Practical Volume Rendering for realtime applications
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Slides for a talk I gave in October 2013 at Chaos Group's CG2 seminar in Sofia. Brief information about the state of Volume rendering for games and details about the TransVoxel algorithm by Eric Lengyel.
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Practical Volume Rendering for realtime applications
- 2. Practical Volume rendering for realtime applications Stoyan Nikolov
- 3. VIDEO
- 4. Who am I Stoyan Nikolov stoyan@coherent-labs.com @stoyannk Co-Founder & Tech lead @ Coherent Labs Senior Graphics dev @ Masthead Studios Senior dev @ Eutelia
- 5. Overview Why use Volume rendering at all? What is Volume rendering? Types of Volume rendering techniques Practical (today) rendering techniques
- 6. Why Volume rendering • Allows us to see „inside“ an object • Medical imaging • Industry • Biology
- 7. Why Volume rendering - Games Freedom of form
- 8. Why Volume rendering - Games Destructability EverQuest Next by Sony Online Entertainment
- 9. Why Volume rendering - Games Procedural generation
- 10. Volume rendering - Input Usually discrete volume elements — voxels
- 11. Direct rendering in RT • • • • Ray-marching distance fields Gigavoxel Sparse voxel octrees (SVO) SVO for Global Illumination slisesix demo by rgba Unreal Engine 4 by Epic Games
- 12. Indirect rendering for RT • • • Create a polygon mesh GPUs are designed for polygons Other subsystems usually expect polygons
- 13. Basic algorithms Marching cubes / tetrahedra / MC 33
- 14. Realtime requirements • We want to support very large meshes • Level of Detail (LOD) required • Difficult with MC • Transvoxel designed to solve this
- 15. Transvoxel • Outline in Eric Lengyel’s PhD thesis • Designed for RT applications • Originally implemented in C4 Engine
- 16. Transvoxel overview • Based on MC Extend equivalence classes •
- 17. Basic Algorithm • • • • Subdivide grid in blocks (once) Polygonize blocks (once) Decide blocks to draw and LOD (per-frame) Draw relevant blocks (per-frame)
- 18. The LOD solution • • • Introduce “transition cells” between levels Restricted octree for rendering Identify neighbors and draw correct transitions
- 19. Transition cells
- 21. Texturing Per-voxel material Id → Texture Ids • Triplanar projection • Two sets of textures are blended for better transitions •
- 22. Parallelism • Embarrassingly parallel • Relatively easy for GPGPU • Parts can be re-computed independently
- 23. DEMO
- 24. Dual contouring • • Solves the sharp edges Works on hermite data sets VoxelFarm engine by Voxel Farm Inc.
- 25. Comparison • MC-based algorithms faster require less memory • Dual algorithms support more geometries
- 26. Potential headaches • Memory consumption • Correct implementations sometimes tricky • Texturing