All images from The Magic of Houdini by Will Cunningham. Reprinted with permission.

This is the next in a series of excerpts from the Thomson Course Technology book The Magic of Houdini by Will Cunningham. In the next few months VFXWorld readers will learn the basics of the dominant tool that has been used in the creation of some of the most awe-inspiring animation and cinematic effects ever made.

You have set quite a few keyframes by now and you have seen how the computer automatically interpolates the in-betweens. What method is it using to do this interpolation? This information and a plethora of other details can be found in the Channel Editor. This editor is the main tool for visually setting and modifying animation channels. The Channel Editor features three methods for viewing data: Graph, Table, and Dopesheet. You examine the Graph view in the following exercise, as it is by far the most commonly used of the trio. For information about the Table or Dopesheet views, check out the Help documents.

1. Delete any active channels you may have on the object containing the sphere. RMB on the tz field and choose Unlock Parameter, if necessary.

2. Go to frame 1 and set a keyframe in tx. Drag the sphere over to the left side of the viewport.

3. Go to the last frame and set another keyframe. Drag the sphere over to the right side of the viewport. Play the timeline and you again have a sphere that goes from left to right.

4. RMB on the tx field and choose Scope Channels. The Channel Editor pops up with the tx channel scoped, as shown in Figure 1. The term scope or scoping channels simply means that Houdini is placing the chosen channels in the channel editor and the channel list so that you can work on them. Note that the Channel Editor is just another pane type. It can be accessed in the Pane menu as well.

The various zones in the Channel Editor.

The Zones of Utility
There are a few different zones of utility in the Channel Editor. The menus are along the top. The view area (highlighted in red) shows the animation data as curves and keyframes. It contains information about these keyframes and curves at the bottom. In the stowbar to the left, you will find various toggle to control what is displayed in the view area. The channel list area is highlighted in green. The channel group area is left at the default gray color.

The View Area
This area shows keyframes and the curves that connect them. Keyframes are represented as white boxes as shown in Figure 2. Values are displayed running vertically along the left edge of the view area. The timeline is displayed in the purple band running horizontally along the bottom edge of the view area. Display options are in the stowbar to the left of the view area.

1. In the example, you can see that there is a keyframe at frame 1 with a value of around -10 and another keyframe at 240 with a value of around 11. It is very easy to adjust keyframes in the Channel Editor. The vertical line is the time handle. Slide this left and right to adjust when the keyframe will happen. The white box is the value handle. Slide this up and down to change the value at this keyframe. These two handles are exclusive of each other. So, you would not be able to adjust the keyframe in time by grabbing the white box or vice-versa. The white horizontal line is the slope handle. This affects how the curves come into and out of the keyframe. Go ahead and play with these handles to get a feel for how they work.

2. Navigation in the view area is very similar to other viewports in Houdini. RMB to pan and MMB to dolly. A really nifty feature of the MMB is that you can independently dolly in the vertical (value) axis or the horizontal (time) axis. Hold down MMB and drag left and right and you will dolly in and out on the timeline while maintaining the visual scale of the values. Hold down MMD and drag up and down and you will dolly in and out on values while maintaining the visual scale of the timeline. And, of course, you can scale both of the axes at the same time, meaning you don’t have to release the MMB and then depress it again to affect the other axis. Using MMB in this way is a very efficient way of getting the animation information into a format you can use. If you ever lose the channel offscreen or something similar, just press h to home the view on the selected curve or curves. LMB does not adjust the view because there is no tumble capability in a 2D view.