Fast Indirect Illumination Using Two Virtual Spherical Gaussian Lights

This is an improved implementation of "Fast Indirect Illumination Using Two Virtual Spherical Gaussian Lights" on Microsoft MiniEngine. It roughly approximates virtual point lights (VPLs) with two virtual spherical Gaussian lights (VSGLs) for real-time single-bounce indirect illumination.

Method Overview

• Approximate diffuse-to-diffuse, diffuse-to-glossy, glossy-to-diffuse, and glossy-to-glossy reflections
• Completely dynamic, no precomputation and no lookup tables
• Specialized for scenes locally lit by a spotlight

Algorithm

1. Generate VPLs by rendering a reflective shadow map
2. Approximate the VPLs into a diffuse VSGL and glossy VSGL
3. Compute lighting from the two VSGLs

Accurate Spherical Gaussian (SG) Lighting

We use an accurate SG lighting method presented in "Hierarchical Light Sampling with Accurate Spherical Gaussian Lighting" (SIGGRAPH ASIA 2024 Conference Paper). For the GGX microfacet BRDF under sharp SG lights, this method produces higher-quality highlights than the conventional anisotropic SG lighting method [Xu et al. 2013].

|<img width="256" src="images/asg_lighting.webp">|<img width="256" src="images/reference_sg_lighting.webp">|<img width="256" src="images/ndf_filtering-based_sg_lighting.webp">| |:---:|:---:|:---:| |Anisotropic SG lighting<br>[Xu et al. 2013]|Our SG lighting<br>[Tokuyoshi et al. 2024]|Reference|

Limitations

• Light leaks
• No indirect shadows
• Lack of illumination details due to the rough approximation

Requirements

• Windows 10
• Visual Studio with Windows SDK

Getting Started

1. Open VSGL/VSGL.sln
2. Select configuration: Debug (full validation), Profile (instrumented), Release
3. Build and run

Controls

Camera

• Forward/Backward/Strafe: left thumbstick or WASD (FPS controls)
• Up/Down: triggers or E/Q
• Yaw/Pitch: right thumbstick or mouse

Light

• Forward/Backward/Strafe: left thumbstick or WASD (FPS controls) + left mouse button
• Up/Down: triggers or E/Q + left mouse button
• Yaw/Pitch: right thumbstick or mouse + left mouse button

Others

• Toggle slow movement: click left thumbstick or lshift
• Open debug menu: back button or backspace
• Navigate debug menu: dpad or arrow keys
• Toggle debug menu item: A button or return
• Adjust debug menu value: dpad left/right or left/right arrow keys