Let's get started

To get started, will start to understand where can you write and store your tools.

Houdini Folder Structure

Houdini reads the user preferences and fetch HDA, presets and other user defined tools from the various paths defined in the environement variable `HOUDINI_PATH`.

As multiple folder are allowed here, this allow multiple packages to implement their own set of files which then will be loaded/merged by Houdini. Houdini will automaticly create one of those folders, with various files in it, at startup.

• [houdini] - The root folder can be name as you wish. This is the path that need to be added into `HOUDINI_PATH` environement variable.

  • config

    • Icons - where to palce custom icons
    • NodeShapes - where to place custom node shapes

  • desktop - User defined desktop
  • gallery - User stored gallery files
  • otls - where to put HDA/OTLs
  • packages - where to install houdini packages
  • presets - store node value presets
  • python_panels - store user defined custom Qt interfaces

  • scripts

    • python - store python scripts
    • ... - store user hscript and commands

  • toolbar - store shelves and tools

Most of the tools and scripts you will be implementing will match this structure.

Environment

Environment variable used to be tradionally set in a file name `houdini.env`, though it is now recommended to use Houdini Packages as describred bellow.

Here are some environement variables that are worth knowing:

Read more: Houdini Environment Variable Documentation

Houdini Packages

Houdini Packages allow to separate and organize files into packages that can be indivudually managed. In addition, packages can be used to define environement variables. Packages can be used at studio or user level.

A package is defined by a json file and a houdini config like folder. I recommend placing those file and folder in a directory that is referenced by the environement variable `HOUDINI_PACKAGE_DIR`.

Here is the content of the json file I use for most of my packages:

{
    "hpath": "/path/to/the/package",
    "load_package_once": true
}

Then follow the folder structure as described earlier for `/path/to/the/package` content.

Read more: Houdini Packages Documentation

Tool Creation

Let's open Houdini and start to create our first tool.

We will start by creating a new shelf that will be used to store our tools.

Tools are scripts that can be triggered from various places in Houdini. A common place to store them is on a Shelf. Shelves is any easy way to create and organize tools while keeping them easiliy accessible to sue. Shelves are added to ShelfSets, which are collection of Shelves. Houdini come with a huge collection of ShelfSets, Shelves and Tools.

print("Hello World")

<?xml version="1" encoding=""UTF-8>
<shelfDocument>
    <tool name="my_tool" label="My Tool" icon="PLASMA_App">
        <script scriptType="python"><![CDATA[print("Hello World")]]></script>
    </tool>
</shelfDocument>

<?xml version="1" encoding=""UTF-8>
<shelfDocument>
    <!-- This is where a ShelfSet is defined and what shelves it contains. -->
    <shelfSet name="my_shelf_set">
        <!-- You can add more shelves before -->
        <memberToolshelf name="my_shelf"/>
        <!-- and after! -->
    </shelfSet>

    <!-- This is where a Shelf is defined and what tools it contains. -->
    <toolshelf name="my_shelf" label="My Shelf">
        <!-- You can add more tools before -->
        <memberTool name="my_tool"/>
        <!-- and after! -->
    </toolshelf>
</shelfDocument>

Creating Menu

Similarly to tools, tools/scripts can be invoked from menu. Menu files are stored at the root of the folder structure. Menus cannot be edited from code and usually require restarts to be refreshed.

Each Houdini menu has it's own speficic file for the menu that define it. Here are some of the most common menu you would come to edit:

• MainMenuCommon.xml - control the main window menu
• OPmenu.xml - control the menu when you right click on a node
• PARMmenu.xml - control the menu when you right click on a parameter
• ParmGearMenu.xml - control the "Gear Menu" in the parameter interface

I invite you to read more about menu with the official documentation.

Example of menu:

<!-- MainMenuCommon.xml -->
<?xml version="1.0" encoding="UTF-8"?>
 <mainMenu>
   <menuBar>
     <subMenu id="my_submenu">
       <label>My Submenu</label>

       <scriptItem>
         <label>My Tool</label>
         <scriptPath>$HOME/scripts/my_tool.py</scriptPath>
       </scriptItem>
     </subMenu>
   </menuBar>
 </mainMenu>

Next Chapter

In the next chapter, we will start looking into Houdini Python API.