Dive into the intricate process of creating a AAA-grade fire torch VFX for games. This guide uncovers advanced simulation, looping, and Unreal Engine integration techniques for stunning real-time visuals.
Creating realistic fire for video games is one of the most formidable challenges in visual effects, demanding a blend of artistic vision and technical prowess. Its dynamic, non-linear behavior makes it notoriously difficult to simulate and render efficiently in real-time. Fortunately, industry professionals like Tristan, a seasoned VFX artist, are sharing their expertise to demystify these complex processes. Through his work with Visual Tech Art (VTA), Tristan has provided a comprehensive breakdown of crafting a AAA-grade fire torch, showcasing innovative techniques using a powerful trio of tools: Houdini, Embergen, and Unreal Engine.
Tristan’s tutorial, available through Visual Tech Art, offers an unparalleled look into developing a production-ready fire torch, complete with seamless looping, robust movement handling, and sophisticated material setups. He guides viewers through every step, ensuring a result that would fit perfectly into any high-budget game title. You can learn more about Tristan and his impressive portfolio on his website.
The Core of the Flame: Houdini and Embergen
The journey begins in Houdini, where the initial flame simulation can be set up using VDBs or from scratch with a pyro source. Tristan demonstrates how a simple sphere, slightly squashed and surface-scattered with points, can be initialized with ‘burn’ and ‘temperature’ attributes. The magic truly happens within the pyro solver, where specific settings like ‘Advection Reflection’ are crucial for noise. However, the artist notes that for the core flame, Embergen often yields superior results more rapidly. Embergen’s intuitive workflow allows for quick iteration and refinement of fire simulations, making it a favorite among VFX artists.
In Embergen, the creator starts from a template, modifying the ‘sourcing shape’ to create a richer flame appearance. The true innovation here lies in the custom looping strategy, moving beyond Embergen’s built-in options. Tristan introduces a groundbreaking “double frame” technique, exporting 144 frames to generate an 8×4 (32 frames) texture per channel. By using RGBA channel packing, this provides 128 frames. The remaining 16 unique frames are ingeniously used for a horizontal flip blending technique, effectively doubling the perceived frame count and drastically reducing visible repetition for a truly seamless loop.
Crafting Seamless Loops and Sprite Sheets
Back in Houdini, the simulation is meticulously prepared for looping. File handling is managed with an ‘attribute wrangle’ to assign frames to RGB and Alpha channels. For visualization, fire color mapping ranges (Kelvin values) and color gradients are directly copied from Embergen. The seamless loop calculation implements the horizontal flip blending by offsetting the 144-frame sequence and blending in the final 16 frames in a horizontally flipped state. This is achieved using ‘time shift’ and ‘transform’ nodes, with a ‘volume mix’ node handling the blend. To prevent artifacts, a ‘temperature shift’ via another ‘attribute wrangle’ remaps the linear blend curve, cleverly hiding excessive glow during transitions.
Rendering is handled by an orthographic camera and a ‘mantra’ node, dynamically sorting frames into channel-specific subfolders. These images are then processed in the ‘image comp’ network. Each channel is imported, faded at the edges to prevent seams, and adjusted for saturation and sharpness. Individual sprite sheets are then mosaiced, converted to grayscale, and finally packed into a single 2K resolution RGBA texture using ‘channel copy’ nodes.
The Halo Effect: Building the Glow Mesh
Beyond the flames, the torch features an overlaying glow mesh, or halo. The torch mesh is imported into Houdini, scaled, and the stick portion is removed. After filling any holes, it’s converted to a VDB, then back to a mesh, poly-reduced, and normals are recalculated. A crucial step for smoother world position offsets is creating blurred normals. This involves another VDB conversion, a ‘VDB smooth’ operation, and then storing the recalculated normals as vertex colors (CD). These vertex colors are remapped from -1 to 1 to 0 to 1, and alpha values are calculated based on Y-position for a fade effect. Finally, the mesh is scaled back up and exported as an FBX, ready for Unreal Engine.
Bringing it to Life in Unreal Engine
In Unreal Engine, the exported textures and mesh are integrated. For the flame emitter, the texture’s compression is set to “vector displacement” for optimal alpha handling. A custom SubUV material function is created to implement the horizontal texture flipping logic, dynamically calculating frames and determining when a flip is needed. A custom HLSL node selects the correct RGBA channel, and flame speed is dynamically linked to particle color via ‘accumulated forces’. Quality switches and feature level switches are incorporated for optimization. A black body node maps grayscale values to fire colors, while ‘flame dim velocity’ controls emissiveness, reducing glow during fast movement. Depth fade and clipping depth fade are applied, and opacity is handled without a particle state, using emitter age for fade-in and an ‘Infinite Fade Time’ module for graceful fade-out. Refraction is also applied, carefully masked by the flame’s shape.
Dynamic Positioning and Halo Material Artistry
The Niagara ribbon positioning uses two main modules: the ‘Velocity Bezier Curve System’ and the ‘Position Ribbon’ module. The former tracks velocity, applies acceleration and drag, and calculates ‘flame dim velocity’ and ‘accumulated forces’. The latter uses these parameters to construct a Bezier spline. Specific ribbon segments are pushed down to align with the halo mesh, and a camera-facing fix prevents ribbon flipping. The ribbon’s scale dynamically adjusts based on speed.
For the halo overlaying glow mesh, a GPU emitter spawns a single particle. Panning noise is achieved by transforming the ‘trail end position’ from world to local space, normalizing it, and accumulating it into a ‘halo flame offset’ vector. This offset, along with ‘flame dim velocity’ and ‘trail end position’, is passed to the material via dynamic parameters. The Halo material extracts blurred normals from vertex colors, samples 3D noise using transformed world position and offsets, and influences a Fresnel calculation. Curves are sampled from the Fresnel value to control alpha, green, and red channels, with a black body node mapping colors. Fresnel effects are tweaked and masked with the Houdini-generated alpha vertex colors, and opacity is linked to ‘flame dim velocity’. World Position Offsets (WPO) for the halo mesh involve calculating an ‘attraction point’ and creating a mask from the vector between this point and the vertex world position, which is then multiplied by noise and the Houdini alpha vertex color mask, controlling the curviness with a power function.
Accessibility and Tools Pricing
Tristan generously provides a sample project download on Gumroad, offering full access to the project files for those eager to dive in. For further engagement with Visual Tech Art, you can join their Discord community or support them on Patreon.
Accessing these powerful tools is also made flexible for artists at all levels:
- Houdini: SideFX offers a free Houdini Apprentice version for non-commercial use, perfect for learning and personal projects. Commercial licenses like Houdini Indie and Houdini FX are available for professional work.
- Embergen: JangaFX provides a free 14-day trial to explore its real-time volumetric simulation capabilities. Full licenses are available through various subscription and perpetual options.
- Unreal Engine: The engine itself is free to download and use. Epic Games applies a 5% royalty on gross revenue over $1 million per product per quarter for commercial games, making it highly accessible for developers and artists alike.
This tutorial is a testament to the intricate artistry and technical skill required for AAA game development. By breaking down such a complex effect into manageable steps, Tristan empowers artists to push their boundaries and create truly immersive visual experiences. Exploring the project files will undoubtedly provide invaluable insights into the nuances of advanced real-time effects.
If you’re eager to enhance your game development skills, explore more about Unreal Engine techniques or dive deeper into creating stunning materials and shaders. For those passionate about crafting dynamic visuals, our Unreal Engine VFX & Simulation section offers even more expert guidance.
