Fixed scaling artefacts in paint worklets caused by zoom and hidpi.

components/style/context.rs

@@ -11,6 +11,7 @@ use bloom::StyleBloom;
 use cache::LRUCache;
 use data::{EagerPseudoStyles, ElementData};
 use dom::{OpaqueNode, TNode, TElement, SendElement};
+use euclid::ScaleFactor;
 use euclid::Size2D;
 use fnv::FnvHashMap;
 use font_metrics::FontMetricsProvider;
@@ -27,6 +28,8 @@ use std::fmt;
 use std::ops;
 #[cfg(feature = "servo")] use std::sync::Mutex;
 #[cfg(feature = "servo")] use std::sync::mpsc::Sender;
+use style_traits::CSSPixel;
+use style_traits::DevicePixel;
 use stylist::Stylist;
 use thread_state;
 use time;
@@ -152,6 +155,11 @@ impl<'a> SharedStyleContext<'a> {
     pub fn viewport_size(&self) -> Size2D<Au> {
         self.stylist.device().au_viewport_size()
     }
+
+    /// The device pixel ratio
+    pub fn device_pixel_ratio(&self) -> ScaleFactor<f32, CSSPixel, DevicePixel> {
+        self.stylist.device().device_pixel_ratio()
+    }
 }
 
 /// The structure holds various intermediate inputs that are eventually used by

components/style/gecko/media_queries.rs

@@ -4,9 +4,11 @@
 
 //! Gecko's media-query device and expression representation.
 
+use app_units::AU_PER_PX;
 use app_units::Au;
 use context::QuirksMode;
 use cssparser::{CssStringWriter, Parser, RGBA, Token, BasicParseError};
+use euclid::ScaleFactor;
 use euclid::Size2D;
 use font_metrics::get_metrics_provider_for_product;
 use gecko::values::convert_nscolor_to_rgba;
@@ -25,6 +27,7 @@ use std::fmt::{self, Write};
 use std::sync::atomic::{AtomicBool, AtomicIsize, Ordering};
 use str::starts_with_ignore_ascii_case;
 use string_cache::Atom;
+use style_traits::{CSSPixel, DevicePixel};
 use style_traits::{ToCss, ParseError, StyleParseError};
 use style_traits::viewport::ViewportConstraints;
 use values::{CSSFloat, specified};
@@ -153,6 +156,15 @@ impl Device {
         })
     }
 
+    /// Returns the device pixel ratio.
+    pub fn device_pixel_ratio(&self) -> ScaleFactor<f32, CSSPixel, DevicePixel> {
+        let override_dppx = self.pres_context().mOverrideDPPX;
+        if override_dppx > 0.0 { return ScaleFactor::new(override_dppx); }
+        let au_per_dpx = self.pres_context().mCurAppUnitsPerDevPixel as f32;
+        let au_per_px = AU_PER_PX as f32;
+        ScaleFactor::new(au_per_px / au_per_dpx)
+    }
+
     /// Returns whether document colors are enabled.
     pub fn use_document_colors(&self) -> bool {
         self.pres_context().mUseDocumentColors() != 0

components/style/servo/media_queries.rs

@@ -7,7 +7,7 @@
 use app_units::Au;
 use context::QuirksMode;
 use cssparser::{Parser, RGBA};
-use euclid::{Size2D, TypedSize2D};
+use euclid::{ScaleFactor, Size2D, TypedSize2D};
 use font_metrics::ServoMetricsProvider;
 use media_queries::MediaType;
 use parser::ParserContext;
@@ -16,7 +16,7 @@ use properties::longhands::font_size;
 use selectors::parser::SelectorParseError;
 use std::fmt;
 use std::sync::atomic::{AtomicBool, AtomicIsize, Ordering};
-use style_traits::{CSSPixel, ToCss, ParseError};
+use style_traits::{CSSPixel, DevicePixel, ToCss, ParseError};
 use style_traits::viewport::ViewportConstraints;
 use values::computed::{self, ToComputedValue};
 use values::specified;
@@ -31,6 +31,8 @@ pub struct Device {
     media_type: MediaType,
     /// The current viewport size, in CSS pixels.
     viewport_size: TypedSize2D<f32, CSSPixel>,
+    /// The current device pixel ratio, from CSS pixels to device pixels.
+    device_pixel_ratio: ScaleFactor<f32, CSSPixel, DevicePixel>,
 
     /// The font size of the root element
     /// This is set when computing the style of the root
@@ -51,11 +53,13 @@ pub struct Device {
 impl Device {
     /// Trivially construct a new `Device`.
     pub fn new(media_type: MediaType,
-               viewport_size: TypedSize2D<f32, CSSPixel>)
+               viewport_size: TypedSize2D<f32, CSSPixel>,
+               device_pixel_ratio: ScaleFactor<f32, CSSPixel, DevicePixel>)
                -> Device {
         Device {
             media_type: media_type,
             viewport_size: viewport_size,
+            device_pixel_ratio: device_pixel_ratio,
             root_font_size: AtomicIsize::new(font_size::get_initial_value().0 as isize), // FIXME(bz): Seems dubious?
             used_root_font_size: AtomicBool::new(false),
         }
@@ -99,6 +103,11 @@ impl Device {
         self.viewport_size
     }
 
+    /// Returns the device pixel ratio.
+    pub fn device_pixel_ratio(&self) -> ScaleFactor<f32, CSSPixel, DevicePixel> {
+        self.device_pixel_ratio
+    }
+
     /// Take into account a viewport rule taken from the stylesheets.
     pub fn account_for_viewport_rule(&mut self, constraints: &ViewportConstraints) {
         self.viewport_size = constraints.size;