Hybrid Ray Tracing

Hybrid Ray Tracing

SparkEngine's hybrid ray tracing system provides Lumen-style multi-tier global illumination, reflections, and soft shadows across all hardware tiers — from GTX 1070 Ti to RTX 4090.

Architecture

HybridRTManager (coordinator)
  ├── SDFSceneManager     (software SDFGI sphere tracing — CS 5.0+; not reachable on the Windows D3D11 path)
  ├── DXRManager          (hardware DXR 1.1 — DX12 Ultimate)
  ├── RTCompositor        (blends screen-space + RT results)
  └── ProbeSystem         (irradiance probe grid for cached GI)

Backend Selection (automatic)

GPU	Backend	Method
RTX 20xx+ (DX12)	HardwareDXR	DXR 1.1 DispatchRays, TLAS/BLAS
RDNA2+ (Vulkan)	HardwareVKRT	VK_KHR_ray_tracing_pipeline
GTX 10xx / DX11	none on Windows	HybridRTManager is only constructed behind an RHI bridge, and the Windows D3D11 path has no RHI bridge (GraphicsEngine::GetRHIBridge() is nullptr on Windows), so no hybrid RT -- including Software_SDFGI -- runs on the D3D11 path regardless of the SPARK_HYBRID_RT default. The software SDFGI backend is reachable only on the Linux RHI path.
Integrated	Disabled	Screen-space effects only

Quality Presets

Preset	Resolution	Max Steps	Bounces	Probes	Denoising
Low	25%	32	1	No	No
Medium	50%	64	2	Yes	No
High	100%	96	2	Yes	Yes
Ultra	100%	128	3	Yes	Yes

Console Commands

Command	Description
rt.status	Display current RT backend, quality, and statistics
rt.quality <off|low|medium|high|ultra>	Set quality preset
rt.mode <auto|sdfgi|hardware|off>	Override RT backend
rt.reflections <0|1>	Toggle RT reflections
rt.gi <0|1>	Toggle RT global illumination
rt.shadows <0|1>	Toggle RT soft shadows

SDFGI Software Path

The software fallback represents the scene as SDF primitives (spheres, boxes, capsules) approximating mesh bounding volumes. A compute shader sphere-traces through this representation for:

• Reflections: Trace reflected rays from GBuffer surfaces
• Global Illumination: Cosine-weighted hemisphere sampling for indirect light
• Soft Shadows: Sphere trace toward light with penumbra estimation

Performance (Software SDFGI)

GPU	Low	Medium	High
GTX 1070 Ti	~2ms	~5ms	~12ms
RTX 3060	~1ms	~3ms	~6ms

Build Configuration

# Enable hybrid RT (default ON)
cmake -B build -DENABLE_HYBRID_RT=ON

# Enable hardware DXR path (requires DX12)
cmake -B build -DENABLE_HYBRID_RT=ON -DENABLE_DXR=ON

File Structure

SparkEngine/Source/Graphics/HybridRT/
  ├── HybridRTTypes.h       — Shared types (SDFPrimitive, trace params)
  ├── HybridRTManager.h/cpp — Central coordinator
  ├── SDFSceneManager.h/cpp — SDF scene & compute dispatch
  ├── RTCompositor.h/cpp    — SS + RT result compositing
  └── ProbeSystem.h/cpp     — Irradiance probe grid

Shaders/HLSL/RayTracing/
  ├── SDFCommon.hlsl        — SDF distance functions
  ├── SDFTrace.hlsl         — SDFGI sphere tracing (CS 5.0)
  ├── SDFGenerate.hlsl      — Mesh-to-SDF generation
  ├── RTComposite.hlsl      — Result compositing
  ├── ProbeUpdate.hlsl      — Probe SH coefficient update
  ├── ProbeInterpolate.hlsl — Probe grid interpolation
  ├── DXRReflections.hlsl   — DXR reflection ray gen/hit/miss
  ├── DXRShadows.hlsl       — DXR soft shadow rays
  └── DXRAO.hlsl            — DXR ambient occlusion