FXPHD – HOU221 – USD and LOPs for Houdini Artists

本课程专为希望熟悉 USD 的工作原理以更好地了解他们正在工作的管道的艺术家而设计。它将涵盖您需要了解的有关 USD 的所有基础知识，然后将更多地关注 Houdini 和它在 18.0 版本中引入了新的 LOP 上下文，允许艺术家在程序上编辑和创建 USD 文件。

本课程首先解释 USD 的所有核心概念，然后将这些知识应用于示例镜头，因为它沿着基于 USD 的管道移动。它将涵盖资产创建、布局、动画、FX 和照明。最后，您将对 USD 管道从头到尾的样子有一个深入的了解，尤其是如何在 Houdini 中处理 USD 文件。将涵盖作为 Houdini 艺术家从打开USD文件到将其导入 SOP，然后成功将其导出回USD所需的一切。

第 1 课：USD数据结构第 1 部分
我们将重点介绍USD的基础知识，重点是数据的结构，并介绍 LOP 作为创建和编辑USD数据的地方。还将介绍我们将在整个课程中开展的项目。之后，我们将开始介绍一些USD术语，例如 Prim、Schema、Namespace、Properties、Attributes、Relationships 和 Metadata，同时学习如何在 Houdini 中查看所有这些东西。本课以一个小示例结束，说明如何将 SOP 中的模型导入 LOP 时转换为 Prims 层次结构。
第 2 类：USD数据结构第 2 部分
继续上一课的示例，本课将涵盖与属性相关的所有内容。我们将讨论属性类型、原始变量、插值以及默认和时间采样值。视频的最后一部分将介绍图层的概念，我们将学习如何从 Houdini 导出 USD 文件以及 usda 和 usdc 格式之间的区别。最后，我们将打开 USD 文件并学习如何读取其内容。
第 3 类：USD构成第 1 部分
现在我们已经很好地理解了 USD 如何构建 3D 数据，我们将看看 USD 的合成引擎如何允许我们组合不同的层。合成是 USD 的一个关键功能，它允许您将资产组合成聚合体，并让不同的艺术家和部门对它们进行非破坏性编辑。在本课中，我们将回顾舞台的概念并查看称为子层和参考的两个主要构图弧，并学习如何在 LOP 中构建这些构图。我们将完成这节课，涵盖说明符及其在组合方面的重要性。
第 4 类：USD构成第 2 部分
在第二部分中，我们将介绍其余的组合弧：有效负载、变体集、继承和专门化。我们将通过一个小例子来展示这些组合弧是如何在整个管道中使用的。视频的第二部分将重点介绍 LIVRPS 和了解组合弧的强度排序。最后一个概念非常重要，也是最难理解的概念之一。
第 5 类：创建资产第 1 部分
我们终于准备好开始创建我们将在项目中使用的资产。在这堂课中，我们将应用我们在前几节课中学到的所有概念，以提出我们将使用哪些组合弧和层来构建每个 USD 模型。我们将深入了解 LOP 的工作原理，学习如何一次处理和导出多个匿名层，以及涵盖 Default Prims 的概念、将属性放样到有效负载、分配材料，最后我们首先看看 Karma 看看我们的材料是什么样的。
第 6 类：创建资产第 2 部分
