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A funtro to real-time ray-tracing
- 1. A funtro to real- time ray-tracing
- 2. Goal •Give a short overview how game engines render scenes •Compare this to ray-tracing •Sneak-peak into general-purpose GPU programming and metal •Have fun
- 3. Definitions
- 6. Where to start? •No need to start from scratch •For games you can use the rendering pipeline of an engine •Our you can use graphics libraries and build your own
- 8. Return of the Obra Dinn https://gameplaying.info/one-bit-detective-return-of-the-obra-dinn-from-the-author-of-papers-please-will-be-released-next-week
- 10. Horizon Zero Dawn https://www.forbes.com/pictures/57d0856d31358e16c5895c89/new-horizon-zero-dawn-4k
- 12. Harmony between CPU and GPU • AI, Update game world, Culling, User inputs • General purpose, sequential • I/O-sensitive • should work ahead (double / triple buffering) • sync via shared memory • Processing models, lighting, shadow, textures • only one task type, parallel • branch/memory-sensitive • should not starve • sync via shared memory
- 13. Architectures aim to make the communication fast https://www.extremetech.com/gaming/164934- xbox-one-bus-bandwidths-graphics-capabilities- and-odd-soc-architecture-confirmed-by-microsoft http://www.psdevwiki.com/ps4/PS4-documents https://devstreaming-cdn.apple.com/videos/ wwdc/ 2018/607buro3d9jn66/607/607_metal_for_game_de velopers.pdf
- 14. Rasterisation Rendering pipeline • Prepare the render passApplication •Vertex Shading •Frustum Culling •Projection •Clipping Geometry processing •Project 3D scene to 2D screen, sample pixelsRasterisation •Pixel shading •Merging •Gamma correction Pixel Processing
- 15. Application On CPU Handle user input, update game world, simulate AI Load models, textures, set render states, schedule render pass https://www.gdcvault.com/play/1021926/Destiny-s-Multithreaded-Rendering
- 16. Vertex shading ON GPU PROCESS MODEL VERTICES TRANSFORM MODEL TO WORLD COORDINATES http://www.codinglabs.net/article_world_view_projection_matrix.aspx
- 17. Frustum culling ON CPU QUERY WORLD OBJECT TREE KEEP OBJECTS WITHIN THE VIEW FRUSTUM
- 18. https://kotaku.com/horizon-zero-dawn-uses-all-sorts-of-clever-tricks-to-lo-1794385026 Frustum Culling in Horizon Zero Down - Video
- 19. Rasterisation https://www.raywenderlich.com/5493-metal-rendering-pipeline-tutorial ON GPU PROJECT 3D OBJECTS ON 2D CAMERA SCREEN SAMPLE IMAGE TO CREATE PIXELS (ANTI- ALIASING NEEDED)
- 20. Pixel/Fragment shader ON GPU INTERPOLATE BETWEEN PROJECTED VERTICES (PIXELS) CALCULATE COLOR FROM TEXTURES, NORMAL VECTORS AND BRDF
- 21. http://www.adriancourreges.com/blog/2015/11/02/gta-v-graphics-study/ • G-buffer / multiple render target / deferred rendering: • color • depth • PBR attributes (roughness, shininess)
- 22. Ray-tracing
- 23. Ray-tracing •Instead of projecting triangles on the screen, simulate the image caption of the eyes •Cast rays for each pixel, trace its path, calculate shading https://en.wikipedia.org/wiki/Ray_tracing_(graphics)
- 25. Trace •
- 26. Shade • Define the color of the ray according the path it travelled • Check if light can directly impact the intersection point • Use a Bidirectional Reflectance Distribution Function to calculate the effect of global illumination on the texture of the pixel • Shoot further rays from the intersection point into the scene with a defined distribution. Repeat from the trace step. • Real-time ingredients • Limit the depth of recursion • Optimize distribution of reflection rays • Use denoising to balance less rays
- 27. Ray-trace now • Rasterization (used for model meshes and basic texture) mixed with raytracing (lighting, shadow) supported by graphic cards (RTX) https://www.unrealengine.com/en-US/blog/porsche-nvidia-and-epic-games-reveal-the-speed-of-light-for-porsche-911-speedster-concept
- 28. Metal
- 29. Putting our knowledge to use •Option to create rasterization pipelines and boost illumination calculation with triangle raytracing •configure render pipeline •implement vertex, fragment shaders •Option for General purpose GPU programming: compute shaders for ray tracing •kernel shader
- 30. Building blocks • MTLDevice: Interface to GPU • MTKView: Shows the render output • MTLCommandQueue: Render pipeline configuration and execution queue • MTLComputePipelineState: iOS representation of our kernel function and state • MTLBuffer: Memory allocation between CPU and GPU • shaders.metal: Our compiled shader code
- 31. Metal Shading Language • C++14 with restrictions • vertex/fragment/kernel shader functions • Memory • thread: allocated on thread • device: flexible, low frequency • constant: fix, high frequency • SIMD types: float4, float4x4 • Pass input output via buffers, textures
- 32. Thread and Threadgroups • Thread: Single instance of your kernel function executed on a 1D, 2D, 3D grid • Threadgroup: Collection of threads that share a common block of memory https://developer.apple.com/documentation/metal/about_threads_and_threadgroups
- 33. Example app • Only for device • Started from a Metal example • Written In Swift • Use compute shaders, GPGPU • Use the thread ID (x, y) for ray coordinates • Using Phong BRDF with spherical UV mapping
- 34. Check out!
- 35. Conclusion •Application should keep good balance between CPU and GPU •Rasterization rendering is based on multiple decades of striving for real-time performance •Ray-tracing catches-up, currently mixed with rasterization •Both can be implemented in Metal, but rasterization is more supported
- 36. Resources •Game Engine Architecture book •Real-time rendering book •Metal Documentation