If you have not done so already, download the necessary support files.

In this tutorial, we are once again going to be acting as the “assets” department. In this case we are assembling an asset: a bookshelf full of pots. Whether something like this would be done by the assets department or the layout department depends on the studio, but for the sake of this tutorial, we will say it happens in “assets”.

We will have a brief introduction to the Stage Manager node in this lesson. More details on the Stage Manager will follow in the next lesson.

Please also see the glossary entries on Point Instancers and Instancing.

Remember to save your file often as you work, for example as lops_tutorial_2.1.hip

• Start a fresh Houdini.

• Switch to the Solaris desktop.

  Make sure you can see the Scene Graph Tree in one of your panels.

• Jump to /stage.

  Note

  You can create a LOP network at any level in Houdini, but for the sake of clarity, let’s keep our work in /stage.

  Now we are going to use some of Houdini’s native SOP-based tools to do the instancing. There are a lot of nodes to wire up, so please refer to the image below to see how the network is created.

• Create a Reference LOP. Rename it BookShelves.

  Primitive Path

  /$OS/LeftShelf

  Reference File

  $HIP/LOPS_DEMO_FILES/Library/Assets/BookShelves/BookShelfAsset.usd

  A reference is one of the most common way to load prims into a LOP network.

• Append a Duplicate LOP to the reference LOP. (Note that the node might error until it is completely filled in as below.)

  Separate Source and Destination Primitives

  On

  Destination Primitives

  /BookShelves/

  Duplicate Name

  RightShelf

  Modify Source Primitive

  Source Primitives are First Duplicates

  Translate

  1.5,0,0

  

• Append a Set Variant LOP to the duplicate LOP.

  Primitives

  /BookShelves/RightShelf

  Variant Set

  model

  Variant Name

  BookShelf2

  Note

  Note that we are using CamelCase for the name “BookShelves”. Be sure to be consistent with your cases, in Houdini (and Linux in general), the words “bookshelves” and “BookShelves” are not the same word.

• Append a Null LOP to the Set Variant LOP and call it “SHELVES”. You may want to look at the last image on this page to see if it’s all wired up correctly so far.

  Now we’ll use the Stage Manager to bring some things in to instance on the shelf.

• Create a Stage Manager LOP. Don’t wire anything to it yet.

  • In the Stage Manager’s parameters, click on the green “+” symbol to add a folder. Call this Pots

  • Open the file browser in the Stage Manager and dive down into LOPS_DEMO_FILES/Library/Assets/ClayJars (and Herbs) folders, then drag HerbJarsAsset.usd and ClaysJarsAsset.usd into the Stage Manager under the Pots folder.

• Now we will duplicate these objects and choose a unique variation for each. You will end up with seven unique jars.

  • The easiest way to duplicate is to RMB ▸ Duplicate on the prim in the Stage Manager.

  • Once you have duplicated a prim, choose a unique variant for each one. The easiest way to do this is to LMB choose a variant from the variant column in the Stage Manager.

  Your Stage Manager should look like this when you are finished:

  

  Now that you have the things you want to instance to your shelves, let’s create a collection.

• Append a Collection LOP to the stage manager LOP.

  Collection Name

  StuffToBeInstanced

  Primitive Pattern

  /Pots/*

• Append an Instancer LOP to the collection LOP. Wire it up as seen in the last image on this page.

  Primitive Path

  /BookShelves/Contents

  Prototype Source

  Second Inputs

  Primitive Kind

  Group

  Prototype Primitives

  %StuffToBeInstanced

  • Select the Instancer LOP and hit ENTER to dive inside.

  Note

  The Instancer LOP may error until you have performed the next step.

We now want to create a point cloud onto which we are going to instance our pots. There are many ways to do this, but here is one. There are a lot of nodes to wire up. You can scroll to the end of this tutorial to see how the final node network is wired.

• Create a LOP Import LOP.

  LOP Path

  /stage/SHELVES

  Primitives

  *

• Append an Unpack USD to the LOP import node.

  Geometry Type

  Polygons

  Now we want to save just the area we would like to instance pots to so we can scatter some points on it. We need to create a group, and here is one way of doing it.

