colorbar draws outside the bounds

[hellochar]

Hey Plotly team,

Small bug - sometimes, depending on the layout's height/vertical margins, one of the colorbar's .cbfill will get drawn outside the outline (see http://codepen.io/hellochar/pen/JREjyv):

Looks like it's only off by 1 pixel:

It is a noticeable artifact that sometimes appears in our charts. Any ideas what's going on here? Happy to submit a PR as well if someone could help me understand the code at
https://github.com/plotly/plotly.js/blob/master/src/components/colorbar/draw.js#L348

Thanks,
Xiaohan

[etpinard]

Thanks for the report.

[andi1984]

When yanchor: 'bottom' is used it is off by far more pixels also overlapping with mode bar. So this mode is pretty much not usable at the moment. It should simply set y=0 on this mode.

[alexcjohnson]

@etpinard pointed out this issue when I mentioned a related one during #1906, so I might as well combine them and tackle them simultaneously:

we're not doing crisp rendering of colorbars - particularly the outlines, but line levels should probably be crisp too

[alexcjohnson]

Looks like the original issue is masked in v1.29.0 - I suspect the tweaks in #1854 result in the outline covering the out-of-place bar - but there's still a y="-1" bar sometimes so I suspect it could become visible in certain cases. Frankly the whole concept of constructing our colorbars from 256 overlapping bars (regardless of how many pixels tall the bar is) seems a bit silly, I'm going to try to replace it with a simple gradient fill.

[alexcjohnson]

A somewhat urgent aspect of this: lines in the colorbar with the default width of 0.5 just started to disappear for me:

This only seems to be happening in Chrome on mac on my non-retina second screen. (I can't reproduce this even in ostensibly the same version of chrome on browserstack...) The lines still appear on my retina screen, and in other browsers. And they reappear if I give the lines any tilt away from horizontal, a somewhat different alignment relative to the edge of a pixel, or a width > 0.5px (even 0.51px). Another overly eager optimization by chrome? Or perhaps it somehow came in with the latest Mac OS update that I installed this morning? I don't think chrome updated in the last few days, and I'm quit confident this looked fine at the end of last week for me.

[rreusser]

@alexcjohnson This page: https://rreusser.github.io/plotly-mock-viewer/#contour_heatmap_coloring
Shows this for me (albeit on a retina screen):

What do you see? Chrome doesn't appear to have just updated for me.

[alexcjohnson]

@rreusser Yep, I see the missing lines there too.

[rreusser]

Good to know. Just wanted to be 100% sure we were all looking at identically the same code. I have a non-retina screen back at home that I can check out tonight. Anyone else able to confirm?

[rreusser]

Solves it, of course, but not a solution…

[alexcjohnson]

possibly - crispEdges is what I was going to do to fix the other part of this anyway - just worried that this will lead to other instances where the line gets completely deleted too - typically that's even easier to do crisp than non-crisp.

[alexcjohnson]

My chrome just updated from v59 to v60 and these artifacts (along with a bunch of related antialiasing failures I've noticed) seem to have been fixed. So the y="-1" issue and crisp rendering change are still open but unless other people report these missing lines and other failures I think this is no longer urgent.