Fix overlapping auto-generated ticks on time scale

[kurkle]

Account for margins in getLabelCapacity

Pen PR
Pen master

Fixes: #6109

[kurkle]

Updated solution, use margins (provided here) instead of -1

[nagix]

#5961 addresses the same issue in

Chart.js/src/core/core.scale.js

Lines 436 to 443 in 8925eed

	// Estimate the width of each grid based on the canvas width, the maximum
	// label width and the number of tick intervals
	maxWidth = Math.min(me.maxWidth, me.chart.width - maxLabelWidth);
	tickWidth = options.offset ? me.maxWidth / ticks.length : maxWidth / (ticks.length - 1);
	// Allow 3 pixels x2 padding either side for label readability
	if (maxLabelWidth + 6 > tickWidth) {
	tickWidth = maxWidth / (ticks.length - (options.offset ? 0.5 : 1));

[nagix]

I think it is difficult to get tickWidth without knowing the maximum width of tick labels because the left and right padding are added based on it.

[kurkle]

Limited this change to getLabelCapacity, so we don't have overlap in PR's.

[nagix]

Well, I see... this is called before calculateTickRotation and timestamp ticks are generated so as not to overlap each other or to be rotated.

[simonbrunel]

@kurkle this PR looks fine, should we get it merged?

[benmccann]

@kurkle this PR will need to be rebased

[benmccann]

Too many labels are currently being generated because padding is not being considered when generating the labels and then padding is calculated later.

The right solution to this is to probably to calculate those values together or set a maximum padding value and use that here. I don't think the solution is to use some other value in place of padding. It seems like we're just getting lucky that's working out, so I would want to see more explanation around why that's the right thing to do.

scaleMargin is defined as:

var scaleMargin = {
	left: Math.max(outerBoxSizes.left, maxPadding.left),
	right: Math.max(outerBoxSizes.right, maxPadding.right),
};

maxPadding isn't really correct because we should use the padding for this scale and not the maximum padding of all the scales. I think maybe maxPadding is 0 at this point in the code? outerBoxSizes is defined as helpers.options.toPadding(layoutOptions.padding); though the default layout.padding is 0 so it doesn't seem like that should have an effect either. The layout and tick generation/rotation code is quite convoluted and I'm afraid this is making it harder to understand

I have a branch on my machine locally that is replacing the whole autotick generation for the time scale as suggested by @simonbrunel and described in #4612. I think it would fix the issue this is addressing. I haven't been very motivated lately to open new PRs though because it seems like there's a backlog of unreviewed PRs and if I open new PRs it's just going to push my controller defaults PR further down the list and make it take longer to get it merged. In either case I still have a few more edge cases I need to fix before sending