style: Implement transform: perspective(none)

Differential Revision: https://phabricator.services.mozilla.com/D123350

4 files changed, 72 insertions, 19 deletions

diff --git a/components/style/values/animated/transform.rs b/components/style/values/animated/transform.rs
index 57d1900a0f9..598bf9b59a7 100644
--- a/components/style/values/animated/transform.rs
+++ b/components/style/values/animated/transform.rs
@@ -1105,8 +1105,8 @@ impl Animate for ComputedTransformOperation {
                 //    interpolated as defined in section Interpolation of
                 //    Matrices afterwards.
                 //
-                let from = create_perspective_matrix(fd.px());
-                let to = create_perspective_matrix(td.px());
+                let from = create_perspective_matrix(fd.infinity_or(|l| l.px()));
+                let to = create_perspective_matrix(td.infinity_or(|l| l.px()));
 
                 let interpolated = Matrix3D::from(from).animate(&Matrix3D::from(to), procedure)?;
 
@@ -1115,15 +1115,17 @@ impl Animate for ComputedTransformOperation {
                 // Clamp results outside of the -1 to 0 range so that we get perspective
                 // function values between 1 and infinity.
                 let used_value = if perspective_z >= 0. {
-                    std::f32::INFINITY
-                } else if perspective_z <= -1. {
-                    1.
+                    transform::PerspectiveFunction::None
                 } else {
-                    -1. / perspective_z
+                    transform::PerspectiveFunction::Length(CSSPixelLength::new(
+                        if perspective_z <= -1. {
+                            1.
+                        } else {
+                            -1. / perspective_z
+                        }
+                    ))
                 };
-                Ok(TransformOperation::Perspective(CSSPixelLength::new(
-                    used_value,
-                )))
+                Ok(TransformOperation::Perspective(used_value))
             },
             _ if self.is_translate() && other.is_translate() => self
                 .to_translate_3d()
@@ -1202,14 +1204,18 @@ impl ComputeSquaredDistance for ComputedTransformOperation {
             (
                 &TransformOperation::Perspective(ref fd),
                 &TransformOperation::Perspective(ref td),
-            ) => fd.compute_squared_distance(td),
+            ) => {
+                fd.infinity_or(|l| l.px())
+                    .compute_squared_distance(&td.infinity_or(|l| l.px()))
+            },
             (&TransformOperation::Perspective(ref p), &TransformOperation::Matrix3D(ref m)) |
             (&TransformOperation::Matrix3D(ref m), &TransformOperation::Perspective(ref p)) => {
                 // FIXME(emilio): Is this right? Why interpolating this with
                 // Perspective but not with anything else?
                 let mut p_matrix = Matrix3D::identity();
-                if p.px() >= 0. {
-                    p_matrix.m34 = -1. / p.px().max(1.);
+                let p = p.infinity_or(|p| p.px());
+                if p >= 0. {
+                    p_matrix.m34 = -1. / p.max(1.);
                 }
                 p_matrix.compute_squared_distance(&m)
             },
diff --git a/components/style/values/computed/transform.rs b/components/style/values/computed/transform.rs
index 431893973f5..5eafa0cd627 100644
--- a/components/style/values/computed/transform.rs
+++ b/components/style/values/computed/transform.rs
@@ -24,6 +24,9 @@ pub type Transform = generic::GenericTransform<TransformOperation>;
 pub type TransformOrigin =
     generic::GenericTransformOrigin<LengthPercentage, LengthPercentage, Length>;
 
+/// The computed value of the `perspective()` transform function.
+pub type PerspectiveFunction = generic::PerspectiveFunction<Length>;
+
 /// A vector to represent the direction vector (rotate axis) for Rotate3D.
 pub type DirectionVector = Vector3D<CSSFloat>;
 
