circa: 2004
genre: action-adventure
publisher: Sierra
developer: Valve

engine: Source

• atmospheric/environmental effects
  • dust: impacts, lightbeams
  • lightbeams: windows (some), scanner drone lights, spotlights
  • shaking: bullet impacts, explosions
  • shards: glass, metal, wood
  • smoke: fire, shot NPC machines
  • sparks: electricity, metal impacts (bullets, crowbar, manhack blades, etc), teleporters
  • steam: some pipes
  • water: bubbles, debris, puddles, splash, spray
  • weather: fog/haze
    • clouds (moving)?
    • wind: powerlines
  • other: door handles/pushbars move, explosions, fire, gas spray, helicopter dust/spray, projectile trails, radiation mist, scanner drone swarms; see particle effects, physics, and sound
• collision detection: see physics
• lighting: dynamic, colored, vertex & lightmap; coronas, flickering; electricfied fence, eye scanner, fire, flashlight, manhacks, scanner drones, vehicles, windows
• particle effects: debris, dust, gas, mist, smoke, sparks, splash, spray, steam, swarms
• physics: Havok engine
  • gravity: player, NPCs
  • air density, bouyancy, friction, inertia, magnetism, momentum, weight
  • weight: player character breaks wood crates/beams and glass windows
  • ragdoll bodies
  • cardboard boxes break apart yet stay connected at seams
  • turnstyle turns, signs swing
  • plastic crates hold objects (bottles, cans, etc)
  • powerlines move when hit
  • power cables move around when power plugs/teleporter/TVs moved or from spark force
  • explosion force pushes/breaks objects
  • fire breaks wooden objects
  • slippery sludge/oil
  • steam pushes objects
  • paint covers most objects
• reflection: dumpsters, eyes, hazard suit gloves, floors (tile, metal), glass, most metallic surfaces, rollers, sawblades, sewer pipes, shelves (metal), toxic waste, walls (some), water (+ puddles), weapons; pixel shaders; see environmental texture mapping
• shadows: vertical angle adjustment, fading; NPCs, moving objects
• skeletal animation: yes
• texture: 16-/32-bit depth
  • filtering: bi-/trilinear
  • mapping: bump, environmental, mip, procedural
  • decals: blood/guts, bullet holes, crowbar impacts, explosion blasts, paint splats
• transparency: fire, glass, light beams, projectile trails, smoke, steam, video screens, water
• other: pixel/vertex shaders (reflections)

player character

• character: facial animation, hazard evacuation (HEV) suit, view (white: scanner drone picture snaps, red: pain)
• footsteps: concrete, dirt, gravel, metal (duct, generic, ladder), sand, tile, water, wood
• moves: crouch, jump, pickup/drop/throw, run, shoot, sprint, strafe, swim, walk
• view: 1st-person (3rd-person with cheats)
  • pan: keyboard/mouse (+ vehicles)
  • zoom: gunscope, hazard suit

level/world design

• # levels: 68 (15 chapters)
• location: canals, towns, coast, train station, prison, City 17 (Eastern European-style city), citadel
• cutscenes: yes
• level editor: Hammer?
• environmental interaction
  • break: barrels (some), benches, boats, cart, chairs, desks, drawer cabinets, flower pots, gaspumps, glass (window panes, cars), locks, machine NPCs, piers (some), shards, signs, tables, vanities, vents, walls (some), weapons (mounted)
  • explode: barrels, alien ships, enemy vehicles
  • move: barricades, bed frames, boats, bodies, broken objects, cable spools, cargo containers, cars, computer consoles, couches, crane, drawer cabinets, dressers, dumpsters, electronic equipment (oscilloscopes?), fan blades, NPC machine parts, engines, file cabinets, ladder cage, luggage carts, mattresses, metal panels, mufflers, pet transport crates (some), pods, propane canisters/tanks, radiators, railings, shelves, signs (+ letters), stair steps, tables, toolchests, train car doors, turrets, vehicle (axels, bodies, doors, mufflers), washing machines, wheelbarrows; see pickupable objects
  • open: ammo crates, doors (normal, locker, fence gates)
  • pickup: ammo/weapons, barrels, batteries, bicycles, bones, binders, boots, bottles (glass beer/wine, plastic cleaning & soda), buckets (metal, plastic), cans (food, gas, paint, recycle, soda), cardboard boxes (large, small, nail/screw), cement blocks, Chinese food boxes, clipboard, coffee mugs, computers (cases, keyboards, monitors), concrete chunks, crates (plastic, wood), doll, electronic equipment (receivers), flower pots, health (kits, vials), jars (plastic), ladel?, lamps (desk, floor), laundry machine drums, luggage, meathooks, milk cartons/jugs, newspapers, pallets, paper bags, parts cabinets, payphone handsets, picture frames, pipe weapon (NPC), pots, power plugs, rocks, sawblades, shards, skulls, statue busts, tables, tires, toilets (some), tools (pliers, wrenches), traffic cones, vanities, watermelons, wood (beams, panels, planks, platforms); see movable objects for gravity gun-pickupable objects
  • ride: airboat, buggy, cart, crane, elevator; anything moving
  • throw: pickupable objects
  • other: activate (health/HEV chargers, soda machines, teleporter), change security camera monitor video feeds, flush toilet (some), operate crane, (left/right, extend/retract arm, pickup/drop magnetic objects), plug in power plug, pull levers, spin merry-go-round & tic-tac-toe markers, tap hula doll, tilt picture frame, turn buttons/handles, TVs turn off when power plug pulled out of socket; see physics
• puzzles: physics-based (add/remove weight, add floating objects to surface something, etc)
• traps/hazards: drowning, electricity, explosions, falling (elevator, smokestack), fan blades, fire, getting burnt/cut/crushed/hit/shot, radiation, steam, toxic waste, trains

weapons: bugbait, crossbow, crowbar, explosives (grenades), guns (.357 pistol, Combine rifle, gravity, shotgun, submachinegun), rockets; anything pickupable

NPCs

• aliens (antlions, barnacles, headcrabs, ichthyosaur, stalkers, striders, synths, vortigaunts, zombies), humans, birds (crows, pigeons, seagulls), machines (gunships, helicopters, manhacks, rollers, scanners, turrets)
• AI: friendly NPCs help character and apologize when in way, object impact reaction

inventory: weapons/ammo

other

• sound: stereo, reverb, multi-channel (2, 4, 4.1, 5.1, 7.1); cuts out (+ ringing) after close explosions