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Introduction to Houdini

1 GETTING STARTED: ROLLERCOASTER TOUR

The basic principles underlying creating 3D graphics on a computer are very similar no matter which program you might be using. Essentially, the artist must use the interface provided to communicate with the program what elements should be created and how they should behave. This communication enlists a combination of math, physics, computer programming, and many other inputs that let the artist, via the program, tell the computer what to create. Houdini's architecture is built around the concept of procedural animation. The software evolved out of production over fifteen years, with the idea that no matter what the project, there are always more changes to be made and this consideration must be a part of the process. This tour is an introduction to this method of working in Houdini. Once you've grasped this fundamental approach, the rest should flow nicely.

1.1 OPERATORS, PARAMETERS AND VIEWERS

In Houdini, you build all of your information with a method of building networks of operators, that are represented as nodes. Houdini provides you with an interactive worksheet for building these flow charts or trees of operations and the ability to see the result of each operation at any time in the viewer. To illustrate the discussion, we're going to use the finished rollercoaster file as an example. Locate the final_rollercoaster.hip file and double click on the icon to open. You should see the following on your screen:

Operators Viewer

Operator Parameters

You may have heard Houdini artists speaking OPs. These terms, SOPs, CHOPs, COPs, etc., refer to this method of working with operators and parameters. Whether you are setting up a scene, creating a particle system, or compositing images, in Houdini you can always manage the task with this method of operations.

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1.2 COOKING

Each operator has a set of parameters that can be modified at any time. As Houdini scrolls through the frame range, it processes the information stored in each and every operation that is linked into the network, calculating and building the result at that frame. This process of calculating the information over time (or as each frame passes) is called "cooking".

Cooking in Houdini

1) At each frame 2) Houdini "cooks" all the parameter information of all the operators 3) Based on the information in the operator networks, Houdini creates a visual result in the viewer

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The value in this system is that until you render your scene, all of the parameters are essentially alive, waiting to be processed in the cooking. This means you can go back and make changes throughout the process, allowing for flexibility, experimentation, and the ability to deal with the reality of constant changes that usually happen in production.

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1.3 OBJECTS EDITOR

This editor is the final stage where all of your elements are placed, and the lights and cameras are set. Other tasks in the object editor include character, atmospheric and rigid body dynamic setups. If you take a look at your object nodes, notice the different objects. You've got a few cameras, lights, and the various items that make up your scene, such as the coaster track and the coaster car.

NAVIGATING

Notice the interface is currently divided into three panes. At the top left hand corner of each pane is an icon representing the type of pane it is. (For a further introduction to this aspect of the interface, see next HOUDINI_HELP.pdf.)

At the upper left hand corner of each pane is an icon indicating the pane type

For now, locate the icon and corresponding panes, and try out the following navigation tips. 1. To move your cursor around in the viewer, hold down your Wand [ ] \ keys.

In the viewer pane:

W = View Mode W [ = rotate W ] = dolly/zoom W \ = track

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2. Now, hold your cursor over the network pane, and use your ] \ keys.

In the network pane:

] = dolly/zoom \ = track

3. Now, zoom in and locate the operator node called coaster_car. Place your [ directly in the middle of the node and click to select the operator. Notice the green highlight showing the operator is the currently selected node, and the yellow highlight shows it is selected. (Other selected nodes will have the yellow highlight as well.)

[ click in the middle of the node to select.

The green highlight indicates the currently selected node. The yellow highlight indicates the node is selected.

4. Notice when you selected the coaster_car operator, its associated parameters show up in the linked parameter window.

The selected object's parameters show up in the parameter pane Notice the parameters deal with object transformation allowing you to place the object in the scene. Additional folders deal with shading, rendering, and physical properties for Rigid Body Dynamics.

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5. To adjust the parameter values, you can double click in a parameter box and type in a value. You can also \ click to undo the last update.

Double click to type in a value:

\ click to undo the last update 6. Type the T key to jump to the next parameter box. 7. You can adjust the values with the interactive slider by ] clicking in the parameter box.

] click in the parameter box

to get the slider ladder. Drag up or down to choose the amount by which you'll adjust the slider. Drag right for positive, left for negative.

