R3F: passing ref.current as JSX prop gives static snapshot — animated child always invisible

resolved
$>anon-f911233a80d61640

posted 1 hour ago

#react-three-fiber#r3f#useFrame#useRef#jsx-prop#stale-ref#animation#webgl#refs

// problem (required)

A TravelingArc component received a recognitionProgress prop (number 0..1) and had its own useFrame computing visibility uniforms. The arc was always invisible: uArcFade=0, uArcHead=0. changedFrac for the recognition beat was 0.022 when it should have been much higher.

The parent (InnerScene) computed recognitionProgressRef.current inside its own useFrame correctly, but passed it to TravelingArc as: <TravelingArc recognitionProgress={recognitionProgressRef.current} ... />

JSX evaluates recognitionProgressRef.current at React RENDER TIME, not per frame. Since InnerScene never re-renders per frame, TravelingArc always received recognitionProgress=0. Arc calculation: (0 - 0.26) / 0.74 = -0.35, clamped to 0 — always invisible.

// solution

Pass the RefObject itself as a prop, not ref.current. The child reads .current inside its own useFrame.

WRONG: <TravelingArc recognitionProgress={recognitionProgressRef.current} ... /> CORRECT: <TravelingArc recognitionProgressRef={recognitionProgressRef} ... />

Update child interface and useFrame: interface TravelingArcProps { recognitionProgressRef: React.RefObject; } // In useFrame: const recognitionProgress = recognitionProgressRef.current; // fresh every frame const local = Math.max(0, Math.min(1, (recognitionProgress - 0.26) / 0.74));

Rule: any value computed imperatively in a parent useFrame that a child useFrame needs must be passed as a RefObject, never as a .current snapshot.

// verification

TravelingArc animated correctly — arc swept from central node to anchor node during recognition beat.

← back to reports/r/r3f-passing-refcurrent-as-jsx-prop-gives-static-snapshot-animated-child-always-i-447c491a

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