third_party/WebKit/Source/platform/graphics/paint/GeometryMapper.cpp - chromium/src.git - Git at Google

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "platform/graphics/paint/GeometryMapper.h"

 #include "platform/geometry/LayoutRect.h"
 #include "platform/runtime_enabled_features.h"

 namespace blink {

 const TransformationMatrix& GeometryMapper::SourceToDestinationProjection(
     const TransformPaintPropertyNode* source,
     const TransformPaintPropertyNode* destination) {
   DCHECK(source && destination);
   bool success = false;
   const auto& result =
       SourceToDestinationProjectionInternal(source, destination, success);
   DCHECK(success);
   return result;
 }

 // Returns flatten(destination_to_screen)^-1 * flatten(source_to_screen)
 //
 // In case that source and destination are coplanar in tree hierarchy [1],
 // computes destination_to_plane_root ^ -1 * source_to_plane_root.
 // It can be proved that [2] the result will be the same (except numerical
 // errors) when the plane root has invertible screen projection, and this
 // offers fallback definition when plane root is singular. For example:
 // <div style="transform:rotateY(90deg); overflow:scroll;">
 //   <div id="A" style="opacity:0.5;">
 //     <div id="B" style="position:absolute;"></div>
 //   </div>
 // </div>
 // Both A and B have non-invertible screen projection, nevertheless it is
 // useful to define projection between A and B. Say, the transform may be
 // animated in compositor thus become visible.
 // As SPv1 treats 3D transforms as compositing trigger, that implies mappings
 // within the same compositing layer can only contain 2D transforms, thus
 // intra-composited-layer queries are guaranteed to be handled correctly.
 //
 // [1] As defined by that all local transforms between source and some common
 //     ancestor 'plane root' and all local transforms between the destination
 //     and the plane root being flat.
 // [2] destination_to_screen = plane_root_to_screen * destination_to_plane_root
 //     source_to_screen = plane_root_to_screen * source_to_plane_root
 //     output = flatten(destination_to_screen)^-1 * flatten(source_to_screen)
 //     = flatten(plane_root_to_screen * destination_to_plane_root)^-1 *
 //       flatten(plane_root_to_screen * source_to_plane_root)
 //     Because both destination_to_plane_root and source_to_plane_root are
 //     already flat,
 //     = flatten(plane_root_to_screen * flatten(destination_to_plane_root))^-1 *
 //       flatten(plane_root_to_screen * flatten(source_to_plane_root))
 //     By flatten lemma [3] flatten(A * flatten(B)) = flatten(A) * flatten(B),
 //     = flatten(destination_to_plane_root)^-1 *
 //       flatten(plane_root_to_screen)^-1 *
 //       flatten(plane_root_to_screen) * flatten(source_to_plane_root)
 //     If flatten(plane_root_to_screen) is invertible, they cancel out:
 //     = flatten(destination_to_plane_root)^-1 * flatten(source_to_plane_root)
 //     = destination_to_plane_root^-1 * source_to_plane_root
 // [3] Flatten lemma: https://goo.gl/DNKyOc
 const TransformationMatrix&
 GeometryMapper::SourceToDestinationProjectionInternal(
     const TransformPaintPropertyNode* source,
     const TransformPaintPropertyNode* destination,
     bool& success) {
   DCHECK(source && destination);
   DEFINE_STATIC_LOCAL(TransformationMatrix, identity, (TransformationMatrix()));
   DEFINE_STATIC_LOCAL(TransformationMatrix, temp, (TransformationMatrix()));

   if (source == destination) {
     success = true;
     return identity;
   }

   const GeometryMapperTransformCache& source_cache =
       source->GetTransformCache();
   const GeometryMapperTransformCache& destination_cache =
       destination->GetTransformCache();

   // Case 1: Check if source and destination are known to be coplanar.
   // Even if destination may have invertible screen projection,
   // this formula is likely to be numerically more stable.
   if (source_cache.plane_root() == destination_cache.plane_root()) {
     success = true;
     if (source == destination_cache.plane_root())
       return destination_cache.from_plane_root();
     if (destination == source_cache.plane_root())
       return source_cache.to_plane_root();
     temp = destination_cache.from_plane_root();
     temp.Multiply(source_cache.to_plane_root());
     return temp;
   }

