Giters

servo / servo

Servo, the embeddable, independent, memory-safe, modular, parallel web rendering engine

Home Page:https://servo.org

Geek Repo:Geek Repo

Github PK Tool:Github PK Tool

Stylo's Device should have access to font metrics

Loirooriol opened this issue · comments

commented

In Gecko, Device has a document member: https://searchfox.org/mozilla-central/rev/511d9c9e2eb0f2291dc2b2a5462ba054dfc2edfe/servo/components/style/gecko/media_queries.rs#37

From there is can get the nsPresContext, which is used to get the font metrics to resolve line-height:

Servo should do something similar in order to have proper support for lh units: https://bugzilla.mozilla.org/show_bug.cgi?id=1310170

I think layout2020 gets the font metrics like this:

            crate::context::with_thread_local_font_context(layout_context, |font_context| {
                get_font_for_first_font_for_style(style, font_context)
                    .map(|font| font.borrow().metrics.clone())
            });

and legacy like

pub fn font_metrics_for_style(
    font_context: &mut LayoutFontContext,
    style: crate::ServoArc<FontStyleStruct>,
) -> FontMetrics {
    let font_group = font_context.font_group(style);
    let font = font_group.borrow_mut().first(font_context);
    let font = font.as_ref().unwrap().borrow();

    font.metrics.clone()
}

where the LayoutFontContext comes from something like

                with_thread_local_font_context(self.layout_context, |font_context| {
                    inline_flow
                        .minimum_line_metrics(font_context, &node.style(self.style_context()))
                });

So it seems we need to somehow expose the LayoutContext of both 2020 and 2013 (they are different) to Device.

commented

This will likely need to be exposed to Stylo using some sort of trait, I suspect.

commented

How does servo implement stuff like ex units? Servo should have a font metrics provider that works for this, right?

commented

Looks like this is currently unsupported: #14079.

commented

I have a patch in progress for this one.