'The Magic of Houdini': The Three Most Common Panes

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.

By default, Houdini is arranged in three panes the Viewer pane, the Network Editor pane and the Parameters pane. Figure 1 shows each of these areas. The Viewer pane is where you control the viewport and can change how things are displayed. The Network Editor pane shows you a node-based view of what your networks look like. Each of the boxes in this pane is considered a node (or tile). The Parameters pane shows you the specific information about a particular node.

A pane is a generic window that you can configure to display a number of different types of information. The Network Editor pane could just as easily be set it to show parameters (in which case it becomes the Parameters pane) or the view into 3D space (in which case it becomes the Viewer pane).

To change the pane type, just click the Pane menu in the upper-left corner of any pane and choose a different type. LMB on the Pane menu in the Viewer pane and choose Network Editor. You now see the same information as in the other Network Editor pane that was already displayed. Now change it to a Channel Editor pane. This pane is used for manipulating animation channels. As you can see, you can configure a pane to display whatever type of information you want. Change it back to a Viewer pane to continue this chapter.

The Viewer Pane

The Viewer pane is where you control the viewport and can change how things are displayed using differing projection methods, different shading modes, as well as determine what kind of geometric information to display, such as point numbers and normals, and much more.

Stowbars

Stowbars are common to all panes and allow you to hide or display the associated contents. If you dont see all the options, as shown in Figure 2, you might need to LMB on a stowbar to unstow the information. Stowbars provide a quick way to maximize screen space by collapsing options you dont need to see.

State Indicator

The state indicator tells you what type of state you are in. No, it isnt a palm reader or a clinical behaviorist, so it wont have much luck in diagnosing your personal state, but it is highly accurate in describing what state you are in within Houdini. Some actions can only be performed in particular states. The two basic categories are View state or an operational state. Adjustments to the viewpoint are made while in the View state, whereas adjustments to a particular operation are performed while in the chosen operational state.

View Indicator

The view indicator tells you which view you are currently using to peer into the scene. You can choose to view the scene through a number of views, including perspective, top, left, back and so on.

Selection Options

This is where you set selection options such as using a mask, choosing secure selection, redoing a selection and more. For example, you can turn on a point selection mask so that your selection is limited only to the points of a piece of geometry as opposed to its edges, faces and so on.

Display Options

This is where you set the display options like the visibility of points, hulls, primitive numbers, and more. For example, you can turn on the display of primitive normals to see whether they are facing in the expected direction.

Viewing Options

This is where you set the viewing options like camera view, shading mode, quick rendering, and more. For example, you can turn on the view of a construction grid if it helped out in lining geometry up to a common ground plane.

Moving the View Around

To have any degree of creative fun and success in your new world, you must first be able to see it and move around in it.

• 1. Start a new session of Houdini and you should see the default box in the Viewer pane. Verify that you are in the View state by looking in the upper-left corner of the viewport (as shown in Figure 2).

2. Now that you see something in the viewport, you can practice seeing different sides of it. After all, it is always a good mental exercise to consider the different sides of a situation.

Use the following mouse buttons to adjust the viewpoint as stated. Experiment with each of these methods to gain an intuitive understanding of what each does. If you happen to lose sight of the geometry, home the view with the h key.

LMB = Tumble (rotate around) MMB = Dolly (move in or out) RMB = Track (move up, down, left or right)

Notice that as you move the viewpoint around, the floating origin in the lower-left corner of the viewport moves as well. This keeps you informed as to how the global axes are oriented, as shown in Figure 3.

X axis = red Y axis = green Z axis = blue

The View State and Operational States

As stated previously, you must first be in the View state in order to change the viewpoint. You can verify the current state with the status indicator in yellow as shown in Figure 4. This will either say View, if you are in the View state, or Operation, whereby Operation is the name of the operation you are currently in. For example, it can say Transform or Polyextrude. So, the very important lesson to remember is that if you are in an operational state (also called a working state because it is doing some kind of work), you cant make adjustments to your viewpoint. Likewise, if you are in the View state, you cant access the operation-specific GUI handles.

If you are in an operational state, you can temporarily go into the View state by pressing the spacebar. While the spacebar is pressed, you will see that the status indicator has changed from a working state to the View state. To go from an operational state to the View state, ensure your pointer is over the viewport and press the Esc key. To go from the View state to an operational state, again ensure your pointer is over the viewport and press the Enter key. Being in an operational state gives you access to the GUI handles. 