在本课中，我们将使用用于从第 5 类创建资产的设置，并使其更加程序化，以便我们可以轻松地将其与所有其他资产重用。我们将在我们的项目中检查 6 种不同的资产，它们的设置都有细微的变化，例如多个模型变体或模型和材料变体集。我们还将介绍更多概念，例如子集、模型层次结构和目的。本课程的最后一部分将介绍 5 种不同的方式来构建资产。
第 7 课：布局和动画
通过查看如何组装镜头，我们将继续学习并更加熟悉 LOP。我们将了解舞台管理器以及它如何帮助我们快速加载资产以组装场景，它与交互式编辑一起允许我们将这些资产放置在我们的场景中。在本课中，我们还将介绍 Viewport Overrides、Instancing 并研究将动画和布局的编辑构建到它们自己的层中的两种方式。
第 8 类：USD外汇第 1 部分
在本课中，我们将介绍 FX 艺术家工作流程的第一部分，从在 LOP 中加载动画到将其导入 SOP。为了实现这一点，我们必须了解 LOP Import 和 USD Unpack 以及如何遍历阶段并导入我们想要的内容。该工作流程的一个组成部分是 usdxform 属性，因此我们将了解世界和本地空间及其在 LOP 和 SOP 之间往返时的重要性。最后，我们将把 FX 层写成一系列文件，并学习如何将其拼接成一个值剪辑，以便 USD 正确读取它。
第 9 类：USD外汇第 2 部分
在 FX 工作流程的第二部分，我们将学习 Primitive Patterns 和 Vexpressions，以便在舞台中轻松选择 Prims。我们还将把 Collections 视为一种轻松分组 Prims 的方式，以便以后可以将它们导入 SOP。本课将重点介绍卷以及如何将 VDB 导入 LOP，最后介绍 RBD Destruction LOP，当我们进行 RBD sim 时，这是一种让 LOP 处理所有USD方面的非常方便的方法。
第 10 类：USD外汇第 3 部分
本课程将涵盖剩下的两个效果，即相框掉落和书籍的 RBD 模拟。我们将学习如何手动将打包几何导入 LOP，而不是像以前那样使用 RBD Destruction LOP。对于几何结构没有改变的书籍，我们将介绍如何只创作书籍模拟的变换而不实际修改任何 Mesh Prims。
第 11 课：照明和渲染
为了结束我们的示例，我们将回顾管道中涉及照明和渲染的最后一个阶段。在本课中，我们将了解以 USD 为单位的灯光以及如何在 LOP 中实现这一点。我们将介绍如何使用 Light Mixer、Light Linker 以及如何在不更改原始图层的情况下编辑现有材质。最后，我们将看看 Houdini 的新渲染器 Karma。我们将介绍基本设置以及使用 Light Path Expressions 为每个灯光创建自定义组件 AOV。
第 12 类：高级 LOPS
在本课程的最后一课中，我们将学习一些本课程未涵盖但值得了解的高级技巧和窍门。我们将首先看一下 USD 附带的两个工具，它们称为 usdcat 和 usdview，然后看一下 Instancer LOP 以及如何使用它以程序方式创作组合弧。我们将研究的另一个技巧是 HoudiniLayerInfo Prim 以及我们如何使用 Store Parameter LOP 临时存储数据。最后，我们将了解 Python LOP 以及如何创建 Loft Variant Set HDA。

