feat: added an option to let user choose the vertical resolution of the spectrogram, also fixed a bug that peak of pitch in the spectrogram has been mapped to the start of the note bin instead of the center

src/util/spectrogramUtil.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, it } from 'vitest';
+import {
+  getSpectrogramPitchBinCount,
+  getSpectrogramVisibleBinRange,
+  mapMidiPitchToSpectrogramPosition,
+  normalizeSpectrogramHeightResolution,
+} from './spectrogramUtil';
+
+describe('spectrogramUtil', () => {
+  it('normalizes unsupported resolutions to the default 3x', () => {
+    expect(normalizeSpectrogramHeightResolution(1)).toBe(1);
+    expect(normalizeSpectrogramHeightResolution(3)).toBe(3);
+    expect(normalizeSpectrogramHeightResolution(5)).toBe(5);
+    expect(normalizeSpectrogramHeightResolution(2)).toBe(3);
+    expect(normalizeSpectrogramHeightResolution(undefined)).toBe(3);
+  });
+
+  it('derives pitch bin counts from the full MIDI range', () => {
+    expect(getSpectrogramPitchBinCount(1)).toBe(128);
+    expect(getSpectrogramPitchBinCount(3)).toBe(384);
+    expect(getSpectrogramPitchBinCount(5)).toBe(640);
+  });
+
+  it('maps MIDI pitches into full-range spectrogram positions', () => {
+    expect(mapMidiPitchToSpectrogramPosition(0, 1)).toBe(0);
+    expect(mapMidiPitchToSpectrogramPosition(12.5, 3)).toBe(38.5);
+    expect(mapMidiPitchToSpectrogramPosition(127, 5)).toBe(637);
+    expect(mapMidiPitchToSpectrogramPosition(-1, 3)).toBeNull();
+    expect(mapMidiPitchToSpectrogramPosition(128, 3)).toBeNull();
+  });
+
+  it('derives the visible C0-B7 subrange inside the full-resolution buffer', () => {
+    expect(getSpectrogramVisibleBinRange(1)).toEqual({ start: 12, end: 108 });
+    expect(getSpectrogramVisibleBinRange(3)).toEqual({ start: 36, end: 324 });
+  });
+});

src/util/spectrogramUtil.ts

@@ -0,0 +1,50 @@
+export const SPECTROGRAM_FULL_MIN_MIDI_PITCH = 0;
+export const SPECTROGRAM_FULL_MAX_MIDI_PITCH = 127;
+export const SPECTROGRAM_MIN_MIDI_PITCH = 12; // C0
+export const SPECTROGRAM_MAX_MIDI_PITCH = 107; // B7
+export const SPECTROGRAM_FULL_SEMITONES =
+  SPECTROGRAM_FULL_MAX_MIDI_PITCH - SPECTROGRAM_FULL_MIN_MIDI_PITCH + 1;
+export const SPECTROGRAM_VISIBLE_SEMITONES =
+  SPECTROGRAM_MAX_MIDI_PITCH - SPECTROGRAM_MIN_MIDI_PITCH + 1;
+
+export type SpectrogramHeightResolution = 1 | 3 | 5;
+
+export const SPECTROGRAM_HEIGHT_RESOLUTION_OPTIONS: SpectrogramHeightResolution[] = [1, 3, 5];
+
+export function normalizeSpectrogramHeightResolution(value: unknown): SpectrogramHeightResolution {
+  if (value === 1 || value === 3 || value === 5) {
+    return value;
+  }
+  return 3;
+}
+
+export function getSpectrogramPitchBinCount(
+  resolution: SpectrogramHeightResolution,
+): number {
+  return SPECTROGRAM_FULL_SEMITONES * resolution;
+}
+
+export function getSpectrogramVisibleBinRange(
+  resolution: SpectrogramHeightResolution,
+): { start: number; end: number } {
+  return {
+    start: (SPECTROGRAM_MIN_MIDI_PITCH - SPECTROGRAM_FULL_MIN_MIDI_PITCH) * resolution,
+    end: (SPECTROGRAM_MAX_MIDI_PITCH - SPECTROGRAM_FULL_MIN_MIDI_PITCH + 1) * resolution,
+  };
+}
+
+export function mapMidiPitchToSpectrogramPosition(
+  midiPitch: number,
+  resolution: SpectrogramHeightResolution,
+): number | null {
+  const pitchOffset = midiPitch - SPECTROGRAM_FULL_MIN_MIDI_PITCH;
+  if (pitchOffset < 0 || pitchOffset > SPECTROGRAM_FULL_MAX_MIDI_PITCH) {
+    return null;
+  }
+
+  // Anchor each MIDI pitch to the center of its semitone band so the
+  // rendered ridge lines up with the piano-roll key row rather than a boundary.
+  const scaled = pitchOffset * resolution + (resolution - 1) / 2;
+  const maxBin = getSpectrogramPitchBinCount(resolution) - 1;
+  return Math.max(0, Math.min(maxBin, scaled));
+}