axes of the paper. Some experimentation may be required to attain the desired effects, depending on the mass assigned to your object.

Maximum

Each deformation is directly related to a motion component. The faster the object is moving, the more it is deformed. At some point, however, an object should normally reach a maximum deformation depending on the mass assigned to it.

For each mode (Flex, Stretch, Yield), the maximum values are defined according to the bounding box of the object at rest. For example, if the maximum for Stretch is set to 1.0, the object elongates to a maximum of one time the size of its bounding box (a total of twice the size). With the maximum at 0.5, the object would elongate to 1.5 times its initial size.

No damping is applied, so the maximum might require a bit of tweaking to avoid the object coming to an abrupt stop.

Sensitivity

This is the scaling factor applied each of the effects. These values express the sensitivity of the deformation relative to the object's motion.

Modes: Overview

This box graphically represents all the activation switches for each motion component in the main part of the dialogue box. At a glance, you can see which deformations are currently activated for all four motion components. Activate or deactivate a component and mode by either deselecting the Modes overview box or in the appropriate option in the dialogue box.

Key

Maximum values and sensitivity levels can be animated. The Key button creates a keyframe only for the active parameters of the current motion component, as shown in the dialogue box. You can move the time line pointer to other frames without exiting the Quick Stretch Setup dialogue box to create more keyframes in this manner.

Key All

Creates a keyframe for the active parameters of all the motion components.

Cancel

Cancels the new parameters without removing the animation already keyframed.

Ok

Accepts the new values and/or creates Quick Stretch information for the selected objects.

Last updated 02-apr-1998