Half-Life 2 and SourcePresented by Jay Stelly

Tech lead decisions

Design a better structure for code development Investments in scripting Improve iterative creative processes Investments in distributed computing Investments in optimization

Code development

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

Optimization

Lots of future workMemory bound more often than instruction bound

• Much easier for leaf coders to get memory bound

Otherwise fill bound, or I/O bound usually

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