1 files changed, 141 insertions, 0 deletions
diff --git a/servo/components/style/values/specified/resolution.rs b/servo/components/style/values/specified/resolution.rs
new file mode 100644
index 0000000000..74f100972a
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+++ b/servo/components/style/values/specified/resolution.rs
@@ -0,0 +1,141 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! Resolution values:
+//!
+//! https://drafts.csswg.org/css-values/#resolution
+
+use crate::parser::{Parse, ParserContext};
+use crate::values::specified::CalcNode;
+use crate::values::CSSFloat;
+use cssparser::{Parser, Token};
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+
+/// A specified resolution.
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToShmem)]
+pub struct Resolution {
+    value: CSSFloat,
+    unit: ResolutionUnit,
+    was_calc: bool,
+}
+
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
+enum ResolutionUnit {
+    /// Dots per inch.
+    Dpi,
+    /// An alias unit for dots per pixel.
+    X,
+    /// Dots per pixel.
+    Dppx,
+    /// Dots per centimeter.
+    Dpcm,
+}
+
+impl ResolutionUnit {
+    fn as_str(self) -> &'static str {
+        match self {
+            Self::Dpi => "dpi",
+            Self::X => "x",
+            Self::Dppx => "dppx",
+            Self::Dpcm => "dpcm",
+        }
+    }
+}
+
+impl Resolution {
+    /// Returns a resolution value from dppx units.
+    pub fn from_dppx(value: CSSFloat) -> Self {
+        Self {
+            value,
+            unit: ResolutionUnit::Dppx,
+            was_calc: false,
+        }
+    }
+
+    /// Returns a resolution value from dppx units.
+    pub fn from_x(value: CSSFloat) -> Self {
+        Self {
+            value,
+            unit: ResolutionUnit::X,
+            was_calc: false,
+        }
+    }
+
+    /// Returns a resolution value from dppx units.
+    pub fn from_dppx_calc(value: CSSFloat) -> Self {
+        Self {
+            value,
+            unit: ResolutionUnit::Dppx,
+            was_calc: true,
+        }
+    }
+
+    /// Convert this resolution value to dppx units.
+    pub fn dppx(&self) -> CSSFloat {
+        match self.unit {
+            ResolutionUnit::X | ResolutionUnit::Dppx => self.value,
+            _ => self.dpi() / 96.0,
+        }
+    }
+
+    /// Convert this resolution value to dpi units.
+    pub fn dpi(&self) -> CSSFloat {
+        match self.unit {
+            ResolutionUnit::Dpi => self.value,
+            ResolutionUnit::X | ResolutionUnit::Dppx => self.value * 96.0,
+            ResolutionUnit::Dpcm => self.value * 2.54,
+        }
+    }
+
+    /// Parse a resolution given a value and unit.
+    pub fn parse_dimension<'i, 't>(value: CSSFloat, unit: &str) -> Result<Self, ()> {
+        let unit = match_ignore_ascii_case! { &unit,
+            "dpi" => ResolutionUnit::Dpi,
+            "dppx" => ResolutionUnit::Dppx,
+            "dpcm" => ResolutionUnit::Dpcm,
+            "x" => ResolutionUnit::X,
+            _ => return Err(())
+        };
+        Ok(Self {
+            value,
+            unit,
+            was_calc: false,
+        })
+    }
+}
+
+impl ToCss for Resolution {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        crate::values::serialize_specified_dimension(
+            self.value,
+            self.unit.as_str(),
+            self.was_calc,
+            dest,
+        )
+    }
+}
+
+impl Parse for Resolution {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+        match *input.next()? {
+            Token::Dimension {
+                value, ref unit, ..
+            } if value >= 0. => Self::parse_dimension(value, unit)
+                .map_err(|()| location.new_custom_error(StyleParseErrorKind::UnspecifiedError)),
+            Token::Function(ref name) => {
+                let function = CalcNode::math_function(context, name, location)?;
+                CalcNode::parse_resolution(context, input, function)
+            },
+            ref t => return Err(location.new_unexpected_token_error(t.clone())),
+        }
+    }
+}