Apply container offset and scroll between transform and container perspective.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1150 matching lines @@
   LayoutRect result = LayoutRect(LayoutRect::InfiniteIntRect());
   if (ShouldClipOverflow())
     result = OverflowClipRect(LayoutPoint());
 
   if (HasClip())
     result.Intersect(ClipRect(LayoutPoint()));
 
   return result;
 }
 
+bool LayoutBox::MapVisualRectToContainer(
+    const LayoutObject* container_object,
+    const LayoutPoint& container_offset,
+    const LayoutObject* ancestor,
+    VisualRectFlags visual_rect_flags,
+    TransformState& transform_state) const {
+  bool preserve3D = container_object->Style()->Preserves3D();
+
+  TransformState::TransformAccumulation accumulation =
+      preserve3D ? TransformState::kAccumulateTransform
+                 : TransformState::kFlattenTransform;
+
+  // If there is no transform on this box, adjust for container offset and
+  // container scrolling, then apply container clip.
+  if (!ShouldUseTransformFromContainer(container_object)) {
+    transform_state.MoveBy(container_offset, accumulation);
+    if (container_object->IsBox() && container_object != ancestor &&
+        !ToLayoutBox(container_object)
+             ->MapScrollingContentsRectToBoxSpace(transform_state, accumulation,
+                                                  visual_rect_flags))
+      return false;
+    return true;
+  }
+
+  // Otherwise, apply the following:
+  // 1. Transform.
+  // 2. Container offset.
+  // 3. Container scroll offset.
+  // 4. Perspective applied by container.
+  // 5. Transform flattening.
+  // 6. Expansion for pixel snapping.
+  // 7. Container clip.
+
+  // 1. Transform.
+  TransformationMatrix transform;
+  if (Layer() && Layer()->Transform())
+    transform.Multiply(Layer()->CurrentTransform());
+
+  // 2. Container offset.
+  transform.TranslateRight(container_offset.X().ToFloat(),
+                           container_offset.Y().ToFloat());
+
+  // 3. Container scroll offset.
+  if (container_object->IsBox() && container_object != ancestor &&
+      container_object->HasOverflowClip()) {
+    IntSize offset = -ToLayoutBox(container_object)->ScrolledContentOffset();
+    transform.TranslateRight(offset.Width(), offset.Height());
+  }
+
+  // 4. Perspective applied by container.
+  if (container_object && container_object->HasLayer() &&
+      container_object->Style()->HasPerspective()) {
+    // 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();
+
+    TransformationMatrix perspective_matrix;
+    perspective_matrix.ApplyPerspective(
+        container_object->Style()->Perspective());
+    perspective_matrix.ApplyTransformOrigin(perspective_origin.X(),
+                                            perspective_origin.Y(), 0);
+
+    // TODO(chrishtr): This applies perspective before the transform. Why?

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

??? Weird.

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

This looks correct. See explanation above.

+    transform = perspective_matrix * transform;
+  }
+
+  // 5. Transform flattening.
+  transform_state.ApplyTransform(transform, accumulation);
+
+  // 6. Expansion for pixel snapping.
+  // Use enclosingBoundingBox because we cannot properly compute pixel
+  // snapping for painted elements within the transform since we don't know
+  // the desired subpixel accumulation at this point, and the transform may
+  // include a scale.
+  if (!preserve3D) {
+    transform_state.Flatten();
+    transform_state.SetQuad(
+        FloatQuad(transform_state.LastPlanarQuad().EnclosingBoundingBox()));
+  }
+
+  // 7. Container clip.
+  if (container_object->IsBox() && container_object != ancestor &&
+      container_object->HasClipRelatedProperty()) {
+    return ToLayoutBox(container_object)
+        ->ApplyBoxClips(transform_state, accumulation, visual_rect_flags);
+  }
+
+  return true;
+}
+
 bool LayoutBox::MapScrollingContentsRectToBoxSpace(
     TransformState& transform_state,
     TransformState::TransformAccumulation accumulation,
     VisualRectFlags visual_rect_flags) const {
   if (!HasClipRelatedProperty())
     return true;
 
   if (HasOverflowClip()) {
     LayoutSize offset = LayoutSize(-ScrolledContentOffset());
     transform_state.Move(offset, accumulation);
   }
 