@@ -517,7 +520,7 @@ impl ToAnimatedZero for TransformOperation {
                 Ok(generic::TransformOperation::Rotate(Angle::zero()))
             },
             generic::TransformOperation::Perspective(_) => Ok(
-                generic::TransformOperation::Perspective(Length::new(std::f32::INFINITY))
+                generic::TransformOperation::Perspective(generic::PerspectiveFunction::None)
             ),
             generic::TransformOperation::AccumulateMatrix { .. } |
             generic::TransformOperation::InterpolateMatrix { .. } => {
diff --git a/components/style/values/generics/transform.rs b/components/style/values/generics/transform.rs
index 95f5e999b77..92987f89fe4 100644
--- a/components/style/values/generics/transform.rs
+++ b/components/style/values/generics/transform.rs
@@ -141,6 +141,41 @@ fn is_same<N: PartialEq>(x: &N, y: &N) -> bool {
     x == y
 }
 
+/// A value for the `perspective()` transform function, which is either a
+/// non-negative `<length>` or `none`.
+#[derive(
+    Clone,
+    Debug,
+    Deserialize,
+    MallocSizeOf,
+    PartialEq,
+    Serialize,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C, u8)]
+pub enum GenericPerspectiveFunction<L> {
+    /// `none`
+    None,
+    /// A `<length>`.
+    Length(L),
+}
+
+impl<L> GenericPerspectiveFunction<L> {
+    /// Returns `f32::INFINITY` or the result of a function on the length value.
+    pub fn infinity_or(&self, f: impl FnOnce(&L) -> f32) -> f32 {
+        match *self {
+            Self::None => std::f32::INFINITY,
+            Self::Length(ref l) => f(l),
+        }
+    }
+}
+
+pub use self::GenericPerspectiveFunction as PerspectiveFunction;
+
 #[derive(
     Clone,
     Debug,
@@ -240,7 +275,7 @@ where
     ///
     /// The value must be greater than or equal to zero.
     #[css(function)]
-    Perspective(Length),
+    Perspective(GenericPerspectiveFunction<Length>),
     /// A intermediate type for interpolation of mismatched transform lists.
     #[allow(missing_docs)]
     #[css(comma, function = "interpolatematrix")]
@@ -469,9 +504,12 @@ where
                 let theta = euclid::Angle::radians(theta.radians64());
                 Transform3D::rotation(0., 0., 1., theta)
             },
-            Perspective(ref d) => {
-                let m = create_perspective_matrix(d.to_pixel_length(None)?);
-                m.cast()
+            Perspective(ref p) => {
+                let px = match p {
+                    PerspectiveFunction::None => std::f32::INFINITY,
+                    PerspectiveFunction::Length(ref p) => p.to_pixel_length(None)?,
+                };
+                create_perspective_matrix(px).cast()
             },
             Scale3D(sx, sy, sz) => Transform3D::scale(sx.into(), sy.into(), sz.into()),
             Scale(sx, sy) => Transform3D::scale(sx.into(), sy.into(), 1.),
diff --git a/components/style/values/specified/transform.rs b/components/style/values/specified/transform.rs
index ba2be4ee8d3..c10b79a089b 100644
--- a/components/style/values/specified/transform.rs
+++ b/components/style/values/specified/transform.rs
@@ -238,8 +238,14 @@ impl Transform {
                             Ok(generic::TransformOperation::SkewY(theta))
                         },
                         "perspective" => {
-                            let d = specified::Length::parse_non_negative(context, input)?;
-                            Ok(generic::TransformOperation::Perspective(d))
+                            let p = match input.try_parse(|input| specified::Length::parse_non_negative(context, input)) {
+                                Ok(p) => generic::PerspectiveFunction::Length(p),
+                                Err(..) => {
+                                    input.expect_ident_matching("none")?;
+                                    generic::PerspectiveFunction::None
+                                }
+                            };
+                            Ok(generic::TransformOperation::Perspective(p))
                         },
                         _ => Err(()),
                     };