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 });
+  });
+});