   // Case 2: Check if we can fallback to the canonical definition of
   // flatten(destination_to_screen)^-1 * flatten(source_to_screen)
   // If flatten(destination_to_screen)^-1 is invalid, we are out of luck.
   if (!destination_cache.projection_from_screen_is_valid()) {
     success = false;
     return identity;
   }

   // Case 3: Compute:
   // flatten(destination_to_screen)^-1 * flatten(source_to_screen)
   const auto* root = TransformPaintPropertyNode::Root();
   success = true;
   if (source == root)
     return destination_cache.projection_from_screen();
   if (destination == root) {
     temp = source_cache.to_screen();
   } else {
     temp = destination_cache.projection_from_screen();
     temp.Multiply(source_cache.to_screen());
   }
   temp.FlattenTo2d();
   return temp;
 }

 void GeometryMapper::SourceToDestinationRect(
     const TransformPaintPropertyNode* source_transform_node,
     const TransformPaintPropertyNode* destination_transform_node,
     FloatRect& mapping_rect) {
   bool success = false;
   const TransformationMatrix& source_to_destination =
       SourceToDestinationProjectionInternal(
           source_transform_node, destination_transform_node, success);
   mapping_rect =
       success ? source_to_destination.MapRect(mapping_rect) : FloatRect();
 }

 void GeometryMapper::LocalToAncestorVisualRect(
     const PropertyTreeState& local_state,
     const PropertyTreeState& ancestor_state,
     FloatClipRect& mapping_rect,
     OverlayScrollbarClipBehavior clip_behavior) {
   bool success = false;
   LocalToAncestorVisualRectInternal(local_state, ancestor_state, mapping_rect,
                                     clip_behavior, success);
   DCHECK(success);
 }

 void GeometryMapper::LocalToAncestorVisualRectInternal(
     const PropertyTreeState& local_state,
     const PropertyTreeState& ancestor_state,
     FloatClipRect& rect_to_map,
     OverlayScrollbarClipBehavior clip_behavior,
     bool& success) {
   if (local_state == ancestor_state) {
     success = true;
     return;
   }

   if (local_state.Effect() != ancestor_state.Effect()) {
     SlowLocalToAncestorVisualRectWithEffects(
         local_state, ancestor_state, rect_to_map, clip_behavior, success);
     return;
   }

   const auto& transform_matrix = SourceToDestinationProjectionInternal(
       local_state.Transform(), ancestor_state.Transform(), success);
   if (!success) {
     // A failure implies either source-to-plane or destination-to-plane being
     // singular. A notable example of singular source-to-plane from valid CSS:
     // <div id="plane" style="transform:rotateY(180deg)">
     //   <div style="overflow:overflow">
     //     <div id="ancestor" style="opacity:0.5;">
     //       <div id="local" style="position:absolute; transform:scaleX(0);">
     //       </div>
     //     </div>
     //   </div>
     // </div>
     // Either way, the element won't be renderable thus returning empty rect.
     success = true;
     rect_to_map = FloatClipRect(FloatRect());
     return;
   }
   rect_to_map.Map(transform_matrix);

   FloatClipRect clip_rect = LocalToAncestorClipRectInternal(
       local_state.Clip(), ancestor_state.Clip(), ancestor_state.Transform(),
       clip_behavior, success);
   if (success) {
     // This is where we propagate the roundedness and tightness of |clip_rect|
     // to |rect_to_map|.
     rect_to_map.Intersect(clip_rect);
     return;
   }

   if (!RuntimeEnabledFeatures::SlimmingPaintV2Enabled()) {
     // On SPv1* we may fail when the paint invalidation container creates an
     // overflow clip (in ancestor_state) which is not in localState of an
     // out-of-flow positioned descendant. See crbug.com/513108 and layout test
     // compositing/overflow/handle-non-ancestor-clip-parent.html (run with
     // --enable-prefer-compositing-to-lcd-text) for details.
     // Ignore it for SPv1* for now.
     success = true;
     rect_to_map.ClearIsTight();
   }
 }

 void GeometryMapper::SlowLocalToAncestorVisualRectWithEffects(
     const PropertyTreeState& local_state,
     const PropertyTreeState& ancestor_state,
     FloatClipRect& mapping_rect,
     OverlayScrollbarClipBehavior clip_behavior,
     bool& success) {
   PropertyTreeState last_transform_and_clip_state(local_state.Transform(),
                                                   local_state.Clip(), nullptr);

   for (const auto* effect = local_state.Effect();
        effect && effect != ancestor_state.Effect(); effect = effect->Parent()) {
     if (!effect->HasFilterThatMovesPixels())
       continue;

