ui-useframe_skill

Overview

This skill shows how to sync DOM-based UI elements with the React Three Fiber render loop using R3F v10's external useFrame. It demonstrates updating HUDs, debug overlays, and other HTML UI outside the Canvas while keeping them in perfect frame alignment with the 3D scene. The approach avoids embedding UI in the 3D scene and focuses on performance and simplicity.

How this skill works

useFrame can be called outside the <Canvas> in R3F v10+, allowing you to run a callback on every render tick. By holding a ref to a DOM element and mutating it directly inside useFrame, you update the UI in sync with the scene. You can throttle updates using the { fps: N } option to reduce DOM work and improve frame stability.

When to use it

• You need a screen-space HUD (e.g., crosshair, health bar) that stays outside the Canvas DOM tree.
• Display frequently updated debug info or telemetry synchronized with the scene.
• Avoid embedding 2D UI into 3D space but still require frame-accurate updates.
• You want lower-latency updates than React state renders can provide for high-frequency values.
• Implement simple overlays without adding Drei's Html or portals into the Canvas.

Best practices

• Use refs and direct DOM mutation instead of React state for high-frequency updates to avoid re-renders.
• Throttle expensive DOM updates with the { fps: N } option on useFrame to balance smoothness and CPU cost.
• Keep DOM mutations minimal: update textContent, transform styles, or CSS variables rather than rebuilding elements.
• Clean up any listeners or side effects when components unmount to avoid memory leaks.
• Measure performance and choose a sensible fps value (e.g., 10–30) depending on the UI importance.

Example use cases

• A fixed-position debug panel that shows camera position, FPS, and active object IDs updated every frame.
• A race-game HUD showing speed, lap time, and position synced to the render loop but rendered as normal HTML for easy styling.
• Crosshair and target lock indicators updated from raycast results each frame without adding 3D UI elements.
• Simple score or combo counters that update in near-real-time while avoiding React re-renders for every tick.