• In the viewport, press Space + 2 to move to Top view. Press W to toggle wireframe mode.

• Press ⇥ Tab to open the tab menu. Type group and press Enter to start the Group tool.

  • Press 4 key to enter primitive picking mode.

  • Drag a box around the primitives.

    If you don’t get all the primitives in one go, you can hold ⇧ Shift and drag again to select more primitives.

  • RMB ▸ Accept Selection to finish.

• Append a Blast SOP to the group SOP and blast away all but the group you just created.

  You can see that you have both the top and the bottom of the shelves. Let’s get rid of the bottom.

• Append a Delete SOP to the Blast SOP. We will delete by normals.

  Tab ▸ Normal

  Enable

  Direction

  0,-1,0

  Spread

  50

• Append a Scatter SOP to the delete SOP.

  Force Total Count

  300

  Relax Iterations

  100

  Scale Radii by

  2

  Max Relax Radius

  14

Now we are going to create random values to override the base color, specular roughness and albedo of our pots to give them further random characteristics. In Houdini-speak, we are giving them geometry attributes, in USD-speak, these are primvars.

• Append a Attribute Randomize SOP to the scatter SOP. Rename it basecolor.

  Attribute Name

  $OS

  This makes an attribute called “basecolor” with a random value between 0 and 1 in the X,Y,and Z components. What this means is that if there is a shader attached to these prims, and that shader has a parameter called “basecolor,” it will be over-ridden with this value. Using $OS in the node name makes it so that we can now copy/paste our SOPs and just rename the SOPs to get new, correctly named attributes created.

• Copy and paste the basecolor SOP (or Alt-drag the node) to create a copy. Append the new copy to basecolor. Rename the copy rough.

  Min Value

  .5

  Dimensions

  1

• Make another copy of basecolor, append it to rough. Rename the new copy albedomult.

  Min Value

  .2

  Dimensions

  1

  The Dimensions parameter value of 1 makes these values into floats. If you left this at the default (3), it would make these into vectors. In this case it would do no harm, but the shader expects floats for rough and albedomult, (and converts vectors to floats for you if they are not already floats).

• Append an Output SOP to albedomult. Rename the output node OUT.

  Tip

  You can find out the names of the above shader attributes by hovering over the paramater’s labels in the shader.

• Press MMB on your output node. You should see that the point attributes basecolor, rough, and albedomult. If you RMB on the last SOP in your chain and choose Spreadsheet, you should see random values (in the range you chose above) for basecolor, rough and albedomult.

• Press U to jump back up to /stage again.

We should now see some jars on the shelf. Play with the Seed parameter in the Instancer LOP to get a pleasing distribution.

• Set the following in the Instancer SOP:

  Point Attributes to Copy

  basecolor albedomult rough

  Prototype Source

  Second Input

  Note

  In USD, each model instanced across the points is called a prototype.

  Tip

  Currently all jars and pots are oriented in the same direction. You could modify the N attribute and the up attribute (or just the orient attribute) to change this.

  We have one more thing to do before we save this out as an asset. If you look at the Scene Graph Tree, you will see that in the group “Contents” you have “Prototypes” with an undefined kind. It’s not good practice to do this, so let’s fix it.

• Append a Configure Primitive LOP

  Primitives

  /BookShelves/Contents/Prototypes /BookShelves/Contents/Prototypes/*

  Kind

  Group

  You should now see that “Prototypes” are a group.

  

• Append a USD ROP LOP.

  Layer Metadata ▸ Default Primitive

  /BookShelves

  Output File

  $HIP/tutorials/PackedShelves.usd

  • Click Save to Disk to save

Note you can also append some lights to your LOP chain to preview how this will look rendered. To see a Karma render, choose “Karma” from the viewport dropdown, (the menu that defaults to “Persp”).

You are now ready to move on to the next tutorial! If you want to check the results of your shelf build, use a reference LOP to load in your saved USD, ($HIP/tutorials/PackedShelves.usd) and the one from the demo files, ($HIP/LOPS_DEMO_FILES/Library/Assets/InstancedShelves/PackedShelves.usd).

You can also look at LOPS_DEMO_FILES/BookShelfInstancing.hip to see the finished node network as explained in this tutorial.