GUIDE

Crowds and living NPCs in Unreal Engine 5

Lifelike crowds start from a small seed cast built by hand: six to ten base characters per species plus a modular wardrobe. Variation tools blend and randomize them within your rules into thousands of distinct people.

Mass AI simulates the crowd; nearby people are fully animated and distant ones become cheaper animated meshes. Smart Objects and State Trees give them daily lives, and AI dialogue lets side characters talk back in many languages, within limits you set.

The steps

1. Step 6: Write the living-world rules

   Which species exist, which languages are spoken, how people vary, and how big the world must be at release. These numbers become the targets the AI expansion loop builds toward.

2. Step 45: Build the seed cast for each species

   Make 6 to 10 base heads and bodies per species covering age, build and sex, plus a modular wardrobe. This is the bare minimum the variation system needs.

3. Step 46: Generate variations from the seed

   ActorMixer blends up to six characters into new faces and bodies. On top of that, randomize morphs, skin, aging, makeup, dirt and outfits within your step 6 rules.

4. Step 47: Run crowds at scale

   Mass AI simulates thousands of people. Nearby people are fully animated; distant ones become cheaper animated meshes.

5. Step 48: Give people daily lives

   Smart Objects (benches, counters, beds, workstations) and State Trees let people go to work, shop, eat and sleep on schedules.

6. Step 49: Decide who speaks which language, and how

   Keep the main story hand-written. Use AI for side characters, small talk and barks, each limited to what that character should know.

7. Step 50: Give every species a voice

   Design voices per species and region in each language. Pre-generate barks and common lines so they cost nothing at runtime. Subtitle every line.

8. Step 51: Make faces talk

   Audio-driven lip sync animates any generated line automatically.

9. Step 52: Budget the live AI

   Every generated line costs money per player. Cap response length, limit which NPCs use live AI, and use pre-generated lines everywhere else.

Common questions