Transform Handles

Transform handles give you access in the GUI to moving geometry around using translates, rotates and scales.

• 1. In the Network Editor pane, select the node called box by LMB on the icon area of the node or box-selecting the entire node. You know the node is selected when it is highlighted in yellow. Go into an operational state by pressing Enter. You should see the manipulator handle for the box, as shown in Figure 5. You can also see that you are in an operational state called Geometry.

• 2. Try to move the viewpoint just using the mouse buttons and you will find that you cannot. As stated earlier, thats because you are in a working state. Hold down the spacebar and try again. This temporarily puts you in View state and so allows you to move the viewpoint around.

3. Home the view again. Depending on the particular operation, the GUI handle might appear different. In the Geometry working state, you have access to a translate/scale handle, a translate/rotate handle and a translate only handle. The hotkeys are e, r and t, respectively.

• 4. Toggle on the translate/scale handle and examine the different parts of the handle, as shown in Figure 6.

LMB and drag on one of the interior white lines to translate the box in a particular axis. LMB and drag on the purple box in the center to have the freedom to translate in all three axes at once. You can use Ctrl+Z to undo any changes. By default, Houdini has a very large number of undos.

• 5. LMB and drag on one of the red cones (or arrows) on the outside edges of the handle to uniformly scale the box in all axes. Now LMB and drag on one of the red interior lines just inside these arrows to scale in a particular axis. Now LMB and drag one of the outside red edges of the handle to scale uniformly in two axes. For example, grab the red edge pointed to in Figure 6 and you can scale the box in X and Y simultaneously.

6. Press the r key and you still have access to translation, but now you have access to rotation too. LMB and drag on one of the red curves to rotate in a particular axis or LMB and drag on the red intersections of the curves to rotate freely in all axes.

7. Press the spacebar to move the viewpoint around a bit.

8. Press the t key and you will only have access to translation handles. This handle operates the same in that you can constrain movement to a particular axis or move freely in all three axes at once.

• 9. Finally, press Esc to exit the working state and then home the view.

10. The h hotkey homes the view on all visible geometry. In this case, the view is homed on the box. If you have multiple pieces of visible geometry widely spaced, h pushes the viewpoint back as far as needed to encompass them all. This is just like trying to fit everyone in the frame when taking a group photo. The photographer must keep backing up until everyone is in frame.

The g key homes the view on selected geometry only. Homing on selected geometry is especially helpful when you want to get up close to a particular area of the geometry for a closer look. Homing the view on the selection sets the viewports pivot around that selection and so makes it much easier to maneuver around it to get a better view.

• 11. Ensure that the box node is selected and press enter to jump into the Object. With your pointer over the viewport, press s to go into the Select state. Press the 1 hotkey to use the point selection mask. Now choose one of the corners of the default box, as shown in Figure 7. Press g to home the viewport on the selected point. Tumble the view around to see that the pivot is now centered on this selection. This makes it easier to examine particular areas in detail.

12. It is also possible to frame the view, which achieves a slightly different goal than homing it. Press u to jump back up to the Object level. Dolly out a bit and tumble the view. Make sure you are in the View state and press f to frame the viewport. Notice the difference between framing and homing the view. Figure 8 shows the difference between the two methods. You can use Shift+F to frame the current selection, just as you can use g to home the current selection.

Find out more about how to apply each of Houdinis features to your projects as you take on modeling, character animation, particle effects animation, dynamic simulation animation, shading, digital asset creation and rendering. The Magic of Houdini by Will Cunninham. Boston, MA: Thomson Course Technology, 2006. 355 pages with illustrations. ISBN: 1-59863-082-2 ($49.95). Check back to VFXWorld frequently to read new excerpts.

Will Cunningham began his trek by studying both traditional art subjects and 3D computer software at the Academy of Entertainment and Technology. After his studies, he was hired as a Houdini technical intern by Side Effects, the developers of the Houdini software package. Eager to create effects for the big screen, he then jumped into production with BlackBox Digital on the feature, The Prince and Me. Shortly thereafter, he also began teaching Introduction to Houdini at the Academy and has since taught both the introductory and intermediate Houdini courses. In the fall of 2004, he was awarded a fellowship grant by Santa Monica College to support his efforts in creating this book. Over the years, Will has worked for a number of production studios on a variety of projects, including The Chronicles of Narnia: The Lion, the Witch and the Wardrobe, Open Season and Ghost Rider. Currently, he is enjoying effects challenges and learning opportunities at Sony Pictures Imageworks.