style: Fix clamping on animations for fort-style.

Bug: 1455358
Reviewed-by: xidorn
MozReview-Commit-ID: Awyub0dMOmq

components/style/properties/longhand/font.mako.rs

@@ -20,8 +20,7 @@ ${helpers.predefined_type(
     "FontStyle",
     initial_value="computed::FontStyle::normal()",
     initial_specified_value="specified::FontStyle::normal()",
-    # FIXME(emilio): This won't handle clamping correctly.
+    animation_value_type="FontStyle",
-    animation_value_type="ComputedValue",
     flags="APPLIES_TO_FIRST_LETTER APPLIES_TO_FIRST_LINE APPLIES_TO_PLACEHOLDER",
     spec="https://drafts.csswg.org/css-fonts/#propdef-font-style",
     servo_restyle_damage="rebuild_and_reflow",

components/style/values/computed/angle.rs

@@ -64,6 +64,12 @@ impl Angle {
         radians.min(f64::MAX).max(f64::MIN)
     }
 
+    /// Return the value in degrees.
+    pub fn degrees(&self) -> f32 {
+        use std::f32::consts::PI;
+        self.radians() * 360. / (2. * PI)
+    }
+
     /// <https://drafts.csswg.org/css-transitions/#animtype-number>
     #[inline]
     fn animate_fallback(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {

components/style/values/computed/font.rs

@@ -838,11 +838,34 @@ impl ToComputedValue for specified::MozScriptLevel {
     }
 }
 
+/// A wrapper over an `Angle`, that handles clamping to the appropriate range
+/// for `font-style` animation.
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss)]
+pub struct FontStyleAngle(pub Angle);
+
+impl ToAnimatedValue for FontStyleAngle {
+    type AnimatedValue = Angle;
+
+    #[inline]
+    fn to_animated_value(self) -> Self::AnimatedValue {
+        self.0
+    }
+
+    #[inline]
+    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
+        FontStyleAngle(Angle::Deg(
+            animated.degrees()
+                .min(specified::FONT_STYLE_OBLIQUE_MAX_ANGLE_DEGREES)
+                .max(specified::FONT_STYLE_OBLIQUE_MIN_ANGLE_DEGREES)
+        ))
+    }
+}
+
 /// The computed value of `font-style`.
 ///
 /// FIXME(emilio): Angle should be a custom type to handle clamping during
 /// animation.
-pub type FontStyle = generics::FontStyle<Angle>;
+pub type FontStyle = generics::FontStyle<FontStyleAngle>;
 
 impl FontStyle {
     /// The `normal` value.
@@ -855,8 +878,8 @@ impl FontStyle {
     ///
     /// https://drafts.csswg.org/css-fonts-4/#valdef-font-style-oblique-angle
     #[inline]
-    pub fn default_angle() -> Angle {
+    fn default_angle() -> FontStyleAngle {
-        Angle::Deg(specified::DEFAULT_FONT_STYLE_OBLIQUE_ANGLE_DEGREES)
+        FontStyleAngle(Angle::Deg(specified::DEFAULT_FONT_STYLE_OBLIQUE_ANGLE_DEGREES))
     }
 
 

components/style/values/specified/angle.rs

@@ -110,8 +110,7 @@ impl Angle {
     /// Returns the amount of degrees this angle represents.
     #[inline]
     pub fn degrees(self) -> f32 {
-        use std::f32::consts::PI;
+        self.value.degrees()
-        self.radians() * 360. / (2. * PI)
     }
 
     /// Returns `0deg`.

components/style/values/specified/font.rs

@@ -19,7 +19,7 @@ use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
 use values::CustomIdent;
 use values::computed::{Angle as ComputedAngle, Percentage as ComputedPercentage};
 use values::computed::{font as computed, Context, Length, NonNegativeLength, ToComputedValue};
-use values::computed::font::{FamilyName, FontFamilyList, SingleFontFamily};
+use values::computed::font::{FamilyName, FontFamilyList, FontStyleAngle, SingleFontFamily};
 use values::generics::NonNegative;
 use values::generics::font::{self as generics, FeatureTagValue, FontSettings, FontTag};
 use values::generics::font::{KeywordInfo as GenericKeywordInfo, KeywordSize, VariationValue};
@@ -241,7 +241,7 @@ impl ToComputedValue for SpecifiedFontStyle {
             generics::FontStyle::Normal => generics::FontStyle::Normal,
             generics::FontStyle::Italic => generics::FontStyle::Italic,
             generics::FontStyle::Oblique(ref angle) => {
-                generics::FontStyle::Oblique(Self::compute_angle(angle))
+                generics::FontStyle::Oblique(FontStyleAngle(Self::compute_angle(angle)))
             }
         }
     }
@@ -251,7 +251,7 @@ impl ToComputedValue for SpecifiedFontStyle {
             generics::FontStyle::Normal => generics::FontStyle::Normal,
             generics::FontStyle::Italic => generics::FontStyle::Italic,
             generics::FontStyle::Oblique(ref angle) => {
-                generics::FontStyle::Oblique(Angle::from_computed_value(angle))
+                generics::FontStyle::Oblique(Angle::from_computed_value(&angle.0))
             }
         }
     }