gp3/gp4: extract note accent flags (0x02 heavy, 0x40 normal)

[kaizenman]

Bug

GP3File.readNote never reads flag bits 0x02 (heavy accent) and 0x40 (normal accent) from the note flags byte, even though the docstring at gp3.py:870-879 documents both flags. GP4 inherits this broken read path; only GP5 reads them correctly.

The writer side is asymmetric:

• GP3File.packNoteFlags emits 0x02 but not 0x40
• GP4File.packNoteFlags overrides to add 0x40 only

Round-tripping a note with accentuatedNote=True through PGP silently drops the flag.

Reference: alphaTab

alphaTab's Gp3To5Importer.ts:1210-1217 shows the canonical read path for both flags:

public readNote(track: Track, bar: Bar, voice: Voice, beat: Beat, stringIndex: number): Note {
    const flags = ...
    if ((flags & 0x02) !== 0) {
        newNote.accentuated = AccentuationType.Heavy;     // 0x02 = heavy accent
    } else if ((flags & 0x40) !== 0) {
        newNote.accentuated = AccentuationType.Normal;    // 0x40 = normal accent
    }

Fix

• GP3File.readNote: read both flags 0x02 and 0x40 (mirroring AT)
• GP3File.packNoteFlags: write 0x40 alongside existing 0x02
• GP4File.packNoteFlags: drop the now-redundant 0x40 override (superseded by gp3)

Verification

Added testNoteAccentuationRoundtrip in tests/test_conversion.py, parametrised over GP3/GP4/GP5 fixtures. Verifies both accentuatedNote and heavyAccentuatedNote survive a write→read cycle.

Without the fix:

• Effects.gp3 fails (accentuatedNote not preserved on round-trip)
• Effects.gp4 fails (same)
• Effects.gp5 passes (already worked correctly)

With the fix: 3/3 tests pass.

All 195 existing tests continue to pass.

[Perlence]

Thanks for pointing that out! I did some research with the original software, Guitar Pro 5.2 and Guitar Pro 4.0. Here's the complete break down:

App	Format	Operation	Parameter	Result
GP4	GP3	read	0x02	No effect
GP4	GP3	write	Heavy accentuated note	N/A
GP4	GP3	read	0x40	Accentuated note
GP4	GP3	write	Accentuated note	No effect
GP4	GP4	read	0x02	No effect
GP4	GP4	write	Heavy accentuated note	N/A
GP4	GP4	read	0x40	Accentuated note
GP4	GP4	write	Accentuated note	0x40
GP4	GP5	—	—	—
GP5	GP3	read	0x02	No effect
GP5	GP3	write	Heavy accentuated note	N/A
GP5	GP3	read	0x40	Accentuated note
GP5	GP3	write	Accentuated note	N/A
GP5	GP4	read	0x02	No effect
GP5	GP4	write	Heavy accentuated note	0x40
GP5	GP4	read	0x40	Accentuated note
GP5	GP4	write	Accentuated note	0x40
GP5	GP5	read	0x02	Heavy accentuated note
GP5	GP5	write	Heavy accentuated note	0x02
GP5	GP5	read	0x40	Accentuated note
GP5	GP5	write	Accentuated note	0x40

I'll adjust the modules so that they read and write the accentuation effects in a way that mimics the original:

Format	Operation	Parameter	Result
GP3	read	0x02	No effect
GP3	write	heavyAccentuatedNote	No effect
GP3	read	0x40	accentuatedNote
GP3	write	accentuatedNote	No effect
GP4	read	0x02	No effect
GP4	write	heavyAccentuatedNote	0x40
GP4	read	0x40	accentuatedNote
GP4	write	accentuatedNote	0x40
GP5	read	0x02	heavyAccentuatedNote
GP5	write	heavyAccentuatedNote	0x02
GP5	read	0x40	accentuatedNote
GP5	write	accentuatedNote	0x40

[kaizenman]

Maybe you can also open an issue in alphaTab? They have the same problem — 0x02 read as heavy for GP3/GP4. Your testing is much stronger argument than anything from me. If you don't have time, I can open it and link your comment as the source.

[Perlence]

Please feel free to file an issue. Guitar Pro 3 doesn't support any kind of accentuated notes. Guitar Pro 4 supports regular accentuated notes 0x40. Guitar Pro 5 supports both. You might think it's inconsistent that the accentuated effect is read from a GP3 tab, but the heavy accentuated effect isn't. However, that's an original software quirk that I'm willing to keep.