See How Stylized Rain VFX Can Be Set Up in Houdini & Octane Render

Introduction

Hey there! I'm a 3D generalist exploring methods of computer graphics for film and games. I started learning 3D a few years ago by creating educational animations and short animated films as personal projects. I've delved into the realm of 3D without any formal education in visual effects, like many artists and developers I have relied heavily on online tutorials and courses. I have a background in mathematics which has unexpectedly become a valuable asset in this creative realm. It helps me in building visual effects setups and describing motion and shapes algorithmically.

Recently, I launched a website where I share my projects, offering project breakdowns, tools, and insights into my creative process. These days, my focus revolves around Houdini and Unreal Engine, with a particular emphasis on developing tools for fellow 3D artists and game developers. Join me on this exciting journey!

Houdini

I started learning Houdini around 2 years ago. Initially, my interest was driven by curiosity to explore all major 3D packages to test the available graphics tools in the market. At that time, I didn't know much about Houdini, but it quickly became a DCC software of my choice due to its procedural nature, scalability, and ease of customization in tool building. I would say that the main challenge of learning Houdini is not exactly related to Houdini itself but to understanding the fundamental concepts of general 3D graphics. Once you are familiar with it, Houdini becomes one of the most intuitive software in my experience. 

The Stylized Rain VFX Project

I started by gathering references, with the animated movie "Garden of Words" serving as my main stylistic inspiration. The main goal and challenge was to recreate a 2D animation sequence into a 3D scene while keeping the same stylized feel of 2D. 

The creation of stylized rain VFX in Houdini involved several key steps. Firstly, I initiated a particle simulation to act as the source of rain. In Houdini, this can be done by scattering points on a plane geometry and introducing a downward velocity attribute or applying a gravity force to influence the scattered points' movement.

The second step involves generating a 3D splash geometry sequence. To emulate a 2D style, I structured a 3D effect resembling a flipbook used in 2D animation. I created multiple splash geometry files, playing them sequentially to achieve a distinctive choppy/stop-motion animated appearance. Leveraging Houdini's noise functions and procedural geometry manipulation tools, I could produce diverse versions of the splash geometry, introducing variability without the need for manual remodeling. Once the splash sequences were prepared, the final part involved copying them onto rain particles whenever they collided with the ground (water) plane.

The last step was creating a responsive water surface that produces ripples upon contact with rain particles. Fortunately, Houdini provided a great tool called the ripple solver, designed precisely for this purpose. The ripple solver takes two inputs: the rest geometry (our undeformed water plane) and the deformed geometry (water plane with points pushed downwards when colliding with rain particles). In each frame, the ripple solver adeptly displaced our water plane geometry, mimicking the propagation of ripples on a real surface.

My rendering and lighting setup follows a straightforward approach. I incorporated an HDRI for overall ambient light, complemented by a designated "toon light" interacting exclusively with geometry linked to Octane's Toon shader. Applied to the splash geometry, it introduces a distinctive stylized/cell-shaded aesthetic. Meanwhile, the rest of the scene uses standard PBR shading, together with Octane's path tracing kernel for rendering. This combination results in an interesting effect that balances realism and stylized elements.

Conclusion

For those eager to explore Houdini, there's a wealth of resources to guide you on your learning journey. If you're starting from scratch, diving into YouTube tutorials is a great way to familiarize yourself with Houdini's user interface. Taking a moment to delve into the fundamentals of general computer graphics, such as the building blocks of 3D models and shading models, provides a solid foundation applicable across various 3D software.

If you're transitioning from other 3D packages like Blender or Cinema 4D, along with YouTube tutorials, I highly recommend checking out Houdini FX Course. It's a subscription-based course website that efficiently gets you up to speed. Once you feel confident with Houdini's basic tools, I encourage you to choose a reference artwork that sparks your inspiration and attempt to recreate it. Don't hesitate to use Google whenever you get stuck. Computer graphics is a vast field, and the learning path varies based on your goals. Starting from the basics is always a wise approach. Most importantly, enjoy the process! 

Everything CG, 3D Artist / Game Developer

Interview conducted by Theodore McKenzie