8. Locate the Position parameter and notice it is colored, and all the other parameters are not. This indicates that there is a channel existing in that parameter. If no channel exists in a parameter, the given value will remain constant throughout the frame range. Green indicates there is a keyframe on the current frame, cyan indicates the channel, but no keyframe.

Color in a parameter box indicates an animated channel. Green = keyframe on channel Cyan = channel but no keyframe

9. [ click to the left of the position parameter. You should see the parameter toggle from the numeric value to an expression. Adding expressions to a parameter is as easy as typing it in, and Houdini lets you toggle between the numeric and

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expression values.

[ click to the left of the parameter = lets you toggle between numeric and expression values 10. Locate the playbar at the bottom of your screen. Select the playback button and watch the animation. You can toggle between numeric and expression values in the Position parameter to see the numeric value change.

You can also scrub through the frames by dragging the slider.

Select the Playback key to view the animation.

11. You can view through the different cameras and lights in the viewer by selecting them from below the viewer. Notice that once you W [ ] \ in the viewer, the size of the viewer jumps away from the camera aspect ratio and the view is indicated as "no camera".

Select a camera through which you can view the scene.

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1.4 OBJECT SPACE: ALL THE WORLD'S THE STAGE

In Houdini, creation tasks are divided into the different editors where the tools for that type of creation are accessible. Though you're always still working with operations, parameters and viewers to see, the list of operators and types of parameters will change depending upon the editor in which you may currently be working.

The different editor types in Houdini offer the viewers and operators that correspond to that type of creation.

The object editor = World Space for placing, lighting and viewing the elements in your scene.

The Object editor can be considered "World Space". It is here that you can place the elements in your scene, with lighting and cameras. As was mentioned above, the object parameter folders of all objects generally deal with issues of placement (the transform folder), shading, and rendering. 1. Click to select a camera object and notice the difference in the parameters offered from those of the basic object parameters.

Select a camera object. Notice all the parameters have to do with camera type operations: (View, Crop, Roto, etc.)

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2. Now select a light object. Notice the parameters deal with lighting.

Select a light object. The parameters all have to do with lighting.

So where does the actual modeling of geometry happen? For this, Houdini takes you "inside" of each object to create in "local object space" vs. "world space". This editor is called the SOP editor, or Surface Operations. This is where you'll find all of the operators that deal with modeling and creating surfaces. Once you've added a new object into your scene at the object level, you can then "enter" the object to access all of the SOP tools.

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1.5 THE SOP EDITOR: LOCAL OBJECT SPACE

To take a look at the SOP editor, you must select an object and then go inside of it at the SOP level. 1. Locate and select the path object in the network view. From the top of the pane menu, select the arrow to "enter" or "jump down" into the object.

1) Select the 'path' object 2) Select the arrow to `jump down' into the object to the SOP editor.

2. You should see the interface change. The blue coloring of the top menu changes from blue to green. The network contents change from object nodes to SOP nodes. The parameter pane switches to correspond to the currently selected SOP node.

The color changes from blue (objects) to green (SOPs).

The network contents show each operator that creates the `path' object, and the parameters correspond to the currently selected SOP.

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3. Notice the viewer pane didn't change with the other panes. This is because the viewer pane is not linked to the others. Find the circle in the upper right hand corner of the viewer pane, and assign it to number 1. The pane is now linked to the others, and you'll see the viewer pane will switch accordingly.

Select 1 to link the viewer pane to the other panes (which were already set to 1)

4. The scene in your viewer may not be the same as mine in the above image. Because you've "entered" into the local object space, you are able to view that object isolated, or also with all the other objects in the scene. In other words, there is a button to toggle between the world view, or the local object view.

Toggle between local/world view `see one/all'.

You can also select and interact with the other objects in the scene, even when in local mode, however, you can \ click on the button to activate world selection. A yellow highlight will appear around the `see one/all' button when selecting from all objects is on.

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5. Now you should just see the path object by itself. Type W h to home your view on the path object.

6. Now you can [ click directly in the middle of each operator and view its corresponding parameters. Notice the changes of the different parameters for the various tools.

The parameters change according to the selected and corresponding operator (or tool).

