The inner workings of a vr capable game engine
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A talk I gave at the Danish Technical University on 9 May 2017. It is a very high-level look at the logic in Fugl, and some details have been simplified to make it easier to communicate.
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The inner workings of a vr capable game engine
- 1. The inner workings of a VR capable game engine @gormlaigorm@kotoristudios.com
- 2. International Team ● @melodive ● @marcoapc_art ● @martinkvale ● @gormlai @gormlaigorm@kotoristudios.com
- 3. Gorm Lai ● MSc from DAIMI 2004 ● Worked on 16 commercial games ● Started in VR in 2001 at Center for Advanced Visualisation and Interaction in Aarhus ● Worked on games, interactive installations and vr since then @gormlaigorm@kotoristudios.com
- 6. Basic VR Requirements User needs to feel in control 100% of the time @gormlaigorm@kotoristudios.com
- 7. Basic VR Requirements User needs to feel in control 100% of the time ● Immediate reaction on input @gormlaigorm@kotoristudios.com
- 8. Basic VR Requirements User needs to feel in control 100% of the time ● Immediate reaction on input ● Minimize interpolation on direct movement @gormlaigorm@kotoristudios.com
- 9. Basic VR Requirements User needs to feel in control 100% of the time ● Immediate reaction on input ● Minimize interpolation on direct movement ● Movement needs to map intuitively for the brain ○ 3rd person can help @gormlaigorm@kotoristudios.com
- 10. Basic VR Requirements User needs to feel in control 100% of the time ● Immediate reaction on input ● Minimize interpolation on direct movement ● Movement needs to map intuitively for the brain ○ 3rd person can help ● 90 fps on each eye @gormlaigorm@kotoristudios.com
- 11. Possible VR Improvements ● Better ground camera ● Crashes can be dis-orientering ● Bird can move out of view ● Turns can be uncomfortable @gormlaigorm@kotoristudios.com
- 12. Key Realtime Challenges ● Terrain Generation (cpu) ● Terrain Generation (gpu) ● Populating world with animals ● Updating AI ● Sounds ● Tesselate the bird ● VR Rendering ● General performance @gormlaigorm@kotoristudios.com
- 15. Terrain ● Cylindric World ● Everything divided into slices of 1024x256x32 voxels @gormlaigorm@kotoristudios.com
- 16. Terrain ● Cylindric World ● Everything divided into slices of size 1024x256x32 ● 64 Buckets @gormlaigorm@kotoristudios.com
- 17. Terrain ● Cylindric World ● Everything divided into slices of size 1024x256x32 ● 64 Buckets ● Terrain generated ahead of player and saved as a slice @gormlaigorm@kotoristudios.com
- 18. Terrain ● Cylindric World ● Everything divided into slices of size 1024x256x32 ● 64 Buckets ● Terrain generated ahead of player and saved as a slice ● Bucket contents are loaded on demand on a separate thread @gormlaigorm@kotoristudios.com
- 19. Terrain - Typical Frame MAIN THREAD CHECK TERRAIN UPDATE COPY COMPUTE DATA COPY RENDER DATA RENDER DISPATCH COMPUTE GENERATE THREAD CHECK TERRAIN UPDATE & COMPUTE & SAVE SLICE IF NEEDED (typically takes much longer than one frame) LOAD THREAD LOAD SLICE (typically much faster than one frame) READ PLAYER POSITION @gormlaigorm@kotoristudios.com
- 24. Populating the World ● World must always seem full of life @gormlaigorm@kotoristudios.com
- 25. Populating the World ● World must always seem full of life ● Animals must spawn in plausible places ○ Crabs near the beach ○ Fish in the water ○ Eagles high up in the mountains @gormlaigorm@kotoristudios.com
- 26. Populating the World ● World must always seem full of life ● Animals must spawn in plausible places ○ Crabs near the beach ○ Fish in the water ○ Eagles high up in the mountains Main data structure for populating is a KD-Tree @gormlaigorm@kotoristudios.com
- 27. AI ● Update all animals within range @gormlaigorm@kotoristudios.com
- 28. AI ● Update all animals within range ● KD-Tree of animals balanced every frame @gormlaigorm@kotoristudios.com
- 29. AI ● Update all animals within range ● KD-Tree of animals balanced every frame ● KD-Tree used for lookup of close by animals @gormlaigorm@kotoristudios.com
- 30. AI ● Update all animals within range ● KD-Tree of animals balanced every frame ● KD-Tree used for lookup of close by animals ● State machines / Behaviour trees used for local AI @gormlaigorm@kotoristudios.com
- 31. AI - Typical Frame MAIN THREAD CHECK TERRAIN UPDATE COPY COMPUTE DATA COPY SIMULATION DATA RENDER DISPATCH COMPUTE UPDATE THREAD UPDATE WORLD SIMULATIONS AND PHYSICS (typically much faster than one frame) READ PLAYER POSITION @gormlaigorm@kotoristudios.com
- 32. General Performance 1 ● Multi threading ● Absolutely essential for performance ● Primitives: ○ std::mutex / std::recursive_mutex ○ std::condition_variable ○ std::lock_guard / std::unique_lock ○ custom thread safe containers @gormlaigorm@kotoristudios.com
- 33. General Performance 2 ● Custom task manager ● Everything that doesn’t run on the gpu or the main thread is a task ● Tasks can also run on the main thread ○ Allows tasks to reschedule themselves for ogl data. For example load thread might preprocess data, then schedule sub-task on main to hand processed data to opengl @gormlaigorm@kotoristudios.com
- 34. General Performance 3 ● Minimize dynamic allocations ● Allocate as much data as possible up front ● Object pools ● Double/triple buffering of data structures ● Avoid graphs with pointers as it causes caching issues @gormlaigorm@kotoristudios.com
- 35. General Performance 4 ● Avoid recursion @gormlaigorm@kotoristudios.com
- 36. General Performance 5 ● Custom culling algorithm ● Use chunks of size 32x32x32 ● At load time generate connectivity graph inside each chunk ○ Which 6 sides in a chunk are connected? ○ Build graph with connected chunk ● Each frame traverse from camera pos @gormlaigorm@kotoristudios.com
- 37. VR Render ● The easy part! ● For each frame: ○ Update the world ○ For each frame: ■ Calculate perspective matrix ■ Setup render target ■ Render frame ○ Submit frame to vr headset @gormlaigorm@kotoristudios.com
- 38. Open Source ● SDL ● SDL_mixer ● Cpp fsm ● Glm ● Glsl-optimiser ● Dear Imgui ● Micropather ● rapidjson ● stb libs ● misc noise libs @gormlaigorm@kotoristudios.com