1. Half-Life 2 and Source Presented by Jay Stelly

2. Tech lead decisions  Design a better structure for code development  Investments in scripting  Improve iterative creative processes  Investments in distributed computing  Investments in optimization

3. Code development  Larger group of engineers  Larger code base  Lots of dependency  System coding vs. leaf coding  Lots of new technology, new interactions

4. Code development solutions  Reduce scope of programming decisions  Dynamic linking Binary compatibility through interfaces Similar to COM in theory, lighter weight in practice Versioning system Lots of changes behind layers Build & deploy only changed components  One file leaf coding Auto-registration systems Systematic approaches to behavior, serialization, networking, hooks

5. Code development solutions  Faster compiles DLLs are smaller Reduced dependencies Use incredibuild distributed to 12 machines 4:1 - 8:1 improvement in most cases Use VMPI Many leaf coders use edit & continue Console variables

6. Example: Shaders  Graphics API isolated in a component (Shaderapi.dll) Reduced dependency on dx9 Moved from dx8 to dx9 with almost no code changes outside this layer  Materials system isolated in a component Allows mod authors to plug-in HLSL code Leaf code uses material abstraction  Lots of custom shaders needed for speed Unrolled into light/bone/state combinations Used perl scripts to automate this metaprogramming Write one, generate thousands Use VMPI to distribute compilation of shaders Incremental loading system fast iteration by a single developer

7. Investments in scripting  General scripting languages failed for us Shader language AI behavior language Animation description language (shipped)  Simple hierarchical text blocks Simple Easy to parse Extensible No conditionals, no state Tools that operate on all scripts Maps, soundscapes, materials, surfaceproperties, scenes, ragdolls, game_sounds, etc.

8. Improve iterative creative processes  Reduce scope of creative work Decrease cost of iterations Improve quality of iterations Dynamic linking Symbolic linking  Add layers of abstraction Architect around workflow  Re-examined core production processes Level design Animation Localization Audio  Allow creative people to iterate in isolation Also in parallel

9. Example: Level design  Symbolic links to audio, scenes, animations, code  Some embedded structures remain Prefabs templates  Entity I/O Visual scripting language Connect named inputs to outputs Symbolic link to code Extensible and backwards compatible Create specialized inputs & outputs as needed

10. Example: Level design (continued)  Response system Contextual symbolic links Entity I/O can trigger concept Set of contextual choices results in symbolic link Example: male/female speech Chooses an appropriate thing to say given the character and the current game context  Shaders instead of textures Symbolic link to rendering code Symbolic link to proxy code Procedurally modify shader variables Symbolic link to actual textures

11. Example: Animation  Symbolic link to animation Can also be a blended set Serialization uses symbols Named blend parameters Models share animation, can override by name  Symbolic links to bones Add new bones to specific animations & characters Share animation among models Named attachments for code & levels Named skeleton merges for models Dynamically linked

12. Example: Animation (continued)  A composite model for animation N-way blend matrix Partial skeleton animations Gestures Facial animation + procedural eye movement Lip sync IK  All are independent layers  Author characteristic gestures & postures for characters Build tons of higher-level animations out of these building blocks  Shipped ~3 hours of scenes in HL2 vs. ~10 minutes in HL1

13. Example: Scenes  Symbolic link to marks, objects, characters Independently editable in the level  Link to AI commands MoveTo, FaceTo, LookAt  Interactive with player  Link to animations, gestures, speech Change gesture timing per-instance  Animation system builds composite from all of the above

14. Example: Audio  Game_sounds.txt Simple config file for each sound effect Allows single wave or set of random waves Edit parameters (volume, attenuation, voice stealing, pitch shift, etc) per wave file  Soundscapes.txt Position-based environmental sound Also controls mixing  Soundmixers.txt Classifies sound effects into groups across entire game Named mixes of sound groups that can be linked into soundscapes  Dsp_presets.txt DSP effect parameters, parametric algorithms Automatic DSP tuning parameters

15. Example: Audio (continued)  Surfaceproperties.txt Primarily for physics properties Physically based sounds Impacts scrapes footsteps Audio reflectance properties Audio hardness/softness for modifying physically based sounds Symbolic links to actual sounds

16. Distributed computing  Half-Life used SMP/threaded systems for offline pre-processing  Source uses distributed systems instead (VMPI) Scales higher Cheaper Better long-term (keep old machines) Good for high latency jobs  Incredibuild  VMPI Radiosity, hours in Half-Life, minutes in HL2 Visibilty Shader re-compile Scales to 32 machines  Upgraded to 1Gb/s network  Use idle workstations as slaves

17. Optimization  Lots of future work  Memory bound more often than instruction bound Much easier for leaf coders to get memory bound  Otherwise fill bound, or I/O bound usually

18. Summary  Isolate creative tasks, remove dependencies  Some architecture should be based on workflow & personnel  Programming in C++, scripting with simple text configuration files  Faster, higher quality iteration through focus, isolation, dynamic linking, reduced dependency, reduced compilation steps  Can use a larger team in a more parallel fashion