Scrolling Versus Flat Rotation

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Scrolling Versus Flat Rotation

Postby Enjay » Sun Jan 03, 2021 2:02 pm

Probably not a bug - but may as well report. Noticed in 4.5.0 but this goes back a long way.

When working on a map (not mine) that was using a line type 223 to scroll a floor I noticed that the floor was moving south even though the line was set to scroll north. I checked and the floor of the sector had been rotated 180°. "Fair enough" I thought, but then I did a bit more digging and noticed that the results were less predictable than I expected.

If a floor is rotated 90° or 270°, the floor still scrolls to the map's north.
If the floor is rotated 45° or 225° then the floor will scroll west.
If the floor is rotated 135°or 315° then the floor will scroll east.



So, I have no idea what is meant to be happening here.

The test map shows the effect. All of the pits are set to scroll by the same line - a line special 223 tagged to any sector with tag 1 and set to scroll the floor north at normal speed. The red triangles on the floor show the rotation of each sector (the top of the flat on the floor is pointing the same way as the arrow). The blue letters show NESW with respect to the map.
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Re: Scrolling Versus Flat Rotation

Postby Graf Zahl » Wed May 19, 2021 11:52 am

Don't. Even. Start.

Yes, it's a mess and no, it's not fixable without breaking lots of stuff.
The entire flat transformation code was not done with a mathematical approach. It was all implemented ad-hoc in the software renderer but the end result is a bit, let's say 'chaotic'...
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Re: Scrolling Versus Flat Rotation

Postby Gez » Wed May 19, 2021 12:51 pm

That's the kind of things that will eventually result in brand new scrolling and/or rotation properties, or perhaps a MAPINFO flag or something. Not now though.
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Re: Scrolling Versus Flat Rotation

Postby Graf Zahl » Wed May 19, 2021 12:55 pm

Indeed. The only way to fix it would be to scrap the old code and implement something sane - like building a texture matrix out of separate transformations. Then the modders could set this up as they like.
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