     DCHECK(effect->OutputClip());
     PropertyTreeState transform_and_clip_state(effect->LocalTransformSpace(),
                                                effect->OutputClip(), nullptr);
     LocalToAncestorVisualRectInternal(last_transform_and_clip_state,
                                       transform_and_clip_state, mapping_rect,
                                       clip_behavior, success);
     if (!success) {
       success = true;
       mapping_rect = FloatClipRect(FloatRect());
       return;
     }

     mapping_rect = FloatClipRect(effect->MapRect(mapping_rect.Rect()));
     last_transform_and_clip_state = transform_and_clip_state;
   }

   PropertyTreeState final_transform_and_clip_state(
       ancestor_state.Transform(), ancestor_state.Clip(), nullptr);
   LocalToAncestorVisualRectInternal(last_transform_and_clip_state,
                                     final_transform_and_clip_state,
                                     mapping_rect, clip_behavior, success);

   // Many effects (e.g. filters, clip-paths) can make a clip rect not tight.
   mapping_rect.ClearIsTight();
 }

 FloatClipRect GeometryMapper::LocalToAncestorClipRect(
     const PropertyTreeState& local_state,
     const PropertyTreeState& ancestor_state,
     OverlayScrollbarClipBehavior clip_behavior) {
   if (local_state.Clip() == ancestor_state.Clip())
     return FloatClipRect();

   bool success = false;
   auto result = LocalToAncestorClipRectInternal(
       local_state.Clip(), ancestor_state.Clip(), ancestor_state.Transform(),
       clip_behavior, success);
   DCHECK(success);
   return result;
 }

 FloatClipRect GeometryMapper::LocalToAncestorClipRectInternal(
     const ClipPaintPropertyNode* descendant,
     const ClipPaintPropertyNode* ancestor_clip,
     const TransformPaintPropertyNode* ancestor_transform,
     OverlayScrollbarClipBehavior clip_behavior,
     bool& success) {
   FloatClipRect clip;
   if (descendant == ancestor_clip) {
     success = true;
     return FloatClipRect();
   }

   const ClipPaintPropertyNode* clip_node = descendant;
   Vector<const ClipPaintPropertyNode*> intermediate_nodes;

   GeometryMapperClipCache::ClipAndTransform clip_and_transform(
       ancestor_clip, ancestor_transform, clip_behavior);
   // Iterate over the path from localState.clip to ancestor_state.clip. Stop if
   // we've found a memoized (precomputed) clip for any particular node.
   while (clip_node && clip_node != ancestor_clip) {
     if (const FloatClipRect* cached_clip =
             clip_node->GetClipCache().GetCachedClip(clip_and_transform)) {
       clip = *cached_clip;
       break;
     }

     intermediate_nodes.push_back(clip_node);
     clip_node = clip_node->Parent();
   }
   if (!clip_node) {
     success = false;
     if (!RuntimeEnabledFeatures::SlimmingPaintV2Enabled()) {
       // On SPv1 we may fail when the paint invalidation container creates an
       // overflow clip (in ancestor_state) which is not in localState of an
       // out-of-flow positioned descendant. See crbug.com/513108 and layout
       // test compositing/overflow/handle-non-ancestor-clip-parent.html (run
       // with --enable-prefer-compositing-to-lcd-text) for details.
       // Ignore it for SPv1 for now.
       success = true;
     }
     FloatClipRect loose_infinite;
     loose_infinite.ClearIsTight();
     return loose_infinite;
   }

