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Animating the Rocket

To animate the Rocket you will work both with the objects transformation information and its shape. The basic liftoff will be created using keyframes set to the translation of the surface while a cartoon-like squash-stretch will be applied at the geometry (SOP) level to anticipate the lift-off.


Part One: Setting Keyframes on the Rocket

Setting keyframes allows you to map a parameter against time. Keyframes represent key points in time where you know how your object should be positioned. The keys are linked using animation curves that can be edited in the Channel editor. These curves let you define the motion in-between the keyframes and can be used to significantly alter the quality of an animation.

1. Set Keyframes

You want to animate our rocket to move from an initial location at frame 1 to a new location at the last frame.

In the Network Editor, click on the rocket object. In the Parameter pane, RMB-click on the Translate parameter. From the resulting menu, select Set Keyframe. You’ll see the edit fields turn green to indicate that they are now under keyframe control, and will change over time.

Drag the Playbar all the way to Frame 300. Click in the Translate-Y parameter for the rocket, and type in: 55. The rocket should go off screen and a new keyframe is set.

Play back the animation using the animation controls. You can move between frames and scroll on the time slider using these controls. You will notice that the rocket starts off slow and speeds up as it climbs. This may not be the behaviour you want. You can use the animation curves to alter the speed of the animation between the keyframes.

2. Scope the Channels

RMB-click on the Translate parameter, and select Scope Channels. A window appears with a graph of the rocket’s movement over time. In this case the curve represents the translation along Y (/ty).

3. Change the Interpolation

Move the window out of the way of the Viewport if necessary (alternately, you could have switched one of the panes to be a Channel Editor pane). Select the /ty channel segment. You will notice that its Interpolation Function is set to: cubic(), change this to: easeout() by clicking on the arrow next to the function field.

You should now notice that the rocket starts off fast, and slows down as it reaches its peak.

4. Edit the Start Frame

Click drag a bounding box over the first key at frame 1. Its values are displayed in the fields at the bottom of the editor. Change the T value to 30. This delays the takeoff for 30 frames. This time will be used to animate squash and stretch on the rocket in the next few steps.

Close the Channel Editor window and playback the animation to preview the results. The motion now reflects the new shape of the animation curve.

Part Two: Adding Squash and Stretch to the Rocket

To add a cartoon effect to the rocket, you will animate the parameters of a Twist operator at the Geometry level of the rocket. In Houdini you can animate at the object level or at the Geometry level.

1. Add a Twist SOP

Click on the rocket and press i to enter into this object. Click on the merge1 SOP to highlight it. With the mouse in the Viewer pane, press tab> Twist. Click-drag around the whole rocket and then RMB-click to accept. The twist handles are shown at the centre of the rocket. In the parameter pane, set the following:

Operation to Squash & Stretch;
Primary Axis to Y axis;
Strength to 0.

Click on the vertical pivot handle to and drag the pivot to the base of the rocket. Now all the squashing will take place around this point.

RMB-click on the Strength parameter and select Bind to Viewport Handle Ladder. This will make it possible to use a value grid to set the strength interactively in the viewport.

2. Keyframing the Squash

Make sure that your current time is set to 1 and the twist operator’s strength parameter is set to 0.
Click with your \ on the Strength parameter and select Set Keyframe.

Move the time slider to frame 25. Click drag with your ] in the viewport to squash the rocket. A negative value for strength will create a squash effect. Click with your \ on the Strength parameter and select Commit Change. This sets a second keyframe.

Move the time slider to frame 30. Click drag with your ] in the viewport to unsquash the rocket. A value of about 0.1 for strength will create a slight stretch effect which will suit the rocket as it lifts off. When you are ready, click with your \ on the Strength parameter and select Commit Change.

Playback the results. Edit the animation curves if you want to adjust the inbetween motion. When you are finished press the u key to go back to the object level and test the playback here. You may want to adjust the animation curves of the rocket’s translate Y to make the lift-off more snappy. The quality of the motion is under your control.

3. Animating the Camera

To animate the camera to always look at the rocket, you simply have to point the camera at the rocket. Click on the object operator for cam1 in the Network editor, and set the Look At parameter to: rocket.

Playback the results. The camera now follows the Rocket as it takes off.