Bug 1458927: Fix perspective squared distance computation. r=hiro

MozReview-Commit-ID: YwjTheRonB

--HG--
extra : rebase_source : d3734aad5d37dda1ccaf24f1f84e2f0972e45f5d

dom/animation/test/mozilla/test_distance_of_transform.html

@@ -192,7 +192,7 @@ test(function(t) {
   var dist = getDistance(target, 'transform',
                          'perspective(128px)',
                          'none');
-  assert_equals(dist, 1/128, 'distance of perspective');
+  assert_equals(dist, 128, 'distance of perspective');
 }, 'Test distance of perspective function and none');
 
 test(function(t) {
@@ -202,7 +202,7 @@ test(function(t) {
   var dist = getDistance(target, 'transform',
                          'perspective(128px)',
                          'perspective(0)');
-  assert_equals(dist, 1/128, 'distance of perspective');
+  assert_equals(dist, 128, 'distance of perspective');
 }, 'Test distance of perspective function and an invalid perspective');
 
 test(function(t) {
@@ -210,7 +210,7 @@ test(function(t) {
   var dist = getDistance(target, 'transform',
                          'perspective(128px)',
                          'perspective(1024px)');
-  assert_equals(dist, 1/128 - 1/1024, 'distance of perspective');
+  assert_equals(dist, 1024 - 128, 'distance of perspective');
 }, 'Test distance of perspective functions');
 
 test(function(t) {

servo/components/style/properties/helpers/animated_properties.mako.rs

@@ -2632,16 +2632,7 @@ impl ComputeSquaredDistance for ComputedTransformOperation {
                 &TransformOperation::Perspective(ref fd),
                 &TransformOperation::Perspective(ref td),
             ) => {
-                let mut fd_matrix = Matrix3D::identity();
-                let mut td_matrix = Matrix3D::identity();
-                if fd.px() > 0. {
-                    fd_matrix.m34 = -1. / fd.px();
-                }
-
-                if td.px() > 0. {
-                    td_matrix.m34 = -1. / td.px();
-                }
-                fd_matrix.compute_squared_distance(&td_matrix)
+                fd.compute_squared_distance(td)
             }
             (
                 &TransformOperation::Perspective(ref p),