   // Iterate down from the top intermediate node found in the previous loop,
   // computing and memoizing clip rects as we go.
   for (auto it = intermediate_nodes.rbegin(); it != intermediate_nodes.rend();
        ++it) {
     const TransformationMatrix& transform_matrix =
         SourceToDestinationProjectionInternal((*it)->LocalTransformSpace(),
                                               ancestor_transform, success);
     if (!success) {
       success = true;
       return FloatClipRect(FloatRect());
     }

     // This is where we generate the roundedness and tightness of clip rect
     // from clip and transform properties, and propagate them to |clip|.
     FloatClipRect mapped_rect(clip_behavior ==
                                       kExcludeOverlayScrollbarSizeForHitTesting
                                   ? (*it)->ClipRectExcludingOverlayScrollbars()
                                   : (*it)->ClipRect());
     mapped_rect.Map(transform_matrix);
     clip.Intersect(mapped_rect);

     (*it)->GetClipCache().SetCachedClip(clip_and_transform, clip);
   }

   DCHECK(*descendant->GetClipCache().GetCachedClip(clip_and_transform) == clip);
   success = true;
   return clip;
 }

 void GeometryMapper::ClearCache() {
   GeometryMapperTransformCache::ClearCache();
   GeometryMapperClipCache::ClearCache();
 }

 }  // namespace blink
	// Copyright 2016 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "platform/graphics/paint/GeometryMapper.h"

	#include "platform/geometry/LayoutRect.h"
	#include "platform/runtime_enabled_features.h"

	namespace blink {

	const TransformationMatrix& GeometryMapper::SourceToDestinationProjection(
	const TransformPaintPropertyNode* source,
	const TransformPaintPropertyNode* destination) {
	DCHECK(source && destination);
	bool success = false;
	const auto& result =
	SourceToDestinationProjectionInternal(source, destination, success);
	DCHECK(success);
	return result;
	}

	// Returns flatten(destination_to_screen)^-1 * flatten(source_to_screen)
	//
	// In case that source and destination are coplanar in tree hierarchy [1],
	// computes destination_to_plane_root ^ -1 * source_to_plane_root.
	// It can be proved that [2] the result will be the same (except numerical
	// errors) when the plane root has invertible screen projection, and this
	// offers fallback definition when plane root is singular. For example:
	// <div style="transform:rotateY(90deg); overflow:scroll;">
	// <div id="A" style="opacity:0.5;">
	// <div id="B" style="position:absolute;"></div>
	// </div>
	// </div>
	// Both A and B have non-invertible screen projection, nevertheless it is
	// useful to define projection between A and B. Say, the transform may be
	// animated in compositor thus become visible.
	// As SPv1 treats 3D transforms as compositing trigger, that implies mappings
	// within the same compositing layer can only contain 2D transforms, thus
	// intra-composited-layer queries are guaranteed to be handled correctly.
	//
	// [1] As defined by that all local transforms between source and some common
	// ancestor 'plane root' and all local transforms between the destination
	// and the plane root being flat.
	// [2] destination_to_screen = plane_root_to_screen * destination_to_plane_root
	// source_to_screen = plane_root_to_screen * source_to_plane_root
	// output = flatten(destination_to_screen)^-1 * flatten(source_to_screen)
	// = flatten(plane_root_to_screen * destination_to_plane_root)^-1 *
	// flatten(plane_root_to_screen * source_to_plane_root)
	// Because both destination_to_plane_root and source_to_plane_root are
	// already flat,
	// = flatten(plane_root_to_screen * flatten(destination_to_plane_root))^-1 *
	// flatten(plane_root_to_screen * flatten(source_to_plane_root))
	// By flatten lemma [3] flatten(A * flatten(B)) = flatten(A) * flatten(B),
	// = flatten(destination_to_plane_root)^-1 *
	// flatten(plane_root_to_screen)^-1 *
	// flatten(plane_root_to_screen) * flatten(source_to_plane_root)
	// If flatten(plane_root_to_screen) is invertible, they cancel out:
	// = flatten(destination_to_plane_root)^-1 * flatten(source_to_plane_root)
	// = destination_to_plane_root^-1 * source_to_plane_root
	// [3] Flatten lemma: https://goo.gl/DNKyOc
	const TransformationMatrix&
	GeometryMapper::SourceToDestinationProjectionInternal(
	const TransformPaintPropertyNode* source,
	const TransformPaintPropertyNode* destination,
	bool& success) {
	DCHECK(source && destination);
	DEFINE_STATIC_LOCAL(TransformationMatrix, identity, (TransformationMatrix()));
	DEFINE_STATIC_LOCAL(TransformationMatrix, temp, (TransformationMatrix()));

	if (source == destination) {
	success = true;
	return identity;
	}

	const GeometryMapperTransformCache& source_cache =
	source->GetTransformCache();
	const GeometryMapperTransformCache& destination_cache =
	destination->GetTransformCache();

