SVG text elements do not support textLength and lengthAdjust attributes

[oshmoun]

According to the specs, textLength should be a valid attribute for SVG text elements. However, it seems Weasyprint is ignoring it. The same applies for lengthAdjust.

Here's an example SVG:

<svg width="240" height="40" viewBox="0 0 240 40" xmlns="http://www.w3.org/2000/svg">
<text fill="black"><tspan x="10" y="20" textLength="20" lengthAdjust="spacingAndGlyphs">short</tspan> <tspan textLength="200" lengthAdjust="spacingAndGlyphs">long</tspan></text>
</svg>

Expected:

Result:

[liZe]

That would be a nice feature to have!

[oshmoun]

That would be a nice feature to have!

Oh definitely 😄
So if I'm understanding correctly, Weasyprint is currently lacking support of this. Would you think it's doable with the current state of Weasyprint or would it require too many things to change? I'll dig into the code and hopefully figure that out 😁

[liZe]

So if I'm understanding correctly, Weasyprint is currently lacking support of this.

That’s right.

Would you think it's doable with the current state of Weasyprint or would it require too many things to change?

It’s doable, but probably a bit complicated.

A "simple" proof of concept would be to use the width value returned here and change the letter_spacing according to the textLength value and the number of glyphs in the text string.

Don’t be afraid to try, we’re available to help if needed!

(Of course, that’s just a first step. We then would have to handle other "details" such as nested tspan tags 😱 and lengthAdjust! Let’s keep these for later…)

[oshmoun]

A "simple" proof of concept would be to use the width value returned here and change the letter_spacing according to the textLength value and the number of glyphs in the text string.

Oh that sounds quite straightforward, so basically calculate the difference between width and textLength and space the letters out so they're evenly distributed. That would implement textLength and lengthAdjust=spacing simultaneously, only spacingAndGlyphs would remain as it's probably a complex matter, as you suggest.
I'm new to this rendering stuff, guess this is a good start 😁

[oshmoun]

Implemented the PoC, here's the result for the SVG in the description:

while it works quite nicely, the spacing strategy has the unintended consequence of introducing whitespace within the words, making them unsearchable. Not sure how that could be avoided 😓

[oshmoun]

Ok I ended up also implementing spacingAndGlyphs, which avoids the whitespace issue observed in the previous comment 🥳

works pretty well!

[liZe]

That’s great, thanks a lot! 😍💜

I’ll clean a few things and get back to you soon.

If you have some motivation left, you can add some tests in test_text.py. Other tests in this file should be enough for you to understand how they work 😄. You’ll find extra tips about how to launch tests in the doc if needed! (And of course, I can add the tests myself if you don’t want to, no problem at all.)

[oshmoun]

If you have some motivation left, you can add some tests in test_text.py. Other tests in this file should be enough for you to understand how they work 😄. You’ll find extra tips about how to launch tests in the doc if needed! (And of course, I can add the tests myself if you don’t want to, no problem at all.)

I'll look into the tests today, and push them to the PR when ready 😃

[liZe]

Fixed by #1922.