fix: move computing spectrogram text to the center of current viewport of piano roll window

src/components/piano-roll/PianoGrid.tsx

@@ -34,6 +34,7 @@ interface PianoGridProps {
   spectrogramPower?: number;
   pianoRollZoom?: number;
   mode?: 'midi-edit' | 'spectrogram' | 'hybrid';
+  onSpectrogramLoadingChange?: (loading: boolean) => void;
 }
 
 interface CursorPosition {
@@ -62,6 +63,7 @@ const PianoGrid: React.FC<PianoGridProps> = ({
   spectrogramThresholdDb = -25,
   spectrogramPower = 0.5,
   pianoRollZoom = 1,
+  onSpectrogramLoadingChange,
 }) => {
   const [cursorPosition, setCursorPosition] = useState<CursorPosition | null>(null);
   const [isModifierPressed, setIsModifierPressed] = useState(false);
@@ -243,6 +245,7 @@ const PianoGrid: React.FC<PianoGridProps> = ({
             thresholdDb={spectrogramThresholdDb}
             power={spectrogramPower}
             zoom={pianoRollZoom}
+            onLoadingChange={onSpectrogramLoadingChange}
           />
         )}
 

src/components/piano-roll/PianoRoll.css

@@ -159,13 +159,37 @@
   color: #ff4444;
 }
 
+.piano-roll-content-outer {
+  position: relative;
+  flex: 1;
+  overflow: hidden;
+}
+
 .piano-roll-content {
   display: flex;
   flex-direction: column;
-  flex: 1;
+  height: 100%;
   overflow: auto;
 }
 
+.spectrogram-loading-overlay {
+  position: absolute;
+  inset: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  pointer-events: none;
+  z-index: 100;
+}
+
+.spectrogram-loading-label {
+  padding: 6px 10px;
+  background: rgba(0, 0, 0, 0.6);
+  color: #aaa;
+  font-size: 11px;
+  border-radius: 3px;
+}
+
 .piano-grid-header {
   display: grid;
   grid-template-columns: repeat(var(--max-number-of-bars), var(--region-grid-bar-width));

src/components/piano-roll/PianoRollContent.tsx

@@ -1,4 +1,4 @@
-import React, { useMemo, useState, useRef, useEffect } from 'react';
+import React, { useMemo, useState, useRef, useEffect, useCallback } from 'react';
 import { DEBUG_MODE } from '../../constants';
 import { KGMidiRegion } from '../../core/region/KGMidiRegion';
 import { KGMidiNote } from '../../core/midi/KGMidiNote';
@@ -60,6 +60,11 @@ const PianoRollContent: React.FC<PianoRollContentProps> = ({
   pianoRollZoom = 1,
 }) => {
   const isSpectrogram = mode === 'spectrogram';
+  const [spectrogramLoading, setSpectrogramLoading] = useState(false);
+  const handleSpectrogramLoadingChange = useCallback((loading: boolean) => {
+    setSpectrogramLoading(loading);
+  }, []);
+
   // Get KGCore instance
   const core = KGCore.instance();
 
@@ -257,38 +262,48 @@ const PianoRollContent: React.FC<PianoRollContentProps> = ({
   }, [isRecording, recordingNotes, activeRegion]);
 
   return (
-    <div
-      className="piano-roll-content"
-      ref={contentRef}
-    >
-      <PianoGridHeader maxBars={maxBars} timeSignature={timeSignature} />
+    <div className="piano-roll-content-outer">
+      <div
+        className="piano-roll-content"
+        ref={contentRef}
+      >
+        <PianoGridHeader maxBars={maxBars} timeSignature={timeSignature} />
 
-      <div className="piano-roll-body">
-        <PianoKeys activeRegion={activeRegion} />
+        <div className="piano-roll-body">
+          <PianoKeys activeRegion={activeRegion} />
 