	// Case 1: Check if source and destination are known to be coplanar.
	// Even if destination may have invertible screen projection,
	// this formula is likely to be numerically more stable.
	if (source_cache.plane_root() == destination_cache.plane_root()) {
	success = true;
	if (source == destination_cache.plane_root())
	return destination_cache.from_plane_root();
	if (destination == source_cache.plane_root())
	return source_cache.to_plane_root();
	temp = destination_cache.from_plane_root();
	temp.Multiply(source_cache.to_plane_root());
	return temp;
	}

	// Case 2: Check if we can fallback to the canonical definition of
	// flatten(destination_to_screen)^-1 * flatten(source_to_screen)
	// If flatten(destination_to_screen)^-1 is invalid, we are out of luck.
	if (!destination_cache.projection_from_screen_is_valid()) {
	success = false;
	return identity;
	}

	// Case 3: Compute:
	// flatten(destination_to_screen)^-1 * flatten(source_to_screen)
	const auto* root = TransformPaintPropertyNode::Root();
	success = true;
	if (source == root)
	return destination_cache.projection_from_screen();
	if (destination == root) {
	temp = source_cache.to_screen();
	} else {
	temp = destination_cache.projection_from_screen();
	temp.Multiply(source_cache.to_screen());
	}
	temp.FlattenTo2d();
	return temp;
	}

	void GeometryMapper::SourceToDestinationRect(
	const TransformPaintPropertyNode* source_transform_node,
	const TransformPaintPropertyNode* destination_transform_node,
	FloatRect& mapping_rect) {
	bool success = false;
	const TransformationMatrix& source_to_destination =
	SourceToDestinationProjectionInternal(
	source_transform_node, destination_transform_node, success);
	mapping_rect =
	success ? source_to_destination.MapRect(mapping_rect) : FloatRect();
	}

	void GeometryMapper::LocalToAncestorVisualRect(
	const PropertyTreeState& local_state,
	const PropertyTreeState& ancestor_state,
	FloatClipRect& mapping_rect,
	OverlayScrollbarClipBehavior clip_behavior) {
	bool success = false;
	LocalToAncestorVisualRectInternal(local_state, ancestor_state, mapping_rect,
	clip_behavior, success);
	DCHECK(success);
	}

	void GeometryMapper::LocalToAncestorVisualRectInternal(
	const PropertyTreeState& local_state,
	const PropertyTreeState& ancestor_state,
	FloatClipRect& rect_to_map,
	OverlayScrollbarClipBehavior clip_behavior,
	bool& success) {
	if (local_state == ancestor_state) {
	success = true;
	return;
	}

	if (local_state.Effect() != ancestor_state.Effect()) {
	SlowLocalToAncestorVisualRectWithEffects(
	local_state, ancestor_state, rect_to_map, clip_behavior, success);
	return;
	}

	const auto& transform_matrix = SourceToDestinationProjectionInternal(
	local_state.Transform(), ancestor_state.Transform(), success);
	if (!success) {
	// A failure implies either source-to-plane or destination-to-plane being
	// singular. A notable example of singular source-to-plane from valid CSS:
	// <div id="plane" style="transform:rotateY(180deg)">
	// <div style="overflow:overflow">
	// <div id="ancestor" style="opacity:0.5;">
	// <div id="local" style="position:absolute; transform:scaleX(0);">
	// </div>
	// </div>
	// </div>
	// </div>
	// Either way, the element won't be renderable thus returning empty rect.
	success = true;
	rect_to_map = FloatClipRect(FloatRect());
	return;
	}
	rect_to_map.Map(transform_matrix);

