Rasterization and Ray Tracing in Real-Time Applications (Games)

1. Rasterization and Ray Tracing in Real-Time Applications (Games) Andrew Graff

2. Overview • What are rasterization and ray tracing • Why rasterization is King • How rasterizationworks • Pros/Cons • How ray tracing works • Pros/Cons • Conclusion • Questions?

3. What is rasterization and ray tracing? • Rasterization • Given a set of rays and a primitive, efficiently compute the subset of rays hitting the primitive • Ray Tracing • Given a ray and a set of primitives, efficiently compute the subset of primitives hit by the ray

4. Why rasterization is King • Early 80’s • Development was being done on several graphical visualization techniques, but the two major were rasterization and ray tracing. • Ray tracing involved complex and time consuming calculations • Rasterization was relatively simple and required little computation time • Bottom line: Cost of hardware

5. How rasterization works

6. How rasterization works • Application • This is the application that has the information about what is to be rendered. • Sends information about vertex locations of scene to graphics hardware.

7. How rasterization works • Vertex shader • Collects information about vertices one triangle at a time • Multiple vertex shaders in parallel • Gathers X, Y, and Z information for each vertex • Also gather light information if object is directly lit by a source • Optimization: Z-culling

8. How rasterization works • Rasterizer • Converts vertex information into pixel representation

9. How rasterization works • Shader • Most difficult stage • Multiple pixel shaders in parallel • Two primary methods; shadow maps and shadow volumes • Texture filtering • Bump mapping

10. How rasterization works • Framebuffer • Memory structure that holds final information and is sampled for display • Multiple ways to sample • May or may not update all pixels (if no update)

11. Example of shadow volumes

12. Rasterization • Pros • Hardware is ubiquitous. • Hardware is inexpensive. • Primary real-time graphics method, therefore, lots of people developing new techniques and improving all the time. • Rasterization pipeline has evolved to be more flexible allowing for new techniques to be developed. • Cons • Difficult to render realistic images. • Requires new and complex algorithms to solve simple problems like shadows, light, and reflection. • Large memory requirements.

13. How ray tracing works

14. How ray tracing works • Ray-generation • Creates a ray that will travel into or through the scene • May be called by the shading stage

15. How ray tracing works • Ray-traversal • This step follows the ray through the scene until a possible intersection is detected • Scene stored in a 3D structure, as ray passes through, queries to see if primitives exist within distance of ray

16. How ray tracing works • Intersection • Calculates if the ray actually intersects a primitive • If it intersects, move on to shading; if not, go back to ray traversal

17. How ray tracing works • Shading • Most complex stage. • Gathers all data and finalizes pixel color • Calls ray-generation to create reflection/refraction rays and shadow rays • Writes to the frame buffer

18. How ray tracing works • Framebuffer • Memory structure that holds final information and is sampled for display • Multiple ways to sample • May or may not update all pixels (if no update)

19. How ray tracing works

20. Image rendered using ray tracing

21. Image rendered using ray tracing

22. Image rendered using ray tracing • This scene was rendered with a Nvidia GTX 480 using Nvidia’sOptiX ray tracing engine • 1920x1080 resolution • The GTX 480 is capable of processing 48 million rays/s. • Runs at a stunning 4.5 fps!

23. Ray Tracing • Pros • Can create extremely realistic images • Follows line-of-sight so only calculates what can be seen • Shadows can be calculated accurately at time of rendering • Cons • Time consuming • No real ray-tracing focused hardware

24. Conclusion • Ray tracing isn’t ready for real-time yet. • Potential to combine techniques for more realistic images without sacrificing a lot of performance. • More focus on hardware and algorithms could result in real-time ray tracing.

25. Questions?