PIKA

Overview

PIKA is a Vulkan-based renderer designed for mobile ray tracing and DDGI-based global illumination.

The renderer was developed to support ray tracing and global illumination in performance-constrained mobile environments. It provides multiple rendering paths so that different implementations can be evaluated and compared under the same framework.

The ray tracing implementation is divided into two API-level approaches:

Type	Description
Ray Tracing	Uses Vulkan ray tracing pipeline-based execution.
Ray Query	Uses inline ray queries inside shader stages.

The renderer is also divided into two rendering architecture categories:

Type	Description
Hybrid Ray Tracer	Performs deferred rasterization first, then applies ray tracing or ray query for selected effects.
Full Ray Tracer	Uses ray tracing or ray query as the primary rendering method.

In terms of lighting features, the ray tracers are further classified into:

Type	Description
Whitted-style Ray Tracer	Supports basic ray tracing effects such as reflection, refraction, and shadow.
DDGI Ray Tracer	Supports probe-based dynamic diffuse global illumination using DDGI.

Each renderer can be switched in real time through the UI. The project runs on devices that support Vulkan ray tracing or ray query extensions, as well as devices that do not support these extensions. On devices without ray tracing or ray query support, only the deferred rasterization renderer is available.

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Renderers

PIKA provides the following rendering modes:

Renderer	Rendering Architecture	Ray API	Global Illumination
Deferred Rasterization Renderer	Deferred rasterization	None	None
Full Ray Tracing (FRT)	Full ray tracer	Ray tracing pipeline	None
Full Ray Query (FRQ)	Full ray tracer	Ray query	None
Full Ray Tracing DDGI	Full ray tracer	Ray tracing pipeline	DDGI
Full Ray Query DDGI	Full ray tracer	Ray query	DDGI
Hybrid Ray Tracing (HRT)	Hybrid ray tracer	Ray tracing pipeline	None
Hybrid Ray Query (HRQ)	Hybrid ray tracer	Ray query	None
Hybrid Ray Tracing DDGI	Hybrid ray tracer	Ray tracing pipeline	DDGI
Hybrid Ray Query DDGI	Hybrid ray tracer	Ray query	DDGI
Path Tracer	Path tracing	Ray tracing pipeline	Path-traced global illumination

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Features

• Vulkan-based rendering framework
• Mobile-oriented ray tracing renderer
• Vulkan ray tracing pipeline support
• Vulkan ray query support
• Deferred rasterization renderer
• Hybrid ray tracing and ray query renderers
• Full ray tracing and ray query renderers
• DDGI-based dynamic diffuse global illumination
• Whitted-style reflection, refraction, and shadow
• Path tracing renderer
• Runtime renderer switching through UI toggles
• Fallback deferred rasterization path for devices without ray tracing or ray query support

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Technical Documentation

Additional technical details and evaluation results are provided in the docs directory.

Document	Description
Mobile-DDGI	Describes the Mobile-DDGI algorithm, including adaptive probe update, probe importance metric, probe state machine, and rendering pipeline.
Results	Summarizes rendering results, performance measurements, and comparisons across supported rendering modes.

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Assets

This project uses custom glTF assets prepared for research purposes.

The asset directory should follow a structure similar to the one used in Sascha Willems' Vulkan Assets repository.

Expected asset directory structure:

assets
├── renderer_config.ini
├── models
├── textures
├── Roboto-Medium.ttf
└── Roboto-Medium-license.txt

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Renderer Configuration

The renderer is configured through renderer_config.ini.

Example:

[AppContext]
width=2560
height=1440
overlay=1
validation=0
vsync=0
fullscreen=0
compile_shaders=1

[Asset]
# config_path=models/cornellbox/CornellBox.json

AppContext

Field	Description
width	Initial window width.
height	Initial window height.
overlay	Enables or disables the UI overlay.
validation	Enables or disables Vulkan validation layers.
vsync	Enables or disables vertical synchronization.
fullscreen	Enables or disables fullscreen mode.
compile_shaders	Enables or disables shader compilation at startup.

Asset

Field	Description
config_path	Path to the scene configuration JSON file used for loading a glTF asset.

For detailed instructions on model placement, scene configuration JSON files, texture paths, and required asset files, see:

assets/README.md

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Camera Interface

Keyboard Controls

Input	Action
W	Move forward
S	Move backward
A	Move left
D	Move right
E	Move up
Q	Move down
R	Reset to the original camera position and rotation

Mouse Controls

Input	Action
Left mouse button	Rotate camera using pitch and yaw
Right mouse button	Roll camera
Middle mouse button	Move camera along the X and Y axes
Mouse wheel	Move camera forward or backward

Arrow Key Controls

Input	Action
→	Increase yaw
←	Decrease yaw
↓	Decrease pitch
↑	Increase pitch

Camera Speed Controls

Input	Target	Action
-	Keyboard movement speed: W, A, S, D, E, Q	Decrease speed
+	Keyboard movement speed: W, A, S, D, E, Q	Increase speed
{	Mouse control speed: left, middle, and right mouse buttons	Decrease speed
}	Mouse control speed: left, middle, and right mouse buttons	Increase speed

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Related Papers

1. Taekgeun You.
   "Development and Performance Profiling of a Mobile Ray Tracing System Supporting Global Illumination."
   Master's thesis, Graduate School of Sogang University, Seoul, Korea, 2026.

2. T. You, W. Seo, D. Han, and I. Ihm.
   "Mobile-DDGI: Lightweight Probe-Based Global Illumination via Adaptive Budget Allocation."
   2026 ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games, I3D '26 Posters, San Francisco, U.S.A., May 2026.
   Paper Poster

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References

1. Sascha Willems' Vulkan Repository
   This project is based on Sascha Willems' Vulkan project structure and examples.

2. Sascha Willems' Vulkan Assets Repository
   Used as a reference for the expected asset directory structure.

3. NVIDIA RTXGI-DDGI
   Reference implementation and documentation for RTXGI and DDGI.

4. Dynamic Diffuse Global Illumination with Ray-Traced Irradiance Fields
   JCGT 2019 paper introducing DDGI with ray-traced irradiance fields.

5. Scaling Probe-Based Real-Time Dynamic Global Illumination for Production
   JCGT 2021 paper on scaling DDGI-style probe-based global illumination for production use.

6. Ray Tracing the World of Assassin's Creed Shadows
   Ubisoft presentation on ray tracing and global illumination in Assassin's Creed Shadows.

7. Adaptive Dynamic Global Illumination
   Project page for ADGI, an adaptive extension of probe-based dynamic global illumination.

8. Adaptive Dynamic Global Illumination Paper
   Paper describing adaptive resource allocation for dynamic global illumination.

9. MicroWerner's VkRadixSort
   Vulkan-based radix sort implementation used as a reference for GPU sorting.

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License

This project is not distributed under the MIT License as a whole.

PIKA contains original work by Taekgeun You and may also include or reference third-party components, algorithms, assets, and code governed by their own licenses. In particular, this project is based on Sascha Willems' Vulkan project structure and examples, which are distributed under the MIT License. DDGI-related references and implementations may be governed by different license terms, including NVIDIA RTXGI/DDGI-related licenses.

Third-party components remain under their original licenses.

See the LICENSE file for the full license terms and third-party license notices.