Auto merge of #17654 - jyc:image-orientation, r=Manishearth

Make Servo's rounding of image-orientation values agree with Gecko's, and pass orientations directly as an enum instead of as angles.

Has been reviewed: https://reviewboard.mozilla.org/r/155336/

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Bugzilla issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1355380

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4 files changed, 85 insertions, 29 deletions

diff --git a/components/style/gecko/generated/bindings.rs b/components/style/gecko/generated/bindings.rs
index 427992d8939..f5c64216008 100644
--- a/components/style/gecko/generated/bindings.rs
+++ b/components/style/gecko/generated/bindings.rs
@@ -897,7 +897,7 @@ extern "C" {
 }
 extern "C" {
     pub fn Gecko_SetImageOrientation(aVisibility: *mut nsStyleVisibility,
-                                     aRadians: f64, aFlip: bool);
+                                     aOrientation: u8, aFlip: bool);
 }
 extern "C" {
     pub fn Gecko_SetImageOrientationAsFromImage(aVisibility:
diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 13f7b130841..240139c33cb 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -3846,9 +3846,9 @@ fn static_assert() {
                     bindings::Gecko_SetImageOrientationAsFromImage(&mut self.gecko);
                 }
             },
-            T::AngleWithFlipped(ref angle, flipped) => {
+            T::AngleWithFlipped(ref orientation, flipped) => {
                 unsafe {
-                    bindings::Gecko_SetImageOrientation(&mut self.gecko, angle.radians() as f64, flipped);
+                    bindings::Gecko_SetImageOrientation(&mut self.gecko, *orientation as u8, flipped);
                 }
             }
         }
diff --git a/components/style/properties/longhand/inherited_box.mako.rs b/components/style/properties/longhand/inherited_box.mako.rs
index 772847df0ba..b6830761abf 100644
--- a/components/style/properties/longhand/inherited_box.mako.rs
+++ b/components/style/properties/longhand/inherited_box.mako.rs
@@ -68,9 +68,8 @@ ${helpers.single_keyword("image-rendering",
 
     no_viewport_percentage!(SpecifiedValue);
 
-    use std::f32::consts::PI;
-    use values::CSSFloat;
-    const TWO_PI: CSSFloat = 2.0 * PI;
+    use std::f64::consts::PI;
+    const TWO_PI: f64 = 2.0 * PI;
 
     #[derive(Clone, PartialEq, Copy, Debug)]
     #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
@@ -99,31 +98,77 @@ ${helpers.single_keyword("image-rendering",
     }
 
     pub mod computed_value {
-        use values::computed::Angle;
+        use std::fmt;
+        use style_traits::ToCss;
+        use values::specified::Angle;
+
+        #[derive(Copy, Clone, Debug, Eq, PartialEq)]
+        #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+        pub enum Orientation {
+            Angle0 = 0,
+            Angle90,
+            Angle180,
+            Angle270,
+        }
+
+        impl Orientation {
+            pub fn angle(&self) -> Angle {
+                match *self {
+                    Orientation::Angle0 => Angle::from_degrees(0.0, false),
+                    Orientation::Angle90 => Angle::from_degrees(90.0, false),
+                    Orientation::Angle180 => Angle::from_degrees(180.0, false),
+                    Orientation::Angle270 => Angle::from_degrees(270.0, false),
+                }
+            }
+        }
+
+        impl ToCss for Orientation {
+            fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+                // Should agree with Angle::to_css.
+                match *self {
+                    Orientation::Angle0 => dest.write_str("0deg"),
+                    Orientation::Angle90 => dest.write_str("90deg"),
+                    Orientation::Angle180 => dest.write_str("180deg"),
+                    Orientation::Angle270 => dest.write_str("270deg"),
+                }
+            }
+        }
 
         #[derive(Clone, PartialEq, Copy, Debug)]
         #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
         pub enum T {
             FromImage,
-            AngleWithFlipped(Angle, bool),
+            AngleWithFlipped(Orientation, bool),
         }
     }
 
+    use self::computed_value::Orientation;
+
     #[inline]
     pub fn get_initial_value() -> computed_value::T {
-        computed_value::T::AngleWithFlipped(computed::Angle::zero(), false)
+        computed_value::T::AngleWithFlipped(Orientation::Angle0, false)
     }
 
