Fix Sample Clips Getting Out of Sync

[regulus79]

Fixes #8182

When #7454 was merged, the frameOffset variable inside Song::PlayPos which kept track of the actual frame position which the song was playing at relative to the last tick, was moved to Timeline. In the process, the type was inadvertently changed from float to f_cnt_t.

This caused the frame offset to be truncated ever time it was updated in Song::processNextBuffer, causing the song playback to slowly drift back ever so slightly, just a handful of frames every bar. This caused any new sample clips spawned to be created slightly late, becoming out of sync with any existing playing samples.

This PR fixes the issue by reverting the frameOffset variable type to be float again, allowing it to track sub-sample offsets over time.

[szeli1]

I have the understanding that these changes were present in lmms previously before the bug happened, therefor I approve this pull request.

[sakertooth]

Quite odd that a frame offset is a float.

Edit: Oh, it's an offset position within a frame? That makes more sense.

[sakertooth]

Code changes look good to me.

[sakertooth]

PS: I ran into a similar truncation somewhere else in the codebase, but using float caused the issue and switching to double fixed it. I have doubts that is something we need to look into though regarding this if the previous working code was using float, but maybe something to think about.

[regulus79]

Thanks for approving!

Quite odd that a frame offset is a float.

I would agree. My understanding is that because the song playback position is tracked in ticks, but frames are smaller than ticks, frameOffset keeps track of the remainder frames relative to the start of the last tick. But because the number of frames per tick isn't usually a whole number, it has to be a float.

I imagine a simpler system would be to keep track of the total frame count and simply convert it to ticks when it needs to be compared with a TimePos or something. But I'm not sure.