Apply container offset and scroll between transform and container perspective.

third_party/WebKit/Source/core/layout/LayoutObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index 22a31999a0631cfd3d6b81222a611cbd7168140b..4f842f54b34306a39f5cf9c0abdb520d3a9d3c31 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -2302,15 +2302,16 @@ void LayoutObject::GetTransformFromContainer(
     const LayoutSize& offset_in_container,
     TransformationMatrix& transform) const {
   transform.MakeIdentity();
-  transform.Translate(offset_in_container.Width().ToFloat(),
-                      offset_in_container.Height().ToFloat());
   PaintLayer* layer = HasLayer() ? ToLayoutBoxModelObject(this)->Layer() : 0;
   if (layer && layer->Transform())
     transform.Multiply(layer->CurrentTransform());
 
+  transform.TranslateRight(offset_in_container.Width().ToFloat(),

[chrishtr, 2017/04/10 19:37:35]

I can't come up with a case where the change here made a difference.
Don't know why - it should matter which order the transform and translation
happen in.

[trchen, 2017/04/10 21:15:18]

The code here is equivalent. See explanation above.

[chrishtr, 2017/04/10 21:38:28]

Ok.

+                           offset_in_container.Height().ToFloat());
+
   if (container_object && container_object->HasLayer() &&
       container_object->Style()->HasPerspective()) {
-    // Perpsective on the container affects us, so we have to factor it in here.
+    // Perspective on the container affects us, so we have to factor it in here.
     DCHECK(container_object->HasLayer());
     FloatPoint perspective_origin =
         ToLayoutBoxModelObject(container_object)->Layer()->PerspectiveOrigin();
@@ -2318,12 +2319,11 @@ void LayoutObject::GetTransformFromContainer(
     TransformationMatrix perspective_matrix;
     perspective_matrix.ApplyPerspective(
         container_object->Style()->Perspective());
+    perspective_matrix.ApplyTransformOrigin(perspective_origin.X(),
+                                            perspective_origin.Y(), 0);
 
-    transform.TranslateRight3d(-perspective_origin.X(), -perspective_origin.Y(),
-                               0);
+    // TODO(chrishtr): This applies perspective before the transform. Why?

[trchen, 2017/04/10 21:15:19]

This lgtm. It's TransformationMatrix.h lbtm. :/

[chrishtr, 2017/04/10 21:38:28]

Removed the comment.

     transform = perspective_matrix * transform;
-    transform.TranslateRight3d(perspective_origin.X(), perspective_origin.Y(),
-                               0);
   }
 }