fix: Start and end times have to be relative to the masterbar not absolute

src/midi/MidiTickLookup.ts

@@ -421,14 +421,15 @@ export class MidiTickLookup {
         if (currentMasterBar) {
             // pre-beat grace notes at the start of the bar we also add the beat to the previous bar
             if (start < 0 && currentMasterBar.previousMasterBar) {
-                const previousStart = currentMasterBar.previousMasterBar!.end + start;
+                const relativeMasterBarEnd = currentMasterBar.previousMasterBar!.end - currentMasterBar.previousMasterBar!.start;
+                const previousStart = relativeMasterBarEnd + start;
                 const previousEnd = previousStart + duration;
 
                 // add to previous bar 
-                currentMasterBar.previousMasterBar!.addBeat(beat, previousStart, previousStart, currentMasterBar.previousMasterBar!.end - previousStart);
+                currentMasterBar.previousMasterBar!.addBeat(beat, previousStart, previousStart, duration);
 
                 // overlap to current bar?
-                if(previousEnd > currentMasterBar.previousMasterBar!.end) {
+                if(previousEnd > relativeMasterBarEnd) {
                     // the start is negative and representing the overlap to the previous bar.
                     const overlapDuration = duration + start;
                     currentMasterBar.addBeat(beat, start, 0, overlapDuration);

test/audio/MidiTickLookup.test.ts

@@ -1,3 +1,4 @@
+import { AlphaTexImporter } from '@src/importer/AlphaTexImporter';
 import { ScoreLoader } from '@src/importer/ScoreLoader';
 import { ByteBuffer } from '@src/io/ByteBuffer';
 import { Logger } from '@src/Logger';
@@ -574,8 +575,6 @@ describe('MidiTickLookupTest', () => {
     })
 
 
-
-
     it('cursor-snapping', async () => {
         const buffer = await TestPlatform.loadFile('test-data/audio/cursor-snapping.gp');
         const settings = new Settings();
@@ -616,6 +615,38 @@ describe('MidiTickLookupTest', () => {
         expect(secondBeat!.beatLookup.duration).to.equal(960);
     });
 
+
+    it('before-beat-grace-later-bars', () => {
+        const settings = new Settings();
+        const importer = new AlphaTexImporter();
+        importer.initFromString(`\\ts 2 4 1.1.2 | 2.1.4 3.1 | 4.1{gr} 5.1{gr} 6.1.2 | 7.1.4 8.1`, settings);
+        const score = importer.readScore();
+        const lookup = buildLookup(score, settings);
+
+        // bar 2 contains the grace notes which stole duration from fret 3 beat. 
+        const bar2 = lookup.masterBars[1];
+
+        let current = bar2.firstBeat;
+        expect(current!.highlightedBeats.map(b => b.beat.notes[0].fret).join(',')).to.equal("2");
+        expect(current!.start).to.equal(0);
+        expect(current!.duration).to.equal(960);
+
+        current = current!.nextBeat;
+        expect(current!.highlightedBeats.map(b => b.beat.notes[0].fret).join(',')).to.equal("3");
+        expect(current!.start).to.equal(960);
+        expect(current!.duration).to.equal(840); // 120 ticks stolen by grace beats 
+
+        current = current!.nextBeat;
+        expect(current!.highlightedBeats.map(b => b.beat.notes[0].fret).join(',')).to.equal("4");
+        expect(current!.start).to.equal(960 + 840);
+        expect(current!.duration).to.equal(60);
+
+        current = current!.nextBeat;
+        expect(current!.highlightedBeats.map(b => b.beat.notes[0].fret).join(',')).to.equal("5");
+        expect(current!.start).to.equal(960 + 840 + 60);
+        expect(current!.duration).to.equal(60);
+    });
+
 
     function lookupTest(
         tex: string,