Where is the wheel? World = parent × local
The questions 3D frontend interviews ask, with model answers built on what you measured in this course: the render loop, draw calls, matrices, normals, colour space, disposal, R3F re-renders, and WebGPU against WebGL. Each answer gives the mechanism, a number, an edge case and a trade-off.
Change the code and press Run (Ctrl+Enter). Predict what will happen first, then break it on purpose and read what changes. Your edits are saved and match the lesson page.
Ready for more? This phase has 4 hands-on exercises with automatic checks.
Practice questions
Write the code in the editor, run it, then open the model answer to compare.
Answer in two minutes, out loud: "What does dispose() free, and what doesn't it?"
Answer: "Your model looks right on desktop but too bright and flat on phones. Where do you look?"
Explain it without notes
Walk through what happens inside renderer.render(scene, camera) for one frame.
Why is a lit scene completely black, and how do you find out which cause it is?
What is the difference between WebGL 2 and WebGPU for a three.js app today?
How do you stop an R3F scene from re-rendering React 60 times a second?
Console
Nothing logged yet.Expected console output
wheel local position: 0.58, 0.35, 0
wheel world position: 2, 0.35, -0.58
by hand (bike.matrixWorld × local): 2, 0.35, -0.58
forgetting the rotation: 2.58, 0.35, 0
after moving: wheel.matrixWorld says x = 2 | getWorldPosition says x = 5