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Catch the Beat HR affecting note placements?

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dewero
83 posts
Joined May 2013
Topic Starter
dewero
Hello everyone. I've been working on a new CTB Difficulty Calculator over the past couple of months, and I've just noticed recently that hard rock seems to randomly move certain notes in a beatmap, as stated by the wiki page:

In addition to making the player character and fruits smaller (Circle size decreased) and increasing how fast they fall (AR increase), this mod can cause ordinary fruits to veer slightly to the left or right of where they were placed on the grid, requiring the player to make more chaotic movements and to use hyperdash.
Thus, in order to make my calculator accurately rate beatmaps with HR, I'd like to know how osu! decides when and how notes are moved with hard rock, so I can properly simulate these movements in my calculator.

Thanks for the help!
MillhioreF
Pro Tester
5,004 posts
Joined July 2011
MillhioreF
Basically, it works something like this.

Notes are never moved if:
- They are part of a slider.
- The previous note came more than a second ago.

If neither of the above conditions are true, then the following rules come into play:
- Notes that are perfectly stacked on the X axis are randomly moved between 0 and 20 osupixels to either the left or the right. This is decided by a PRNG, but with a static map-specific seed for consistency.
- Notes that are almost stacked on the X axis (less than 1 osupixel apart per 3ms elapsed) have their distance doubled by moving the second note twice as far away. If doing so would put it outside the playfield boundaries, the note is not moved.

Notes are moved procedurally: if a note is moved, then the next note will decide if it should be moved based on the new position of the previous note, not the original one.

Hope this helps :)
dewero
83 posts
Joined May 2013
Topic Starter
dewero
Cool! Is there any way to determine the seed for a given beatmap?
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