Account for character descenders in text-radial-offset

[tristen]

Motivation

Like text-offset that accepts number or an array of two numbers that adjusts the x and y coordinates, it would be great if text-radial-offset allowed the same functionality. That would account for the extra distance top positioned labels need for characters with descenders (i.e g, p, q):

Design Alternatives

Not provide top as a list of possible positions to text-variable-anchor but that's a little limiting.

Design

{
  text-radial-offset: [0.5, 1] // x, y
}

[asheemmamoowala]

@tristen Are you proposing that the array takes only 2 values -[a, b], where a is the offset applied to all non-top anchor values, and b is applied only to top ?

This would be very confusing to document and explain. For example, when text-variable-anchor: ["top"] , the single value should be used, but changing it to text-variable-anchor: ["top", right] would require switching to an array [ <right_offset>, <top_offset>].

What if instead auto justification took into account the full height of symbols so that it anchors to the bottom of glyhps before adding the text-radial-offset value?

cc @vakila @ansis

[tristen]

This would be very confusing to document and explain. For example, when text-variable-anchor: ["top"] , the single value should be used, but changing it to text-variable-anchor: ["top", right] would require switching to an array [ <right_offset>, <top_offset>].

Good point.

What if instead auto justification took into account the full height of symbols so that it anchors to the bottom of glyhps before adding the text-radial-offset value?

👍

[mapcarta]

Yes this is needed. One way to do this without confusion is to have the 'text-radial-offset' array contain either exactly two or four elements:

• An array with two elements would specify the vertical (top and bottom) and horizontal (left and right) spacing, always in that order.
• An array with four elements would specify the top, right, bottom and left offsets, always in that order.

This way 'text-variable-anchor' could be changed without any trouble.

What if instead auto justification took into account the full height of symbols so that it anchors to the bottom of glyhps before adding the text-radial-offset value?

I agree this would be a far more elegant and desirable solution if it is possible.

[mapcarta]

I believe the underlying problem is that many of the fonts themselves to not seem to be properly vertically centered. While some fonts such as the default DIN Offc Pro and Open Sans seems to be properly centered, others such as Ubuntu and Lato seem to be higher than center. If for example the offset is set based off of either a default top or bottom anchor location, all of the other anchor locations will have incorrect spacing.

Perhaps there should be no need for this feature if font centering is fixed? #191

[chloekraw]

Capturing from chat with @tristen, I'm removing the high priority label because we can work around this issue by not using "top" as an anchor position for release-r, making #8583 and #8527 higher priority for release-r.

@asheemmamoowala @pozdnyakov @alexshalamov @ansis