+  return ApplyBoxClips(transform_state, accumulation, visual_rect_flags);
+}
+
+bool LayoutBox::ApplyBoxClips(
+    TransformState& transform_state,
+    TransformState::TransformAccumulation accumulation,
+    VisualRectFlags visual_rect_flags) const {
   // This won't work fully correctly for fixed-position elements, who should
   // receive CSS clip but for whom the current object is not in the containing
   // block chain.
   LayoutRect clip_rect = ClippingRect();
 
   transform_state.Flatten();
   LayoutRect rect(transform_state.LastPlanarQuad().EnclosingBoundingBox());
   bool does_intersect;
   if (visual_rect_flags & kEdgeInclusive) {
     does_intersect = rect.InclusiveIntersect(clip_rect);
@@ skipping 1229 matching lines @@
         ToLayoutInline(container)->OffsetForInFlowPositionedInline(*this));
   } else if (style_to_use.HasInFlowPosition() && Layer()) {
     // Apply the relative position offset when invalidating a rectangle. The
     // layer is translated, but the layout box isn't, so we need to do this to
     // get the right dirty rect.  Since this is called from
     // LayoutObject::setStyle, the relative position flag on the LayoutObject
     // has been cleared, so use the one on the style().
     container_offset.Move(Layer()->OffsetForInFlowPosition());
   }
 
-  bool preserve3d = container->Style()->Preserves3D();
-
-  TransformState::TransformAccumulation accumulation =
-      preserve3d ? TransformState::kAccumulateTransform
-                 : TransformState::kFlattenTransform;
-
   if (skip_info.FilterSkipped()) {
     InflateVisualRectForFilterUnderContainer(transform_state, *container,
                                              ancestor);
   }
 
-  // We are now in our parent container's coordinate space. Apply our transform
-  // to obtain a bounding box in the parent's coordinate space that encloses us.
-  if (ShouldUseTransformFromContainer(container)) {
-    TransformationMatrix t;
-    GetTransformFromContainer(container, ToLayoutSize(container_offset), t);
-    transform_state.ApplyTransform(t, accumulation);
-
-    // Use enclosingBoundingBox because we cannot properly compute pixel
-    // snapping for painted elements within the transform since we don't know
-    // the desired subpixel accumulation at this point, and the transform may
-    // include a scale.
-    if (!preserve3d) {
-      transform_state.Flatten();
-      transform_state.SetQuad(
-          FloatQuad(transform_state.LastPlanarQuad().EnclosingBoundingBox()));
-    }
-  } else {
-    transform_state.Move(ToLayoutSize(container_offset), accumulation);
-  }
-
-  // FIXME: We ignore the lightweight clipping rect that controls use, since if
-  // |o| is in mid-layout, its controlClipRect will be wrong. For overflow clip
-  // we use the values cached by the layer.
-  if (container->IsBox() && container != ancestor &&
-      !ToLayoutBox(container)->MapScrollingContentsRectToBoxSpace(
-          transform_state, accumulation, visual_rect_flags))
+  if (!MapVisualRectToContainer(container, container_offset, ancestor,
+                                visual_rect_flags, transform_state))
     return false;
 
   if (skip_info.AncestorSkipped()) {
+    bool preserve3D = container->Style()->Preserves3D();
+    TransformState::TransformAccumulation accumulation =
+        preserve3D ? TransformState::kAccumulateTransform
+                   : TransformState::kFlattenTransform;
+
     // If the ancestor is below the container, then we need to map the rect into
     // ancestor's coordinates.
     LayoutSize container_offset =
         ancestor->OffsetFromAncestorContainer(container);
     transform_state.Move(-container_offset, accumulation);
     // If the ancestor is fixed, then the rect is already in its coordinates so
     // doesn't need viewport-adjusting.
     if (ancestor->Style()->GetPosition() != EPosition::kFixed &&
         container->IsLayoutView() && position == EPosition::kFixed) {
       transform_state.Move(
@@ skipping 3337 matching lines @@
 void LayoutBox::MutableForPainting::
     SavePreviousContentBoxSizeAndLayoutOverflowRect() {
   auto& rare_data = GetLayoutBox().EnsureRareData();
   rare_data.has_previous_content_box_size_and_layout_overflow_rect_ = true;
   rare_data.previous_content_box_size_ = GetLayoutBox().ContentBoxRect().size();
   rare_data.previous_layout_overflow_rect_ =
       GetLayoutBox().LayoutOverflowRect();
 }
 
 }  // namespace blink