`On Wed, Oct 28, 2020 at 8:12 AM Daniel Thompson<daniel.thompson@linaro.org> wrote:>> On Wed, Oct 21, 2020 at 10:04:45PM -0700, Alexandru Stan wrote:> > The previous behavior was a little unexpected, its properties/problems:> > 1. It was designed to generate strictly increasing values (no repeats)> > 2. It had quantization errors when calculating step size. Resulting in> > unexpected jumps near the end of some segments.> >> > Example settings:> >       brightness-levels = <0 1 2 4 8 16 32 64 128 256>;> >       num-interpolated-steps = <16>;> >> > Whenever num-interpolated-steps was larger than the distance> > between 2 consecutive brightness levels the table would get really> > discontinuous. The slope of the interpolation would stick with> > integers only and if it was 0 the whole line segment would get skipped.> >> > The distances between 1 2 4 and 8 would be 1 (property #1 fighting us),> > and only starting with 16 it would start to interpolate properly.> >> > Property #1 is not enough. The goal here is more than just monotonically> > increasing. We should still care about the shape of the curve. Repeated> > points might be desired if we're in the part of the curve where we want> > to go slow (aka slope near 0).> >> > Problem #2 is plainly a bug. Imagine if the 64 entry was 63 instead,> > the calculated slope on the 32-63 segment will be almost half as it> > should be.> >> > The most expected and simplest algorithm for interpolation is linear> > interpolation, which would handle both problems.> > Let's just implement that!> >> > Take pairs of points from the brightness-levels array and linearly> > interpolate between them. On the X axis (what userspace sees) we'll> > now have equally sized intervals (num-interpolated-steps sized,> > as opposed to before where we were at the mercy of quantization).> >> > END>> INTERESTING.>> I guess this a copy 'n paste error from some internal log book?> Better removed... but I won't lose sleep over it.Sorry! Yeah, I mistakenly duplicated the "END" line in patman.>>> > Signed-off-by: Alexandru Stan <amstan@chromium.org>>> I've waited a bit to see how strong the feelings were w.r.t. getting rid> of the division from the table initialization. It was something I was> aware of during an earlier review but it was below my personal nitpicking> threshold (which could be badly calibrated... hence waiting). However> it's all been quiet so:>> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>>>> Daniel.Alexandru Stan (amstan)`