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Automatically select the range for charts in a general way

Authored by epriestley on May 8 2019, 3:55 PM.



Ref T13279. Replace the hard-coded default range with a range computed by examining the chart data.

Instead of having a "Dataset" return a blob of wire data, "Dataset" now returns a structure with raw wire data plus a range. I expect to add more structured data here in future changes (tooltip/hover event data, maybe function labels).

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epriestley created this revision.May 8 2019, 3:55 PM
epriestley requested review of this revision.May 8 2019, 3:57 PM
amckinley accepted this revision.May 21 2019, 10:30 PM
amckinley added inline comments.

Not sure where in the stack this should live, but we should probably scale y-max by 110% or something so we don't give the appearance of truncating the data (and the y-min by -110% if any data points go below 0).

This revision is now accepted and ready to land.May 21 2019, 10:30 PM

Yeah, I ideally want to try to round up, up to X%, to the nearest "nice" number, like if the range is 0-93 we show 0-100, since "100" is the nearest "nice round number" above 93. There was some simple code for this before (visual-max = actual-max * 1.2 or something) which makes the shape of the graph look good but doesn't produce the most satisfying ticks on the Y-axis or the ideally satisfying Y-max.

The algorithm for producing a "nice round number larger than X" isn't immediately intuitively obvious to me, though. And if the range is 0-100 inclusive, is it better to draw a chart with a satisfyingly round y-max, or to intentionally waste space at the top and select a dissatisfying visual y-max?

(We also don't need to tick the y-max -- we could tick at 100 and draw to 110.)