Getting procedural
The procedural paradigm may sound like a scary word, it just means that you don't focus on objects ( either geometrical or pictures or anything) but on functions which are here called Operators. Object may change but the core of your workflow is a network of operations. It requires that you think your scene rather than simply doing it, but once this effort is done, Houdini drastically reduces the distance between your ideas and your work . Here we take you smoothly, with a perfectly coherent set of examples, to bend your mind to this new paradigm you won't ever leave once you tasted it.

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Houdini Apprentice OR MASTER
All the video has been made with the Apprentice version of Houdini, which is FREE and UNLIMITED( it just has render size limitation, and of course don't forget to renew your free licence every month :) ). This means, there's no need to work at ILM or Pixar, on overpriced SGI super calculators.
Just anyone can learn real and serious 3d.
Of course the final renders and the files are in .hip , .otl format which are perfectly usable with both commercial and non-commercial versions of Houdini.

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Using VEX in VEX Cops
This first step intend to make you think of Houdini COPs and VEX COPs not as a simple compositing tool but a procedural pattern generator.
The functionality of VOPs let you design VEX functions without writing the code! The mix of VEX functions ( which are punctual and Compositing Functions ( which are global) allow you to generate a infinite diversity of interesting patterns. Here we focus on cellular patterns.
This approach is more flexible to create, once vectorized, interesting 3d flat object with cool patterns.

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Procedural Modeling
Procedural paradigms in visual effects applications have never been more popular. Houdini nearly set the trend in this type of work flow over a decade ago. We take you through a variety of tools to help you construct models that can be altered without destruction after your first revision. In a non-procedural modeler, this could permanently alter your model beyond easy repair. You can also take advantage of instancing parts of a model to be used in more than one location on the parent geometry.

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Procedural Shading (Instancing)
We introduce you to both the procedural texturing of your object: if your object is defined procedurally, you need to texture it accordingly, in a way where if the geometry changes, the texture updates. We intensively use procedural Group definition and layer of UV attributes. We introduce you to the writing of simple shaders, the shader becoming a parametrable "object" . So we take you to the process of instancing shaders: this means you will use the same shader with different parameters ( for example different textures) for each object he's applied to. This is necessary to create a diversity of building with different wall textures, different roof textures, window, door textures you can control on each . This is important when you create fully detailed digital asset. We present advantages and inconvenient of including shader definitions in your digital assets.

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Copying Operations
One of the keys to proceduralism is a clever use of the instancing/copying options. Here we use copying operations to instance geometry, instancing Digital Assets and controlling copies parameters with expressions, with attribute maps etc.
But also in a non-standard way to divide-and-solve modeling problems.
This is much more than a trick, it's a method that you can convert in thousand of tricks!
This is achieved with an intensive use of the Copy SOP , the Delete SOP and some expressions and can tackle down many if not most modeling problems. Remember that Houdini is also like programming without any code!

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Creating Digital Assets
Digital assets are custom operator types built from node networks. They are some sorts of macros that can encapsulate any type of Operator, any part of network in a digital asset, and then "promote" parameters from nodes inside the asset up to the « public level » as parameters of the asset itself. You can really think of them as classes/objects if you're familiar with object-oriented programming.
Digital assets let you capture the functionality of any network... a character, a compositing effect, a particle system, ANYTHING you can imagine and turns it as a reusable tool. This provides incredible flexibility.
We introduce you to the creation of the digital assets through very concrete examples.

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Organizing your workflow
Creation of a fully detailed city requires to handle a big workflow. Our approach is to divide it in key steps:
on one side the creation of the city pattern, the refinement to the level of individual building sites. This separation means that someone ( the map creator) in your studio can focus on the creation of detailed and rich city maps. Meanwhile another person, specialist of architectural types creates buildings that the map creator can place wherever he wants making attributes vary according to demographic facts or statistical information's without knowing anything about how the building creator shaped his building. He just uses the building as a single operator (a HDA).

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The creation of the generic building.
This separation means that someone in your studio can focus on the creation of a detailed and rich city structures. Meanwhile another person, specialist of architectural types create building that the first user can place wherever he wants making attributes vary according to demographic facts or anything. With OTL creation, the map designer don't need to know anything about how the building creator shaped his building. He just use the OTL as a single operator.
The interest is to show you how managing your workflow helps you to have better flexibility, control and productivity.


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Software, Source and the Tutorial
If you think of Houdini's Operator Types Libraries (OTLs) as Classes in Object-Oriented Programming (without any programming of course !) we give you the software, the source, and the tutorial).
Thanks to our special video format we provide you with the scene files used to make this tutorial (plus the HDA/OTL files). Our high definition video makes it seem like you are doing the work on your own computer.




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Contents
We give you some knowledge about procedural modeling of cities, ( the tutorial) but we provide you with
a fully functional and ready to use City-generator that you can use straight ahead in production to create your own urban environments ( the software).
You can of course modify the content of the digital assets ( the "software" is open-source) and create new kinds of cities, even more complex, even more detailed, even more spectacular.


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The Author
David Gary is 25 years old, french, and has a Bachelor Degree in Pure Mathematics, a Master Degree in Philosophy and is preparing his PhD in the interdisciplinary field of philosophy of mathematics, phenomenology and cognitive sciences. Aside of his studies, he's directed a dozen of short movies and video clips, being a director/video instructor. He began to be a strong CG specialist since a long time using various tools as 3dsmax, Maya, Houdini. He's been a Maya Teacher in a french studio and is now a advocate of Houdini and its procedural paradigm.

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