[OpenTaikoChart] "offset": (negative) should not behave similar to "offset": (positive)

[IepIweidieng]

Version

• Koioto Ver.1.0
• OpenTaikoChart Ver.3.0 (Supported Rev.: 2.4)

Current Behavior

In Open Taiko Chart Information file, both "offset": x and "offset": -x make the first measure abs(x) seconds later than when the audio starts.
For example, both "offset": 2.416 and "offset": -2.416 makes the first measure 2.416 seconds later than when the audio starts.

movieoffset has the expected behavior.

Expected Behavior

"offset": x and "offset": -x should offset the first measure in the opposite direction.

If I interpret the documentation correctly, the equation should be offset = time-point-of-chart-start − time-point-of-audio-beginning.
For example, "offset": 2.416 should make the first measure 2.416 seconds later than when the audio starts, and "offset": -2.416 should make the first measure 2.416 seconds earlier than when the audio starts.

This means that Open Taiko Chart Information offset takes the opposite sign of TJA OFFSET:
For example, "offset": 2.416 in Open Taiko Chart Information would be equivalent to OFFSET:-2.416 in TJA.

See https://github.com/IepIweidieng/TJAPlayer3/blob/gh-pages/tja.md#offset

Test Cases

Metal-Pipe.zip

Edit Metal-Pipe.tci to change offset and movieoffset.

Koioto.offset.and.movieoffset.test.mp4

Possible Solutions

See https://github.com/Koioto/OpenTaikoChart/blob/b6855a3dc635462584344cadb34f0fd1f3f3ff4c/CourseParser.cs#L45-L68.

After these lines, nowTime will be the time of the first measure, and nowTime - bgmStartChip.Time == offset should be true. However, the fails to be true for the case offset < 0.

It might be possible to solve by changing line 52

Time = nowTime - (long)(Math.Abs(offset) * 1000.0 * 1000.0),

into

Time = nowTime + (long)(Math.Abs(offset) * 1000.0 * 1000.0),