Support all CSS units

[brson]

I think we only really us px at the moment. Make pt, em and other units work correctly everywhere.

• Distance Units: the ‘<length>’ type
  • Relative lengths
    • Font-relative lengths:
      • em
      • ex (as 0.5em)
      • ch (as 0.5em)
      • rem
    • Viewport-percentage lengths:
      • vw
      • vh
      • vmin
      • vmax
  • Absolute lengths:
    • cm
    • mm
    • in
    • pt
    • pc
    • px
• Other Units
  • Angles: the ‘<angle>’ type and:
    • deg
    • grad
    • rad
    • turn
  • Times: the ‘<time>’ type and:
    • s
    • ms
  • Frequencies: the ‘<frequency>’ type and:
    • Hz
    • kHz
  • Resolutions: the <resolution> type and:
    • dpi
    • dpcm
    • dppx

[0b10011]

em works everywhere I've noticed.

I'm also working to add support for ex at the moment, and if all goes smoothly, I'll continue on to the others. New to Rust and Servo, so it's slow going, but getting there.

List of units:
Moved to issue description (nox)

[metajack]

I believe the idea is that the style system should be normalizing all these units into a small subset. @SimonSapin is working on the new style system right now and may have more input here.

[SimonSapin]

There is no need to "add" non-length units as long as there is no property or other CSS feature that use them. My new style system already supports all absolute length units, em, and ex. (The latter is implemented as 0.5em, which is allowed the spec but is not great.)

[0b10011]

@SimonSapin Should I not bother with this issue then? Perhaps off of your branch? I implemented ex as .5em and was just gonna start investigating how to properly implement it.

If not, what's something I can help with (being new to Rust and Servo)? I don't want to start working on something else that's already being worked on. I noticed https://github.com/mozilla/servo/wiki/Work-items-for-new-contributors, but are all of these things available? Or are they being worked on without the issue being updated accordingly?

[SimonSapin]

I’m working on a new style system meant to replace rust-css and Netsurf’s libcss in servo, so any work on rust-css will probably end up duplicated. My priority is to land this new system without regressing too much, before spending much time on new features. For example, implementing ex as 0.5em is easy enough to do right now, but doing it properly requires loading fonts and is much more involved.

As to what you can help with, have a look at issues labeled E-easy.

[nox]

@SimonSapin Can this be closed?

[SimonSapin]

Yes.