feat: double-click knobs to type exact values

Double-clicking a knob opens an inline text input for precise value
entry. Enter confirms, Escape cancels, blur auto-commits. Value is
clamped to the knob's min/max range. Styled to match the synth theme.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/Knob.jsx

@@ -1,4 +1,4 @@
-import React, { useRef, useCallback } from 'react';
+import React, { useRef, useCallback, useState } from 'react';
 
 const SIZE = 32;
 const RADIUS = 12;
@@ -22,6 +22,9 @@ function describeArc(cx, cy, r, startDeg, endDeg) {
 export default function Knob({ value, min, max, onChange, color = 'var(--accent)', label, unit, formatValue }) {
   const ref = useRef(null);
   const dragRef = useRef(null);
+  const inputRef = useRef(null);
+  const [editing, setEditing] = useState(false);
+  const [editText, setEditText] = useState('');
 
   const norm = Math.max(0, Math.min(1, (value - min) / (max - min)));
   const angleDeg = START_ANGLE - norm * RANGE;
@@ -40,6 +43,7 @@ export default function Knob({ value, min, max, onChange, color = 'var(--accent)
     value.toFixed(3).replace(/0+$/, '').replace(/\.$/, '');
 
   const handlePointerDown = useCallback((e) => {
+    if (editing) return;
     e.preventDefault(); e.stopPropagation();
     dragRef.current = { startY: e.clientY, startValue: value };
     const handleMove = (me) => {
@@ -47,7 +51,6 @@ export default function Knob({ value, min, max, onChange, color = 'var(--accent)
       const sensitivity = (max - min) / 200;
       let newVal = dragRef.current.startValue + dy * sensitivity;
       newVal = Math.max(min, Math.min(max, newVal));
-      // Snap to nice values for integer ranges
       if (max - min > 10 && Number.isInteger(min) && Number.isInteger(max)) {
         newVal = Math.round(newVal);
       }
@@ -60,17 +63,66 @@ export default function Knob({ value, min, max, onChange, color = 'var(--accent)
     };
     window.addEventListener('pointermove', handleMove);
     window.addEventListener('pointerup', handleUp);
-  }, [value, min, max, onChange]);
+  }, [value, min, max, onChange, editing]);
 
   const handleWheel = useCallback((e) => {
+    if (editing) return;
     e.preventDefault(); e.stopPropagation();
     const step = (max - min) / 100;
     const newVal = Math.max(min, Math.min(max, value - Math.sign(e.deltaY) * step));
     onChange(newVal);
-  }, [value, min, max, onChange]);
+  }, [value, min, max, onChange, editing]);
+
+  // Double-click: open inline text input
+  const handleDoubleClick = useCallback((e) => {
+    e.preventDefault(); e.stopPropagation();
+    setEditText(String(typeof displayVal === 'number' ? displayVal : value));
+    setEditing(true);
+    // Focus input after render
+    setTimeout(() => inputRef.current?.focus(), 0);
+  }, [value, displayVal]);
+
+  const commitEdit = useCallback(() => {
+    const parsed = parseFloat(editText);
+    if (!isNaN(parsed)) {
+      const clamped = Math.max(min, Math.min(max, parsed));
+      onChange(clamped);
+    }
+    setEditing(false);
+  }, [editText, min, max, onChange]);
+
+  const handleInputKeyDown = useCallback((e) => {
+    e.stopPropagation();
+    if (e.key === 'Enter') {
+      commitEdit();
+    } else if (e.key === 'Escape') {
+      setEditing(false);
+    }
+  }, [commitEdit]);
+
+  const handleInputBlur = useCallback(() => {
+    commitEdit();
+  }, [commitEdit]);
+
+  if (editing) {
+    return (
+      <div className="knob-container knob-editing" onWheel={(e) => e.stopPropagation()}>
+        <input
+          ref={inputRef}
+          className="knob-input"
+          type="text"
+          value={editText}
+          onChange={(e) => setEditText(e.target.value)}
+          onKeyDown={handleInputKeyDown}
+          onBlur={handleInputBlur}
+          onPointerDown={(e) => e.stopPropagation()}
+        />
+      </div>
+    );
+  }
 
   return (
-    <div className="knob-container" onWheel={handleWheel}>
+    <div className="knob-container" onWheel={handleWheel} onDoubleClick={handleDoubleClick}>
       <svg className="knob-svg" viewBox={`0 0 ${SIZE} ${SIZE}`}
         onPointerDown={handlePointerDown} ref={ref}>
         <path className="knob-track" d={trackPath} />

src/index.css

@@ -168,6 +168,15 @@ html, body, #root {
 .knob-fill { fill: none; stroke-width: 3; stroke-linecap: round; }
 .knob-dot { fill: var(--text); }
 
+.knob-editing { display: flex; align-items: center; justify-content: center; }
+.knob-input {
+  width: 48px; height: 22px; padding: 0 4px;
+  background: var(--bg); border: 1px solid var(--accent); border-radius: 3px;
+  color: var(--accent); font-size: 11px; font-family: 'JetBrains Mono', monospace;
+  text-align: center; outline: none;
+}
+.knob-input:focus { box-shadow: 0 0 6px rgba(0,229,255,0.3); }
+
 .param-value {
   font-size: 10px; color: var(--accent); font-family: 'JetBrains Mono', monospace;
   min-width: 40px; text-align: right;