Nanite is a virtualized geometry techonlogy based on dynamic Level of Detail(LOD), introduced in Unreal Engine 5. Danite analyzes Nanite's architecture and implements a similar system using Vulkan, leveraging mesh shading techniques.
- GPU Driven Rendering
- BVH Cluster Culling
- Hi-Z Buffer
- Frustum & Occlusion Culling
- Vulkan(EXT_mesh_shader), GLFW
- C++ 20
- tiny_obj_loader
- meshoptimizer
- METIS
- ImGUI
- NVIDIA Nsight Graphics
In Danite, the CPU performs preprocessing on the input 3D model, The GPU then renders the scene based on the preprocessed data.
The 3D model is divided into meshlets, During this process, I referred this guide and make all meshlets less then 124 triangles. this guide and ensured that each meshlet contains no more than 124 triangles.
Then, I used METIS to group adjacent meshlets and performed simplification to generate higher level nodes for LOD.
Based on the generated nodes, I built a Bounding Volume Hierarchy(BVH) for culling and LOD selection. Both meshoptimizer and METIS were used in this step.
Below is a comparison between different LOD levels.
The renderer first draws the preprocessed model. For each cluster, it performs culling and calculates the appropriate LOD level. During the culling step, the Hi-Z buffer from the previous frame is used to perform occlusion culling. This entire pipeline is GPU Driven so fully executed on the GPU.
After rendering, a new Hi-Z buffer is generated using a compute shader, which will be used in the next frame for culling.
- Test environment : CPU : Intel i5-12400F, GPU : RTX 3080
- Occasionally, distant meshlets appear to flicker. This issue is suspected to be caused by floating point precision error or lack of synchronization, but it has not been resolved yet.
- Two-pass occlusion culling is not implemented. Additional optimization is expected by incorporating a second occusion pass.
- Mesh compression and streaming are not considered. The system is currently focused on handling large-scale triangle rendering, so these features are omitted.