-        <PianoGrid
-          gridRef={pianoGridRef}
-          onDoubleClick={isSpectrogram ? () => {} : handleGridDoubleClick}
-          onClick={isSpectrogram ? () => {} : handleCombinedClick}
-          onMouseDown={isSpectrogram ? () => {} : handleBackgroundMouseDown}
-          isBoxSelecting={isSpectrogram ? false : isBoxSelectingRef.current}
-          selectionBox={isSpectrogram ? { startX: 0, startY: 0, endX: 0, endY: 0 } : selectionBoxRef.current}
-          regionStartBeat={activeRegion?.getStartFromBeat() || 0}
-          selectedMode={selectedMode}
-          keySignature={keySignature}
-          chordGuide={chordGuide}
-          audioRegion={audioRegion}
-          trackId={trackId}
-          projectName={projectName}
-          bpm={bpm}
-          spectrogramThresholdDb={spectrogramThresholdDb}
-          spectrogramPower={spectrogramPower}
-          pianoRollZoom={pianoRollZoom}
-        >
-          {memoizedNotes}
-          {!isSpectrogram && recordingNoteOverlays}
-        </PianoGrid>
+          <PianoGrid
+            gridRef={pianoGridRef}
+            onDoubleClick={isSpectrogram ? () => {} : handleGridDoubleClick}
+            onClick={isSpectrogram ? () => {} : handleCombinedClick}
+            onMouseDown={isSpectrogram ? () => {} : handleBackgroundMouseDown}
+            isBoxSelecting={isSpectrogram ? false : isBoxSelectingRef.current}
+            selectionBox={isSpectrogram ? { startX: 0, startY: 0, endX: 0, endY: 0 } : selectionBoxRef.current}
+            regionStartBeat={activeRegion?.getStartFromBeat() || 0}
+            selectedMode={selectedMode}
+            keySignature={keySignature}
+            chordGuide={chordGuide}
+            audioRegion={audioRegion}
+            trackId={trackId}
+            projectName={projectName}
+            bpm={bpm}
+            spectrogramThresholdDb={spectrogramThresholdDb}
+            spectrogramPower={spectrogramPower}
+            pianoRollZoom={pianoRollZoom}
+            onSpectrogramLoadingChange={handleSpectrogramLoadingChange}
+          >
+            {memoizedNotes}
+            {!isSpectrogram && recordingNoteOverlays}
+          </PianoGrid>
+        </div>
       </div>
+      {spectrogramLoading && (
+        <div className="spectrogram-loading-overlay">
+          <div className="spectrogram-loading-label">
+            Computing spectrogram…
+          </div>
+        </div>
+      )}
     </div>
   );
 };

src/components/piano-roll/SpectrogramCanvas.tsx

@@ -13,6 +13,7 @@ interface SpectrogramCanvasProps {
   thresholdDb: number;
   power: number;
   zoom: number;
+  onLoadingChange?: (loading: boolean) => void;
 }
 
 const PITCH_BINS = 128;
@@ -55,6 +56,7 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
   thresholdDb,
   power,
   zoom,
+  onLoadingChange,
 }) => {
   const canvasRef = useRef<HTMLCanvasElement | null>(null);
   const [loading, setLoading] = useState(true);
@@ -70,6 +72,8 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
   const zoomRef = useRef(zoom);
   useEffect(() => { zoomRef.current = zoom; }, [zoom]);
 
+  useEffect(() => { onLoadingChange?.(loading); }, [loading, onLoadingChange]);
+
   const renderSpectrogram = useCallback((
     result: SpectrogramResult,
     sampleRate: number,
@@ -240,35 +244,16 @@ const SpectrogramCanvas: React.FC<SpectrogramCanvasProps> = ({
   }, [audioRegion, trackId, projectName, bpm]);
 
   return (
-    <>
-      <canvas
-        ref={canvasRef}
-        style={{
-          position: 'absolute',
-          top: 0,
-          left: 0,
-          zIndex: 0,
-          pointerEvents: 'none',
-        }}
-      />
-      {loading && (
-        <div
-          style={{
-            position: 'absolute',
-            top: 0,
-            left: 0,
-            zIndex: 1,
-            padding: '6px 10px',
-            background: 'rgba(0,0,0,0.6)',
-            color: '#aaa',
-            fontSize: '11px',
-            pointerEvents: 'none',
-          }}
-        >
-          Computing spectrogram…
-        </div>
-      )}
-    </>
+    <canvas
+      ref={canvasRef}
+      style={{
+        position: 'absolute',
+        top: 0,
+        left: 0,
+        zIndex: 0,
+        pointerEvents: 'none',
+      }}
+    />
   );
 };