Ascension / Tilt does not adhere to Rotation / Flip

[t3hm00kz]

When applying Ascension / Tilt to a brush, it will not adhere to any Rotation / Flip.

REPRO:

1. Set up a brush to utilize Ascension / Tilt in some way
   - I.E.: Elliptical dab : angle > Ascension > Value: 90.00 > Output 180 / Min -180 / Max 180
   - Brushes attached are set up for Ascension / Tilt: TILT BRUSHES.zip

2. Set: 0% Rotation / Horizontal Flip disabled

3. confirm the brush adheres to the user's Ascension / tilt.

4. Set: Any non-0% Rotation or Flip enabled

5. confirm the brush adheres to the user's Ascension / tilt.

EXPECTED:
Ascension / Tilt will adhere to any Rotation / Flip

RESULTS:
Ascension / Tilt does not adjust to fit user's current Rotation / Flip

IMPACT:
User cannot effectively utilize Ascension / Tilt at any non-0% Rotation / Flip

Video attached:
https://github.com/user-attachments/assets/07e1fcd7-17e7-4c18-b868-f1ae7c12a6ad

[askmeaboutlo0m]

I've made an attempted fix. Mirroring and flipping the canvas now flip the tilt inputs, so that should now work I think. The canvas rotation is also now passed into the brush engine, which seems like it should lead to correct behavior, given what the internal values end up being, but testing it I don't know if it really is working properly. I may be misunderstanding the intended behavior though, since I never use tilt dynamics myself.

Can you test how this is working? It's available in the alpha release https://github.com/drawpile/Drawpile/releases/tag/continuous

If it doesn't behave properly, can you also try how the brushes behave in MyPaint? That is where the brush engine comes from and would help figure out if it's working properly there: https://mypaint.app/

I unfortunately can't test MyPaint properly myself because the only device I have that supports tilt is an Android tablet.

[amoruwu]

Just tested Angular Offset: View
and Angular Offset Mirrored: View
View means it offsets based on the view's rotation.
Both work great now which is great.

[t3hm00kz]

Behavior between both MyPaint and DrawPile now appear to be in parity.

... which means I've just found a bug in both

• H-Flip now functions as expected for both.
• Tilt via Angular Offset: Ascension > Random behaves as expected.
  -Brush: FanTilt.zip
• Tilt via Elliptical Dab: Angle > Ascension does not.
  - Brush: FlatTilt.zip

Apologies for morphing the bug a bit. If you'd rather I log a separate one lmk.

[askmeaboutlo0m]

Alright thanks for testing, that confirms my suspicions. I guess I'll try to pre-rotate the tilt inputs then, since the engine evidently doesn't handle it properly. It'd be consistent with how I solved mirroring and flipping since there's no other way to tell the brush engine about it. It may have knock-on effects in cases where the MyPaint engine does correctly apply the view rotation, but those are pretty obvious in the code and can be removed.

It's fine to keep it all in one ticket, since the user-facing issue is still the same.