1 / 17

Alias-Free Shadow Maps

Alias-Free Shadow Maps. Timo Aila Samuli Laine Helsinki University of Technology. Outline. Brief intro to shadow mapping positive/negative features what is the fundamental problem? Our solution properties, performance Future work Q&A. Shadow maps [Williams78]. Widely used Simple

daquan-burch
Download Presentation

Alias-Free Shadow Maps

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Alias-Free Shadow Maps Timo Aila Samuli Laine Helsinki University of Technology

  2. Outline • Brief intro to shadow mapping • positive/negative features • what is the fundamental problem? • Our solution • properties, performance • Future work • Q&A

  3. Shadow maps [Williams78] • Widely used • Simple • General (anything that can be rasterized) • Aliasing artifacts

  4. Aliasing: resolution issues [Sen et al. 2003]

  5. Aliasing: incorrect self-shadowing

  6. Step 1. From light source: • Compute a shadow map(z-buffer) • Dots are sampling points • depth known only at these points

  7. Step 2. From camera: • Samples vs. pixels • Project each visible sample to light source • Determine shadow term using shadow map

  8. Shadow map sampling points  Points where the depth is computed/known Points where the depth is queried

  9. Idea: why not do it right? • Project screen-space samples to image plane of light source • Rasterize blocker geometry using them as sampling points • Depth known at correct positions  • same result as shadow rays

  10. Rasterization • Q: How to rasterize using irregular sampling points? blocker

  11. Rasterization + depth test • Test if sampling point covered • we use edge functions [Pineda88] • Depth test Let’s make it practical! • hierarchical processing of sampling points • we use axis-aligned 2D BSP

  12. Properties • Resolution issues disappear • Bias term independent of scene • Semi-transparent shadow receivers • simply transform multiple samples per pixel • Semi-transparent shadow casters • can modulate the RGB color of shadows

  13. Performance (1/2) • Scalability: random triangles @ 1024x768: • transformation of samples: ~130ms • BSP construction: ~400ms • rasterization: 1K 10K 100K 1M 145ms 381ms 1568ms 8102ms

  14. Performance (2/2) • 2.9M semi-transparent shadow casting tris @ 1536x1088: 12.6s/frame • Plenty of room for optimizations

  15. Future work • GPU implementation • are HW modifications needed? • many options, probably not BSP • Soft shadows • Smoothies & Penumbra maps should work • soft shadow volumes with shadow maps? • new physically-based methods? • Applications in ray tracing?

  16. Concurrent work • Same core idea • Different implementation • Propose hardware modifications ”The Irregular Z-Buffer and its Application to Shadow Mapping”, Gregory S. Johnson, William R. Mark, and Christopher A. Burns,The University of Texas at Austin, Department of Computer Sciences.Technical Report TR-04-09, April, 2004.

  17. Thank you! • Questions? • Acknowledgements • 3DR group at Helsinki University of Tech. • Jukka Arvo, Ville Miettinen, Tim Weyrich • $$ The National Technology Agency of Finland, Bitboys, Hybrid Graphics, Nokia, Remedy Entertainment.

More Related