style: Make resolutions more like the rest of the CSS values.

Bug: 1460655
Reviewed-by: xidorn
MozReview-Commit-ID: 3Gt8VX1KhjC

components/style/gecko/media_queries.rs

@@ -7,7 +7,7 @@
 use app_units::AU_PER_PX;
 use app_units::Au;
 use context::QuirksMode;
-use cssparser::{BasicParseErrorKind, Parser, Token, RGBA};
+use cssparser::{BasicParseErrorKind, Parser, RGBA};
 use euclid::Size2D;
 use euclid::TypedScale;
 use gecko::values::{convert_nscolor_to_rgba, convert_rgba_to_nscolor};
@@ -32,7 +32,7 @@ use stylesheets::Origin;
 use values::{serialize_atom_identifier, CSSFloat, CustomIdent, KeyframesName};
 use values::computed::{self, ToComputedValue};
 use values::computed::font::FontSize;
-use values::specified::{Integer, Length, Number};
+use values::specified::{Integer, Length, Number, Resolution};
 
 /// The `Device` in Gecko wraps a pres context, has a default values computed,
 /// and contains all the viewport rule state.
@@ -286,53 +286,6 @@ impl PartialEq for Expression {
     }
 }
 
-/// A resolution.
-#[derive(Clone, Debug, PartialEq, ToCss)]
-pub enum Resolution {
-    /// Dots per inch.
-    #[css(dimension)]
-    Dpi(CSSFloat),
-    /// Dots per pixel.
-    #[css(dimension)]
-    Dppx(CSSFloat),
-    /// Dots per centimeter.
-    #[css(dimension)]
-    Dpcm(CSSFloat),
-}
-
-impl Resolution {
-    fn to_dpi(&self) -> CSSFloat {
-        match *self {
-            Resolution::Dpi(f) => f,
-            Resolution::Dppx(f) => f * 96.0,
-            Resolution::Dpcm(f) => f * 2.54,
-        }
-    }
-
-    fn parse<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
-        let location = input.current_source_location();
-        let (value, unit) = match *input.next()? {
-            Token::Dimension {
-                value, ref unit, ..
-            } => (value, unit),
-            ref t => return Err(location.new_unexpected_token_error(t.clone())),
-        };
-
-        if value <= 0. {
-            return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-        }
-
-        (match_ignore_ascii_case! { &unit,
-            "dpi" => Ok(Resolution::Dpi(value)),
-            "dppx" => Ok(Resolution::Dppx(value)),
-            "dpcm" => Ok(Resolution::Dpcm(value)),
-            _ => Err(())
-        }).map_err(|()| {
-            location.new_custom_error(StyleParseErrorKind::UnexpectedDimension(unit.clone()))
-        })
-    }
-}
-
 /// A value found or expected in a media expression.
 ///
 /// FIXME(emilio): How should calc() serialize in the Number / Integer /
@@ -535,7 +488,7 @@ fn parse_feature_value<'i, 't>(
             MediaExpressionValue::IntRatio(a.value() as u32, b.value() as u32)
         },
         nsMediaFeature_ValueType::eResolution => {
-            MediaExpressionValue::Resolution(Resolution::parse(input)?)
+            MediaExpressionValue::Resolution(Resolution::parse(context, input)?)
         },
         nsMediaFeature_ValueType::eEnumerated => {
             let location = input.current_source_location();

components/style/values/computed/mod.rs

@@ -56,6 +56,7 @@ pub use self::inherited_box::{ImageOrientation, Orientation};
 #[cfg(feature = "gecko")]
 pub use self::gecko::ScrollSnapPoint;
 pub use self::rect::LengthOrNumberRect;
+pub use self::resolution::Resolution;
 pub use super::{Auto, Either, None_};
 pub use super::specified::{BorderStyle, TextDecorationLine};
 pub use self::length::{CalcLengthOrPercentage, Length, LengthOrNumber, LengthOrPercentage};
@@ -105,6 +106,7 @@ pub mod outline;
 pub mod percentage;
 pub mod position;
 pub mod rect;
+pub mod resolution;
 pub mod svg;
 pub mod table;
 pub mod text;

