Brush inputs/settings not calibrated for viewzoom and viewrotation (ascension, direction, dab-angle, speed, et al.) about libmypaint

[achadwick]

The brush engine is currently unaware of the zoom level.

[briend]

Not sure how I closed the issue. Anyway, that makes sense. So we'd have to pass zoom level just like pressure to brush lib?

[briend]

I'm working on a branch that passes zoom and view-rotation data as input data to libmypaint. So now with the data the brush engine should be able to correct for them. I've had success correcting Direction and Ascension, and will try to correct speed next:
https://github.com/briend/libmypaint/tree/view-zoom
https://github.com/briend/mypaint/tree/view-zoom
Any help/suggestions are appreciated! I'm not a math-person so I basically trial-and-error 15 different formulas until the result is what I expect :-)

[briend]

Ok I have speed corrected for zoom in the branched in the previous post (yay!). Funny the values stay between 0 and 4 so there is no need to change the brush settings. I clamp at 4.0 just in case-- if you really whip the stylus I saw values around 5.0. I also removed the division by base_radius since that is unnecessary now.

What I didn't realize is the gamma setting isn't supposed to let you have huge values-- it's supposed to CHANGE the values more quickly (with higher gamma) and more slowly with lower gamma. When I saw speeds of over 200 I assumed the gamma was responsible for inflating the numbers but really it was just quickly reporting the actual speed (yikes!).

Here's a demo video showing a brush w/ jitter controlled by speed-- works consistently at all zoom levels!
https://www.youtube.com/watch?v=JAQ5wUKbUOw&feature=youtu.be

[briend]

community discussion here:
https://community.mypaint.org/t/zoom-and-view-rotation-corrections-rfc/465

[briend]

Changed title to reflect the scope of this issue, which I think should be tackled as a whole. I've updated the view-zoom branches to adjust for zoom(speed) and viewrotation(ascension, direction, dab angle). Please give it a try!