Duration 5h 45m Project Files Included MP4

Title: FXPHD – HOU221 – USD and LOPs for Houdini Artists

Info:
More and more applications are starting to support USD and most studios are in some way using it in their pipelines. USD is here to stay and it is slowly becoming the industry standard. This course is designed for artists who want to get familiar with how USD works to better understand the pipelines that they are working in. It will cover all the basics you need to know about USD in general, and then it will focus more on Houdini and its new LOP context introduced in version 18.0 which allows artists to procedurally edit and create USD files.

The course begins by explaining all the core concepts of USD, followed up by applying this knowledge on an example shot as it moves along a USD based pipeline. It will go over asset creation, layout, animation, FX and lighting. In the end, you will have a solid understanding of what a USD pipeline looks like from start to finish and especially how you can work with USD files in Houdini. Everything you will need as a Houdini artist from opening USD files to importing them into SOPs and then successfully exporting it back to USD will be covered.

CLASS 1: DATA STRUCTURES IN USD PART 1
We are going to look at the very basics of USD with a focus on how data is structured, as well as introduce LOPs as the place to create and edit USD data. There will also be an introduction to the project we are going to be working on throughout the whole course. Afterwards, we will begin to cover some USD terminology such as Prim, Schema, Namespace, Properties, Attributes, Relationships and Metadata, while learning how to view all these things in Houdini. This lesson finishes with a small example of how a model from SOPs can be converted into a hierarchy of Prims when imported to LOPs.
CLASS 2: DATA STRUCTURES IN USD PART 2
Continuing with the example from the previous class, this lesson will cover everything related to attributes. We are going to go over attribute types, primvars, interpolation and default and time sampled values. The last part of the video will introduce the concept of layers and we are going to learn how to export USD files from Houdini and the differences between usda and usdc formats. We will finish by opening the USD file and learning how to read its contents.
CLASS 3: USD COMPOSITION PART 1
Now that we have a good understanding of how USD structures 3D data, we are going to look at how USD’s composition engine allows us to combine different layers. Composition is a key feature of USD which allows you to assemble assets into aggregates and let different artists and departments non-destructively edit them. In this lesson, we are going to go over the concept of stage and look at the two main composition arcs called Sublayers and References and learn how to build these compositions in LOPs. We are going to finish this lesson covering Specifiers and their importance when it comes to composition.
CLASS 4: USD COMPOSITION PART 2
In this second part, we will cover the remaining composition arcs: Payloads, Variant Sets, Inherits and Specializes. We will go over a small example that shows how these composition arcs are used throughout the whole pipeline. The second part of the video will focus on LIVRPS and understanding the strength ordering of composition arcs. This last concept is very important and one of the trickiest to understand.
CLASS 5: CREATING ASSETS PART 1
We are finally ready to start creating the assets we are going to be using in our project. In this class, we are going to apply all the concepts we learnt in the previous lessons to come up with what composition arcs and layers we are going to use to structure every USD model. We will go in-depth over how LOPs works and learn how to handle and export multiple anonymous layers at once as well as cover the concepts of Default Prims, lofting properties to a payload, assigning materials and finally having our first look at Karma to see what our materials look like.
CLASS 6: CREATING ASSETS PART 2
In this lesson, we are going to use the setup used to create an asset from class 5 and make it more procedural so we can easily reuse it with all the other assets. We will go over 6 different assets in our project which all have slight variations in their setup, such as multiple model variants or a model and a material variant set. We are also going to cover a few more concepts such as Subsets, Model Hierarchy and Purpose. The last part of this class will go over 5 different ways in which you could structure your asset.
CLASS 7: LAYOUT AND ANIMATION
By looking at how we can assemble a shot, we are going to keep learning and getting more familiar with LOPs. We will look at the Stage Manager and how it can help us quickly load assets to assemble the set, which together with the Interactive Edit will allow us to place these assets in our scene. In this lesson, we will also cover Viewport Overrides, Instancing and look into two ways in which the edits from animation and layout can be structured into their own layers.
CLASS 8: FX IN USD PART 1
In this lesson, we will cover the first part of the workflow of an FX artist, from loading animation in LOPs to importing it to SOPs. In order to achieve this, we will have to learn about the LOP Import and the USD Unpack and how to traverse the stage and import what we want. An integral part of this workflow is the usdxform attribute, so we will go over world and local space and its importance when roundtripping between LOPs and SOPs. Finally, we will look at writing out the FX layer as a sequence of files and learn how to stitch it into a value clip in order for USD to read it properly.
CLASS 9: FX IN USD PART 2
In the second part of the FX workflow, we are going to learn about Primitive Patterns and Vexpressions to easily select Prims in the stage. We will also look at Collections as a way of easily grouping Prims so they can be imported into SOPs later. This lesson will focus on volumes and how VDBs can be imported into LOPs and finally an introduction to the RBD Destruction LOP which is a very convenient way of letting LOPs take care of all the USD side of things when we do an RBD sim.
CLASS 10: FX IN USD PART 3
This class will cover the two remaining effects which are the picture frame falling and an RBD simulation of the books. Instead of using the RBD Destruction LOP as before, we are going to learn how to import packed geometry into LOPs manually. In the case of the books where the geometry hasn’t changed, we are going to cover how we can only author the transforms of the book simulation without actually modifying any of the Mesh Prims.
CLASS 11: LIGHTING AND RENDERING
To end our example we will go over the last stage in our pipeline which involves lighting and rendering. In this lesson, we will learn about lights in USD and how this is implemented in LOPs. We will cover how to use the Light Mixer, the Light Linker and how to edit existing materials without changing the original layer. Finally, we will look at Karma, Houdini’s new renderer. We are going to cover the basic settings as well as creating custom component AOVs per light using Light Path Expressions.
CLASS 12: ADVANCED LOPS
In the last lesson of this course, we will look at a few advanced tips and tricks that weren’t covered in the course but are worth knowing. We will begin by taking a look at 2 tools that come with USD which are called usdcat and usdview, followed by a look at the Instancer LOP and how it can be used to author composition arcs procedurally. Another tip we will look into is the HoudiniLayerInfo Prim and how we can temporarily store data using the Store Parameter LOP. Finally, we will learn about the Python LOP and how to create the Loft Variant Set HDA.