     // According to CSS Content Module Level 3:
     // The computed value of the property is calculated by rounding the specified angle
     // to the nearest quarter-turn, rounding away from 0, then moduloing the value by 1 turn.
+    // This mirrors the Gecko implementation in
+    // nsStyleImageOrientation::CreateAsAngleAndFlip.
     #[inline]
-    fn normalize_angle(angle: &computed::Angle) -> computed::Angle {
-        let radians = angle.radians();
-        let rounded_quarter_turns = (4.0 * radians / TWO_PI).round();
-        let normalized_quarter_turns = (rounded_quarter_turns % 4.0 + 4.0) % 4.0;
-        let normalized_radians = normalized_quarter_turns/4.0 * TWO_PI;
-        computed::Angle::from_radians(normalized_radians)
+    fn orientation_of_angle(angle: &computed::Angle) -> Orientation {
+        // Note that `angle` can be negative.
+        let mut rounded_angle = angle.radians64() % TWO_PI;
+        if rounded_angle < 0.0 {
+            // This computation introduces rounding error. Gecko previously
+            // didn't handle the negative case correctly; by branching we can
+            // match Gecko's behavior when it was correct.
+            rounded_angle = rounded_angle + TWO_PI;
+        }
+        if      rounded_angle < 0.25 * PI { Orientation::Angle0   }
+        else if rounded_angle < 0.75 * PI { Orientation::Angle90  }
+        else if rounded_angle < 1.25 * PI { Orientation::Angle180 }
+        else if rounded_angle < 1.75 * PI { Orientation::Angle270 }
+        else                              { Orientation::Angle0   }
     }
 
     impl ToComputedValue for SpecifiedValue {
@@ -133,11 +178,11 @@ ${helpers.single_keyword("image-rendering",
         fn to_computed_value(&self, context: &Context) -> computed_value::T {
             if let Some(ref angle) = self.angle {
                 let angle = angle.to_computed_value(context);
-                let normalized_angle = normalize_angle(&angle);
-                computed_value::T::AngleWithFlipped(normalized_angle, self.flipped)
+                let orientation = orientation_of_angle(&angle);
+                computed_value::T::AngleWithFlipped(orientation, self.flipped)
             } else {
                 if self.flipped {
-                    computed_value::T::AngleWithFlipped(computed::Angle::zero(), true)
+                    computed_value::T::AngleWithFlipped(Orientation::Angle0, true)
                 } else {
                     computed_value::T::FromImage
                 }
@@ -148,9 +193,9 @@ ${helpers.single_keyword("image-rendering",
         fn from_computed_value(computed: &computed_value::T) -> Self {
             match *computed {
                 computed_value::T::FromImage => SpecifiedValue { angle: None, flipped: false },
-                computed_value::T::AngleWithFlipped(ref angle, flipped) => {
+                computed_value::T::AngleWithFlipped(ref orientation, flipped) => {
                     SpecifiedValue {
-                        angle: Some(Angle::from_computed_value(angle)),
+                        angle: Some(orientation.angle()),
                         flipped: flipped,
                     }
                 }
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 9b08cd6e2bb..1183cbd3044 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -13,7 +13,8 @@ use media_queries::Device;
 use properties;
 use properties::{ComputedValues, StyleBuilder};
 use std::f32;
-use std::f32::consts::PI;
+use std::f64;
+use std::f64::consts::PI;
 use std::fmt;
 use style_traits::ToCss;
 use super::{CSSFloat, CSSInteger, RGBA};
@@ -313,17 +314,27 @@ impl Angle {
     /// Return the amount of radians this angle represents.
     #[inline]
     pub fn radians(&self) -> CSSFloat {
-        const RAD_PER_DEG: CSSFloat = PI / 180.0;
-        const RAD_PER_GRAD: CSSFloat = PI / 200.0;
-        const RAD_PER_TURN: CSSFloat = PI * 2.0;
+        self.radians64().min(f32::MAX as f64).max(f32::MIN as f64) as f32
+    }
+
+    /// Return the amount of radians this angle represents as a 64-bit float.
+    /// Gecko stores angles as singles, but does this computation using doubles.
+    /// See nsCSSValue::GetAngleValueInRadians.
+    /// This is significant enough to mess up rounding to the nearest
+    /// quarter-turn for 225 degrees, for example.
+    #[inline]
+    pub fn radians64(&self) -> f64 {
+        const RAD_PER_DEG: f64 = PI / 180.0;
+        const RAD_PER_GRAD: f64 = PI / 200.0;
+        const RAD_PER_TURN: f64 = PI * 2.0;
 
         let radians = match *self {
-            Angle::Degree(val) => val * RAD_PER_DEG,
-            Angle::Gradian(val) => val * RAD_PER_GRAD,
-            Angle::Turn(val) => val * RAD_PER_TURN,
-            Angle::Radian(val) => val,
+            Angle::Degree(val) => val as f64 * RAD_PER_DEG,
+            Angle::Gradian(val) => val as f64 * RAD_PER_GRAD,
+            Angle::Turn(val) => val as f64 * RAD_PER_TURN,
+            Angle::Radian(val) => val as f64,
         };
-        radians.min(f32::MAX).max(f32::MIN)
+        radians.min(f64::MAX).max(f64::MIN)
     }
 
     /// Returns an angle that represents a rotation of zero radians.