RE Engine Path Tracing Deep Dive: SER, ReSTIR GI, and DLSS RR Integration in Resident Evil Requiem & PRAGMATA

Following the recent debut of PRAGMATA and Resident Evil Requiem, the first two RE Engine games to support path tracing, CAPCOM's GDC 2026 presentation titled 'Real-Time Path Tracing in RE ENGINE for Resident Evil Requiem and PRAGMATA' is well worth exploring.

The presentation is available on the NVIDIA Game Developer YouTube channel, and that's no coincidence: NVIDIA helped a great deal with the addition of path tracing to CAPCOM's engine. Indeed, the two speakers were Hitoshi Mishima from CAPCOM's RE Engine team, who covered the architectural and artistic implementation, and Calvin Shu, a NVIDIA GeForce developer technology engineer who covered the low-level GPU performance optimization for Resident Evil Requiem and PRAGMATA.

On CAPCOM's side, the implementation was handled primarily by Kenta Nakamoto and Kosuke Nabata, who completed it in approximately one and a half years. The system is tightly integrated with NVIDIA DLSS Ray Reconstruction, which handles denoising and is essential for achieving acceptable real-time performance, which effectively limits path tracing to NVIDIA GeForce RTX hardware in these two games.

The RE Engine already supported ray tracing since the previous Resident Evil game, 2021's Village, which featured ray traced global illumination, ambient occlusion, and reflections. However, it still used rasterization for direct lighting and ray tracing only for indirect lighting. Full path tracing differs in that it handles both direct and indirect lighting through a single path-tracing pipeline, resulting in more detailed shadows, sharper reflections, more stable denoising, and stricter ambient occlusion than traditional ray tracing. BVH (Bounding Volume Hierarchy) construction runs as asynchronous compute, and both ray tracing and path tracing share the same ray query and material shader infrastructure.

At this point, the presentation got quite technical. CAPCOM used a streaming RIS approach to efficiently select the most important lights. Key design choices include:

• Brightness compensation was introduced to fix darkening artifacts in spotlight-lit regions instead of standard luminance as the reservoir update weight, camera exposure and an adjustment coefficient are used.
• A simplified BSDF (Lambertian diffuse + single-lobe specular) is used during candidate generation rather than the full BSDF, to reduce ALU cost.
• IBL (Image-Based Lighting) is excluded from the candidate set in indoor settings with high-intensity IBL, because those samples are almost always occluded and cause high variance and DLSS Ray Reconstruction degradation.
• Emissive polygons are added as explicit NEE samples using Walker's Alias Method, enabling O(1) triangle sampling weighted by area and intensity on the GPU.

RE Engine defines a 3D grid (AABB) around each punctual light, with dimensions of 16×128×128 cells, each storing a light ID bitmask. Streaming RIS references this structure at each shading point to evaluate only the lights that actually contribute to that hit position, which is the single biggest performance win for punctual light sampling.

The development team then implemented the ReSTIR GI technique specifically to stabilize DLSS Ray Reconstruction quality by reducing noise in indirect lighting. The system reuses path samples across frames; current frame paths are stored per pixel, and previous frame samples are also resampled over time.

To avoid high correlation with Ray Reconstruction (which would be unfavorable), samples are drawn from slightly offset positions relative to the previous frame's pixels rather than exact matches. A key benefit in both Resident Evil Requiem and PRAGMATA was that many scenes could be lit solely with IBL, dramatically reducing noise.

A significant portion of the presentation then focused on how Capcom used the DLSS Ray Reconstruction guide buffer to resolve specific visual artifacts, such as:

• Subsurface scattering: RE Engine's SSS blur pass caused ghost artifacts in hair regions when fed into DLSS Ray Reconstruction. The fix was to encode the luminance delta before and after scattering into the guide buffer, allowing RR to account for it.
• Frosted/blurry glass: The same subsurface scattering guide buffer approach was applied to handle blur effects on glass, which caused identical artifact types.
• Raindrops and transparent decals: DLSS Ray Reconstruction's disocclusion handling made raindrops nearly invisible. The fix used the disocclusion mask in the guide buffer, with normals before/after decal application used to compute the mask selectively. The presenters said that overuse of the mask reintroduces noise, so it must be applied conservatively.
• Animated projection texture lights: Ray Reconstruction struggled with rapidly changing animated light patterns on surfaces, like wave effects on the ground. RIS animation weights were compared against overall streaming RIS weights to estimate per-shading-point contribution, and the disocclusion mask was applied proportionally.
• Holograms: Hologram patterns expressed as emissive color animations were not reflected in the DLSS Ray Reconstruction guide buffer, causing blurring. The fix replaced diffuse and specular albedo in the guide buffer with the emissive color, making the pattern visible and stable.

Both Resident Evil Requiem and PRAGMATA use CAPCOM's proprietary strand hair tech that debuted in Resident Evil 4 Remake (2023) and has been iterated on since. It uses a hybrid hardware + software rasterizer pipeline: hair clumps go through classification and culling, then hardware rasterization for opaque strands, followed by a software semi-transparency pass for the finer wisps. For ray tracing purposes, a fallback mesh substitutes for the full strand geometry in the BVH. PRAGMATA is the first game to upgrade this to a proper strand BVH, because Diana's long, flowing hair diverged too far from the proxy mesh.

Finally, NVIDIA's Calvin Shu went on stage to outline the optimization journey using a test scene from PRAGMATA with DLSS Ray Reconstruction, DLAA, and RTX 5090 at 4K resolution and default clocks. The scene featured 73 analytical lights and 32 emissive samples from a 4K array.

Stage	Frame Time	Notes
Baseline CS wavefront	21ms	13.7 avg threads/warp, 43% coherence; most time spent in punctual + emissive light sampling loops
Simplified RIS BRDF	17.7ms	15% saving; switched to world-space vanilla GGX, factored out rand calls, split UInt32 rand into two floats
Naïve SER port (no compaction)	23.5ms	Worse than baseline — expected without SER reordering enabled; 12% active threads/warp, 38% coherence
SER enabled	20.8ms	Coherence improved to 57% but instruction cache stalls dominated (35% of time waiting on instruction loads)
SER + bindless resources	~16.9ms	Static SRV references caused compiler to duplicate instructions (24K); converting to bindless dropped count back to 12K, resolved stalls
Driver optimizations	13.3ms	Not shipped at the time of the GDC 2026 talk

As you can clearly see, the path tracing optimization in RE Engine was not linear at all. There were two regression points caused by a sub-optimal implementation of Shader Execution Reordering (SER). Eventually, the key discovery in the SER investigation was that combining two separate compute shader passes (which used different static SRV bindings for direct vs. indirect light info) into a single dispatch ray call caused the compiler to duplicate instructions, doubling the instruction count to 24K and causing severe instruction cache stalls (35% of time). Converting static SRV references to bindless reduced instruction count back to 12K and resolved the bottleneck.

Closing down the presentation, Calvin Shu stressed that DXR 1.2 with Shader Execution Reordering is NVIDIA's recommendation for path traced games going forward, as it can achieve "Speed of Light" throughput (NVIDIA's term for the theoretical GPU performance ceiling) with "less plumbing". He also announced that NVIDIA will be releasing a 2.0 version of the DLSS Ray Reconstruction Disocclusion Mask, which should hopefully polish the edge cases that were encountered in the Resident Evil Requiem and PRAGMATA implementations.

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