Frustum-Traced Irregular Z-Buffers: Fast, Sub-pixel Accurate Hard Shadows

Area of Science:

• Computer Graphics
• Real-time Rendering
• Shadow Computation

Background:

• Irregular z-buffers (IZBs) offer potential for high-quality shadow rendering.
• Prior IZB shadow algorithms often rely on GPU compute, limiting flexibility.
• Interactive, high-resolution shadow rendering remains a challenge in real-time graphics.

Purpose of the Study:

• To analyze and optimize a real-time antialiased hard shadow rendering system using IZBs.
• To identify and address performance bottlenecks in IZB shadow generation.
• To enable dynamic, precomputation-free shadow rendering at high resolutions.

Main Methods:

• Leveraging the standard rasterization pipeline with hardware conservative raster and early-z culling.
• Analyzing algorithmic complexity to identify performance bottlenecks.
• Exploiting the duality between IZB performance and shadow map aliasing.

Main Results:

• Achieved interactive performance at resolutions 1920x1080 and above for game and CAD assets.
• Rendered 32 samples per pixel hard shadows at approximately double the cost of single-sample shadows.
• Enabled smooth animation of sub-pixel shadows without spatial or temporal aliasing.
• Rebuilt data structures in under 1 ms per frame, comparable to ray tracers.

Conclusions:

• The enhanced IZB system provides a robust solution for high-quality, dynamic hard shadows in real-time.
• Utilizing the rasterization pipeline offers performance advantages over compute-heavy approaches.
• The system imposes no constraints on light, camera, or geometry, allowing for fully dynamic scenes.