Scale.log fixes

[berekuk]

Fixes #2031.

Without a given min and max value in the scale, at certain widths, it doesn't show any axis ticks.
Note: This error only appears for me when the dist is wide enough. When it's under ~600px, it looks fine.
Another note: When hovering, I often see no number, just an empty box.

The root cause for this is that d3.scaleLog().ticks() and d3.scaleLog.tickFormat() are special.

Full docs: https://github.com/d3/d3-scale/tree/main#log_ticks

I'll try to explain what's going on.

D3 scales have two methods, .ticks(count) and .tickFormat(count, specifier). First one outputs an array of ticks to render, and second one return a format function that turns values into strings.

There are two modes for .ticks(count) on log scales:

1. Output powers of base only, if count < number of powers of base that fit in the domain.

Example:

> scaleLog().domain([5,12000]).ticks(3)
[ 10, 100, 1000, 10000 ]

2. Output all steps between different powers of base, if count is greater than that.

Example:

> scaleLog().domain([5,12000]).ticks(4)
[
     5,    6,     7,    8,    9,   10,
    20,   30,    40,   50,   60,   70,
    80,   90,   100,  200,  300,  400,
   500,  600,   700,  800,  900, 1000,
  2000, 3000,  4000, 5000, 6000, 7000,
  8000, 9000, 10000
]

(I think there might be off-by-one error here in d3's implementation, but it's not very important; d3.ticks() is never guaranteed to be precise)

Since the second mode outputs a lot of ticks, and ticks in [5..10] range are close to each other, tickFormat() returns an empty string for some ticks.

This affects both hover values and actual ticks.

For hovers, there's a special mode for tickFormat, tickFormat(Infinity), that I now use in drawCursorLines.

For tick labels, the problem was that we have our own algorithm for fitting labels in drawAxes, which forces labels to never overlap. But it could be unlucky and pick only the ticks that are empty. (I'm not sure about the details, but skipping empty labels helped.)

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[berekuk]

This is an interesting bug, and it won't be easy to fix:

It's because we convert distributions to pointsets to render them, but pointsets are not scale-aware and pick x points based on PDF.

I guess this means that x.distribution.pointSet(environment) transformation in DistributionsChart is wrong and we should handle this differently, in scale-aware fashion:

• measure PDF for equidistant points on X scale for symbolic dists
• show histograms for samplesets?..
• there's not much we can do for pointsets if their X points are a bad fit for the given scale

[berekuk]

For min < 0 in Scale.log, I now throw an error in Squiggle.

This also fixes #1798. (I throw an error when min >= max; note: this might break some existing Squiggle models).

[berekuk]

  /**
  Here, there could be a better error message.
  For example, "Min must be over 0 for log scale."
*/
  invalidWithNumericFn: Plot.numericFn(
    { fn: {|e|e}, xScale: Scale.log({ min: -1, max: 10 }) }
  )

This is now also a global runtime error.

[berekuk]

For Scale.symlog, the fix is kinda hard and not worth doing it right now; I've filed a separate #2036 for it to do later.

[OAGr]

Neat, it seems much better.

One small issue is that when the dists are very wide, it shows both the orders of magnitude of 1 and of 2, which looks a bit awkward. I imagine this would be a pain to fix though, I probably wouldn't worry about it now.

[OAGr]

Seems good! I like the functionality - code generally looks okay, though I don't understand d3 as well.

[OAGr]

Kudos for figuring this out, seems gnarly.

[OAGr]

This also fixes #1798. (I throw an error when min >= max; note: this might break some existing Squiggle models).

It seems like that issue is not totally fixed - in the case that there's a min but no max.

d2 = Plot.dist({
dist: normal(0,1),
xScale: Scale.linear({ min: 100 })
})