SideFX describes the release of Houdini 20 as "undoubtedly the biggest release in its entire history," not only due to the new features it introduces but also because of the "development directions" it sets for future tools. While the release includes updates across all major toolsets in Houdini, the most significant changes have been made to character effects, rigging, animation, and rendering. Among these, the three new character effects tools are the most comprehensive: an entirely new grooming system, feather system, and muscle system.
The animation tools are in the early stages of development: APEX - a new character rigging artist-friendly toolset and the Houdini animation context introduced in the beta version of Houdini 20.
Rendering comprises a blend of these two methods: the CPU/GPU rendering engine Karma XPU is officially ready for use, but the experimental new Vulkan viewport marks the initial appearance of what will eventually become a new real-time cinematic renderer. While this hasn't led to the immediate introduction of a plethora of new tools, Houdini 20 also marks the beginning of a new phase of development: the integration of machine learning support, which will "touch every fiber" of the software.

In Houdini 20, a completely new set of tools for creating and grooming feathers with GPU acceleration has been introduced for character artists. These new tools allow working directly in the viewport, displaying grooming as a 2D array of feathers that can be individually selected and edited using standard tools. The overall shape of each feather is controlled using guide curves - separate curves for the shaft, contour, and individual parts of the feathers - and can be altered by adjusting attributes or painting texture masks to control these attributes. Additionally, masks can be painted directly on the surface of the groomed 3D character in the viewport, enabling scaling and orienting feathers using a standard brush-based workflow. The GPU-accelerated collision avoidance algorithm handles collisions between feathers, and SideFX claims that the entire toolset is fast enough to enable interactive work. Furthermore, the muscle and soft tissue simulation system in Houdini is now officially production-ready.

Recently, one of the primary development directions for Houdini has been the effort to make core tools more accessible to less technically inclined artists who find working with nodes cumbersome. In Houdini 20, this has manifested as a new "view-oriented" animation process aimed at making character animation more artist-friendly. Among its key features is the ability to import source video material and display it in the viewport behind the character. Users can then lock down key poses and manipulate the character rig using new Selection HUD sets to control which rig elements can be selected. The new animation tool panel allows for quick pose creation using simple sliders.
In addition to frame-by-frame animation, which has been streamlined thanks to the new bookmarking system on the playback panel and enhancements to the motion editor, users can leverage the Houdini Dynamic Motion system for automatic generation of physically plausible movements between poses. This generated movement can then be edited interactively by manipulating trajectory curves in the viewport, similar to specialized physics-based animation tools like Cascadeur.

Рабочий процесс анимации стал возможным благодаря APEX - новой системе оценки графов в Houdini. Эта система основана на KineFX - фреймворке для риггинга персонажей, ретаргетинга и редактирования движений, который был представлен компанией SideFX в Houdini 18.5. Ключевым нововведением KineFX было представление рига персонажа как редактируемой геометрии. Однако для добавления кинематики использовался язык выражений VEX из Houdini, который оказался неэффективным для создания сложных ригов.

APEX (All-Purpose EXecution graph) takes a step further, allowing the conversion of "everything [needed] for animation" into geometry, including locators, constraints, and curves. SideFX describes it as "specially designed" for real-time workflows, enhancing interactivity by deferring the evaluation of the graph until it's absolutely necessary and then compiling the graph "on the fly". APEX rigs seamlessly integrate with existing KineFX workflows, such as animation retargeting. According to the key message in Houdini 20, "APEX and KineFX work as a team: you don't have to choose between them."

Another significant change in Houdini 20 is that the Karma XPU renderer is now ready for use. This update has brought the CPU/GPU version of the renderer closer to feature parity with Karma CPU, which operates solely on CPU and became the default renderer in Houdini 19.5. Key changes include support for deep images, the ID Cryptomatte matte generation system, a broader range of light types including Physical Sky Light, geometric and IES lights. Overall, Karma has also gained many new features, such as support for the OCIO 2.0 color management standard and expanded MaterialX support.