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7. Now you can navigate around and jump into the other objects and take a look at their contents. Select and take a look at the different objects in the scene from the menu above the panes.

[ click on the object name

and select other objects from the menu The panes will switch to jump into the selected object.

1.6 POPS: PARTICLE OPERATIONS

Now that you have been introduced to working with OPs, params and viewers, and you have a feel for navigation, we'll take a quick tour through the rest of the editors in Houdini. From the menu above the panes, switch from SOPs to POPs.

Switch from SOPs to POPs.

As you may have guessed, POPs stands for particle operations. Here you have all the tools you need to generate particle simulations. These particles are used to create many kinds of effects that simulate natural phenomena such as rain, smoke, and dust. Even though you must switch into the POPs editor to generate the simulation, you'll find that the whole system is integrated. This means that you can generate particles from and have them interact with any objects in your scene.

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1. Take a look at the POPs interface. Look familiar? You've got a viewer, a network pane with your operators, and a parameters pane. In this case, the viewer lets you see guide geometry that either represents the objects from your scene that you may be using to birth particles, or the actual guides that represent the POPs you might be using.

POPs = Particle Operations

Operator Viewer

Operator Parameters

1.7 SHOPS: SHADER OPERATIONS

1. Now switch from POPs to SHOPs. (We'll skip over Materials and TOPs as these are older editors and newer editors for creating materials have begun to replace them.) SHOPs stands for shader operations. Here you can load in and manipulate Houdini shaders, which are written with VEX (Vector expression language), and can be rendered with Mantra, Houdini's renderer, or even Renderman shaders (to be rendered with Renderman). If you have not and are not going to be writing shaders, there is a library of existing shaders from which you can choose, and you can even load in shaders downloaded from the internet.

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SHOPs = Shader Operations

Viewer Operators

Operator Parameters

2. Once again we have the viewer, operators and parameters. The difference here, is that the viewer gives you a preview of the shader you've selected. Notice in the network pane, instead of nodes the shaders are in a list. In any of the network panes, you can always toggle between node and list mode by typing t in the network pane.

t toggles between list and node display of the operators in any network pane.

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1.8 CHOPS: CHANNEL OPERATIONS

Now switch into the CHOPs editor. Here you can create and edit channels.

CHOPS = Channel operations

Viewer

Operators

Operator Parameters

The channels may be created here from scratch, as there are certain CHOPs that simply create certain types of channels, such as the wave CHOP that creates a channel with a sin wave, for example, or the noise CHOP that creates a noisy channel. You can then send these channels out to any parameter anywhere in Houdini, so that the channel you cooked up here is driving the motion of an element in your scene. You can also fetch channels from any parameter in Houdini, tweak them by squashing or stretching them, for example, and then send them back out. Once again, the viewer is for viewing the channels, in this case, and then you've got the operator network and parameters panes.

1.9 COPS: COMPOSITING OPERATIONS

Built into Houdini is also a compositor. In fact, there are currently two versions of the Houdini compositor. For now, the older version is still present as COPs V2 is still in beta. Because the compositior is integrated, you'll find you can use it for many additional tasks you might not have imagined. For example, you can use COPs to adjust texture maps. Once again, the viewer is for viewing the current COP

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and there are the COP network and parameter panes.

COPs = Composite Operations

Viewer Operators

Operator Parameters

1.10 ROPS: OUTPUT OPERATORS

Last, but definetely not least, is the output editor where you can set up and modify all kinds of output operators to render your scene. In this case the viewer lets you see the current renders and suspend or kill those processes.

COPs = Composite Operations

Viewer

Operators

Operator Parameters

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There are many different output options including rendering with Mantra, Houdini's renderer, or outputting to Mental Ray or Renderman. Rendering out geometry per frame and Wren, a 2D renderer are also options.

1.11 CONCLUSION

That is the whirlwind introductory tour of Houdini. Now you should have a feel for the way things come together and are created, and a feel for moving around in the interface. The next exercise introduces you to panes and desks, and how to set up and arrange the interface in Houdini. Go ahead and close the file by selecting Quit Application from the menu in the upper left hand corner.

1) From the file menu

3) Select Discard & Quit 2) Select quit application

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