Fifteen common game developer interview questions
- Describe a game loop. What is delta time, and why does it matter?
- Fixed versus variable time step — trade-offs?
- What is an entity-component-system architecture?
- How do you use the dot and cross products in games?
- How would you detect collisions between many objects efficiently?
- What causes frame rate drops, and how do you profile them?
- How do you avoid garbage collection spikes in Unity or C#?
- What is object pooling?
- Explain the rendering pipeline at a high level.
- What are draw calls, and how do you reduce them?
- How does client-side prediction work in multiplayer games?
- Authoritative server versus peer-to-peer?
- How would you implement a simple state machine for enemy AI?
- What is A* pathfinding?
- Walk me through a game or prototype you built.
Loops, time and architecture
- Game loop: process input, update simulation, render, repeat. Multiply movement by delta time so speed doesn't depend on frame rate.
- Fixed time step: physics stepped at a fixed rate is deterministic and stable; rendering interpolates between steps to stay smooth.
- ECS: entities are IDs, components are plain data, systems process all entities with certain components — cache-friendly and flexible compared with deep inheritance hierarchies.
- State machines: idle, patrol, chase, attack — with transitions on conditions — remain the backbone of most game AI, with behaviour trees for more complex behaviour.
Maths and physics
| Tool | Typical use |
|---|---|
| Dot product | Is the target in front of me? Angle between vectors, lighting |
| Cross product | Surface normals, which side a point is on, torque |
| Normalisation | Direction without magnitude, for movement and aiming |
| Lerp / slerp | Smooth movement and rotation between values |
| Quaternions | Rotations without gimbal lock, smooth interpolation |
| Spatial partitioning | Grids, quadtrees, octrees or BVHs to avoid checking every pair |
Collision detection usually has a broad phase that finds candidate pairs cheaply with spatial partitioning or bounding volumes, and a narrow phase that tests those pairs precisely. Mentioning both phases is the key insight interviewers want.
Performance and memory
Frame budget is the frame: 16.7 ms at 60 frames per second, 8.3 ms at 120. Profile before optimising — CPU-bound and GPU-bound problems have different fixes. Reduce draw calls with batching, instancing and texture atlases; use level of detail and culling; pool frequently created objects to avoid allocation and garbage collection spikes in managed engines; and keep data contiguous for cache efficiency. Console and mobile roles add strict memory budgets.
Networking
Competitive games typically use an authoritative server so clients can't tamper with game state, with client-side prediction so the player's own actions feel instant, server reconciliation to correct mispredictions, and interpolation of other players' positions. Lag compensation rewinds the server's view to judge hits fairly. UDP is common because late data is useless, with reliability added selectively.
Portfolio and design discussion
Studios care deeply about shipped or playable work. Be ready to explain a system you built, a performance problem you solved, and a design decision you changed after playtesting. Gameplay roles may ask how you'd tune a jump to feel good or balance an enemy; answer with iteration and player feedback rather than a single number. See C++ interview questions and C# interview questions.
Practising
Reading answers is not the same as saying them. Pick ten of the questions above and answer them aloud against a timer; a free AI interview assistant like CoPilot Interview can ask game programming questions in a mock interview and flag answers that ran long or lacked an example. Rehearse a five-minute walkthrough of your best project, including one thing you would redo.
Disclosure: CoPilot Interview is our product, so weigh what we say about it accordingly. Everything else on this page applies whichever tool you use, or none.
Frequently asked questions
What questions are asked in a game developer interview?
Game loops and delta time, engine architecture such as ECS, vector maths, collision detection, rendering basics and draw calls, performance and memory, networking for multiplayer, simple AI and a portfolio discussion.
What is delta time in games?
The time elapsed since the last frame. Multiplying movement and animation by it keeps speed consistent regardless of frame rate.
How do games detect collisions efficiently?
With a broad phase that uses spatial partitioning or bounding volumes to find candidate pairs cheaply, then a narrow phase that tests only those pairs precisely.
Do game studios care about portfolios?
Yes, a great deal. A playable project or shipped title you can discuss in depth often carries as much weight as the technical interview.
Practise on real interview questions
Run 145 real interview questions across 10 tracks, answer out loud and see a structured answer to compare with yours. Free, no signup.
Try a practice question