style: Return an infinite perspective in TransformOperation::Perspective::to_animated_zero

Differential Revision: https://phabricator.services.mozilla.com/D122919

components/style/values/animated/transform.rs

@@ -1112,8 +1112,12 @@ impl Animate for ComputedTransformOperation {
 
                 let decomposed = decompose_3d_matrix(interpolated)?;
                 let perspective_z = decomposed.perspective.2;
-                let used_value = if perspective_z == 0. {
+                // Clamp results outside of the -1 to 0 range so that we get perspective
-                    0.
+                // function values between 1 and infinity.
+                let used_value = if perspective_z >= 0. {
+                    std::f32::INFINITY
+                } else if perspective_z <= -1. {
+                    1.
                 } else {
                     -1. / perspective_z
                 };

components/style/values/computed/transform.rs

@@ -516,8 +516,8 @@ impl ToAnimatedZero for TransformOperation {
             generic::TransformOperation::Rotate(_) => {
                 Ok(generic::TransformOperation::Rotate(Angle::zero()))
             },
-            generic::TransformOperation::Perspective(ref l) => Ok(
+            generic::TransformOperation::Perspective(_) => Ok(
-                generic::TransformOperation::Perspective(l.to_animated_zero()?),
+                generic::TransformOperation::Perspective(Length::new(std::f32::INFINITY))
             ),
             generic::TransformOperation::AccumulateMatrix { .. } |
             generic::TransformOperation::InterpolateMatrix { .. } => {

components/style/values/generics/transform.rs

@@ -583,10 +583,10 @@ impl<T: ToMatrix> Transform<T> {
 /// Return the transform matrix from a perspective length.
 #[inline]
 pub fn create_perspective_matrix(d: CSSFloat) -> Transform3D<CSSFloat> {
-    if d < 0.0 {
+    if d.is_finite() {
-        Transform3D::identity()
-    } else {
         Transform3D::perspective(d.max(1.))
+    } else {
+        Transform3D::identity()
     }
 }