components/style/values/computed/resolution.rs

@@ -0,0 +1,48 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Resolution values:
+//!
+//! https://drafts.csswg.org/css-values/#resolution
+
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ToCss};
+use values::computed::{Context, ToComputedValue};
+use values::specified;
+use values::CSSFloat;
+
+/// A computed `<resolution>`.
+pub struct Resolution(CSSFloat);
+
+impl Resolution {
+    /// Returns this resolution value as dppx.
+    #[inline]
+    pub fn dppx(&self) -> CSSFloat {
+        self.0
+    }
+}
+
+impl ToComputedValue for specified::Resolution {
+    type ComputedValue = Resolution;
+
+    #[inline]
+    fn to_computed_value(&self, _: &Context) -> Self::ComputedValue {
+        Resolution(self.to_dppx())
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        specified::Resolution::Dppx(computed.dppx())
+    }
+}
+
+impl ToCss for Resolution {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        self.dppx().to_css(dest)?;
+        dest.write_str("dppx")
+    }
+}

components/style/values/specified/mod.rs

@@ -61,6 +61,7 @@ pub use self::list::Quotes;
 pub use self::list::ListStyleType;
 pub use self::outline::OutlineStyle;
 pub use self::rect::LengthOrNumberRect;
+pub use self::resolution::Resolution;
 pub use self::percentage::Percentage;
 pub use self::position::{GridAutoFlow, GridTemplateAreas, Position};
 pub use self::position::{PositionComponent, ZIndex};
@@ -105,6 +106,7 @@ pub mod outline;
 pub mod percentage;
 pub mod position;
 pub mod rect;
+pub mod resolution;
 pub mod source_size_list;
 pub mod svg;
 pub mod table;

components/style/values/specified/resolution.rs

@@ -0,0 +1,73 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Resolution values:
+//!
+//! https://drafts.csswg.org/css-values/#resolution
+
+use cssparser::{Parser, Token};
+use parser::{Parse, ParserContext};
+use style_traits::{ParseError, StyleParseErrorKind};
+use values::CSSFloat;
+
+/// A specified resolution.
+#[derive(Clone, Debug, PartialEq, ToCss)]
+pub enum Resolution {
+    /// Dots per inch.
+    #[css(dimension)]
+    Dpi(CSSFloat),
+    /// Dots per pixel.
+    #[css(dimension)]
+    Dppx(CSSFloat),
+    /// Dots per centimeter.
+    #[css(dimension)]
+    Dpcm(CSSFloat),
+}
+
+impl Resolution {
+    /// Convert this resolution value to dppx units.
+    pub fn to_dppx(&self) -> CSSFloat {
+        match *self {
+            Resolution::Dppx(f) => f,
+            _ => self.to_dpi() / 96.0,
+        }
+    }
+
+    /// Convert this resolution value to dpi units.
+    pub fn to_dpi(&self) -> CSSFloat {
+        match *self {
+            Resolution::Dpi(f) => f,
+            Resolution::Dppx(f) => f * 96.0,
+            Resolution::Dpcm(f) => f * 2.54,
+        }
+    }
+}
+
+impl Parse for Resolution {
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+        let (value, unit) = match *input.next()? {
+            Token::Dimension {
+                value, ref unit, ..
+            } => (value, unit),
+            ref t => return Err(location.new_unexpected_token_error(t.clone())),
+        };
+
+        if value <= 0. {
+            return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+        }
+
+        match_ignore_ascii_case! { &unit,
+            "dpi" => Ok(Resolution::Dpi(value)),
+            "dppx" => Ok(Resolution::Dppx(value)),
+            "dpcm" => Ok(Resolution::Dpcm(value)),
+            _ => Err(location.new_custom_error(
+                StyleParseErrorKind::UnexpectedDimension(unit.clone())
+            )),
+        }
+    }
+}