Move root_font_size to the device

components/style/servo/media_queries.rs

@@ -12,7 +12,9 @@ use font_metrics::ServoMetricsProvider;
 use media_queries::MediaType;
 use parser::ParserContext;
 use properties::{ComputedValues, StyleBuilder};
+use properties::longhands::font_size;
 use std::fmt;
+use std::sync::atomic::{AtomicIsize, Ordering};
 use style_traits::{CSSPixel, ToCss};
 use style_traits::viewport::ViewportConstraints;
 use values::computed::{self, ToComputedValue};
@@ -22,12 +24,23 @@ use values::specified;
 /// is displayed in.
 ///
 /// This is the struct against which media queries are evaluated.
-#[derive(Debug, HeapSizeOf)]
+#[derive(HeapSizeOf)]
 pub struct Device {
     /// The current media type used by de device.
     media_type: MediaType,
     /// The current viewport size, in CSS pixels.
     viewport_size: TypedSize2D<f32, CSSPixel>,
+
+    /// The font size of the root element
+    /// This is set when computing the style of the root
+    /// element, and used for rem units in other elements
+    ///
+    /// When computing the style of the root element, there can't be any
+    /// other style being computed at the same time, given we need the style of
+    /// the parent to compute everything else. So it is correct to just use
+    /// a relaxed atomic here.
+    #[ignore_heap_size_of = "Pure stack type"]
+    root_font_size: AtomicIsize,
 }
 
 impl Device {
@@ -38,6 +51,7 @@ impl Device {
         Device {
             media_type: media_type,
             viewport_size: viewport_size,
+            root_font_size: AtomicIsize::new(font_size::get_initial_value().0 as isize), // FIXME(bz): Seems dubious?
         }
     }
 
@@ -49,6 +63,16 @@ impl Device {
         ComputedValues::initial_values()
     }
 
+    /// Get the font size of the root element (for rem)
+    pub fn root_font_size(&self) -> Au {
+        Au::new(self.root_font_size.load(Ordering::Relaxed) as i32)
+    }
+
+    /// Set the font size of the root element (for rem)
+    pub fn set_root_font_size(&self, size: Au) {
+        self.root_font_size.store(size.0 as isize, Ordering::Relaxed)
+    }
+
     /// Returns the viewport size of the current device in app units, needed,
     /// among other things, to resolve viewport units.
     #[inline]