Houdini 20 also lays the groundwork for the successor to Karma by implementing Vulkan support. Similar to Blender, this new graphics API is initially utilized for viewport rendering, replacing the outdated OpenGL. The Vulkan viewport is currently an experimental feature and is disabled by default, but on SideFX's website, there is a video showcasing its usage in the feather system of Houdini 20. However, SideFX has much larger plans for Vulkan: they describe it as the foundation for a new real-time cinematic renderer that will be "a leap above" Karma, offering both greater visual fidelity and a "magnitude" increase in performance for rendering final quality.

Environment artists in Houdini 20 have received a new volumetric cloud system with artistic control capabilities. Users can create clouds based on groups of spherical primitives and have control over their shape by generating individual primitives along splines or filling polygonal meshes. The appearance of the cloud can be adjusted by applying existing noise patterns to its base form. Additionally, for working with backgrounds, Houdini can generate clouds that fill a two-dimensional field or a three-dimensional volume, providing various noise types to control the outcomes.
Unusually for a Houdini version, while other simulation tools are not the primary focus of Houdini 20, updates to key toolsets are still present. For fluid simulation, the FLIP-based fluid system introduced in Houdini 19.5 has been complemented by a new SOP-based Whitewater system for creating foam and splashes.

For simulating small-scale scenarios, the new "Bubble Solver" generates seamless clusters of bubbles that realistically adhere to each other without intersecting. Additionally, a new ocean creation procedure generates a realistic ocean surface from low-resolution geometry at render time without the need for texture baking. It supports multiple wave spectrum types and functions with Karma and all third-party Hydra rendering delegates supported by Houdini, including Arnold, Redshift, and RenderMan.
To create fine surface ripples, there's also a new Ripple Solver. It functions similarly to the Shallow Water solver in Houdini 19.5 but employs spring-based simulation acting on the surface geometry instead of fluid simulation acting on height fields. This allows for broader usage: in one of the demonstrations, it was used to create ripples on flesh.

In the Pyro toolset for simulating gaseous fluids, new parameters have been introduced to apply gravity, with the intensity of the effect dependent on the fluid density. When simulating dust and debris, new control elements enable the acceleration of denser parts of the dust cloud during its fall, as demonstrated in the video above. Additionally, the rigid body dynamics toolset has gained support for sticky collisions and a new option for breaking curved glass, while the Vellum cloth simulation now supports wind shadows. The crowd simulation toolkit has received a new trajectory system, allowing control over the behavior of a small number of crowd agents without the need to rerun the simulation.

Among other features, there's the experimental Quad Remesh system for converting models into low-polygon meshes, while the Topo Transfer system received a new Topo Flow node. Additionally, Solaris, the layout and look development environment in Houdini, has been updated, incorporating several minor new features such as support for parallax occlusion mapping to create 3D interior spaces when rendering buildings. Beyond the main Houdini application, there's a new shelf of tools in Houdini Engine for Unreal.

Among other advancements, SideFX has embarked on developing a new generation of AI-driven tools for Houdini. During her presentation, Christine Barrie, Vice President of Product Development, noted that ultimately, this work will "touch every fiber" of the application. However, the company believes that machine learning will complement traditional procedural workflows in Houdini rather than replace them. In the core version of Houdini 20, there are only a few machine learning features. However, in the Content Library - a free online repository of add-ons for Houdini by SideFX - two new ML toolsets have emerged. Both of these utilize the ONNX Inference node, necessary for applying pre-trained ML models to source data. The ML Deformer mimics the result of Vellum cloth simulation but computes faster, while ML Terrain demonstrates how machine learning can be applied to generate terrains or landscapes.

Houdini 20 is available for Windows 8 and higher, macOS 11.0 and higher, as well as various Linux distributions. The software is offered in multiple editions. The full version, Houdini FX, is priced at $4,495 for a node-locked license and $6,995 for a floating license. The cost of Houdini Core, which lacks advanced simulation tools, is $1,995 for a node-locked license and $2,995 for a floating license. Additionally, there is a free educational version called Houdini Apprentice and a more affordable rental-only version, Houdini Indie, which save files in different formats.