	FloatClipRect clip_rect = LocalToAncestorClipRectInternal(
	local_state.Clip(), ancestor_state.Clip(), ancestor_state.Transform(),
	clip_behavior, success);
	if (success) {
	// This is where we propagate the roundedness and tightness of \|clip_rect\|
	// to \|rect_to_map\|.
	rect_to_map.Intersect(clip_rect);
	return;
	}

	if (!RuntimeEnabledFeatures::SlimmingPaintV2Enabled()) {
	// On SPv1* we may fail when the paint invalidation container creates an
	// overflow clip (in ancestor_state) which is not in localState of an
	// out-of-flow positioned descendant. See crbug.com/513108 and layout test
	// compositing/overflow/handle-non-ancestor-clip-parent.html (run with
	// --enable-prefer-compositing-to-lcd-text) for details.
	// Ignore it for SPv1* for now.
	success = true;
	rect_to_map.ClearIsTight();
	}
	}

	void GeometryMapper::SlowLocalToAncestorVisualRectWithEffects(
	const PropertyTreeState& local_state,
	const PropertyTreeState& ancestor_state,
	FloatClipRect& mapping_rect,
	OverlayScrollbarClipBehavior clip_behavior,
	bool& success) {
	PropertyTreeState last_transform_and_clip_state(local_state.Transform(),
	local_state.Clip(), nullptr);

	for (const auto* effect = local_state.Effect();
	effect && effect != ancestor_state.Effect(); effect = effect->Parent()) {
	if (!effect->HasFilterThatMovesPixels())
	continue;

	DCHECK(effect->OutputClip());
	PropertyTreeState transform_and_clip_state(effect->LocalTransformSpace(),
	effect->OutputClip(), nullptr);
	LocalToAncestorVisualRectInternal(last_transform_and_clip_state,
	transform_and_clip_state, mapping_rect,
	clip_behavior, success);
	if (!success) {
	success = true;
	mapping_rect = FloatClipRect(FloatRect());
	return;
	}

	mapping_rect = FloatClipRect(effect->MapRect(mapping_rect.Rect()));
	last_transform_and_clip_state = transform_and_clip_state;
	}

	PropertyTreeState final_transform_and_clip_state(
	ancestor_state.Transform(), ancestor_state.Clip(), nullptr);
	LocalToAncestorVisualRectInternal(last_transform_and_clip_state,
	final_transform_and_clip_state,
	mapping_rect, clip_behavior, success);

	// Many effects (e.g. filters, clip-paths) can make a clip rect not tight.
	mapping_rect.ClearIsTight();
	}

	FloatClipRect GeometryMapper::LocalToAncestorClipRect(
	const PropertyTreeState& local_state,
	const PropertyTreeState& ancestor_state,
	OverlayScrollbarClipBehavior clip_behavior) {
	if (local_state.Clip() == ancestor_state.Clip())
	return FloatClipRect();

	bool success = false;
	auto result = LocalToAncestorClipRectInternal(
	local_state.Clip(), ancestor_state.Clip(), ancestor_state.Transform(),
	clip_behavior, success);
	DCHECK(success);
	return result;
	}

	FloatClipRect GeometryMapper::LocalToAncestorClipRectInternal(
	const ClipPaintPropertyNode* descendant,
	const ClipPaintPropertyNode* ancestor_clip,
	const TransformPaintPropertyNode* ancestor_transform,
	OverlayScrollbarClipBehavior clip_behavior,
	bool& success) {
	FloatClipRect clip;
	if (descendant == ancestor_clip) {
	success = true;
	return FloatClipRect();
	}

	const ClipPaintPropertyNode* clip_node = descendant;
	Vector<const ClipPaintPropertyNode*> intermediate_nodes;

	GeometryMapperClipCache::ClipAndTransform clip_and_transform(
	ancestor_clip, ancestor_transform, clip_behavior);
	// Iterate over the path from localState.clip to ancestor_state.clip. Stop if
	// we've found a memoized (precomputed) clip for any particular node.
	while (clip_node && clip_node != ancestor_clip) {
	if (const FloatClipRect* cached_clip =
	clip_node->GetClipCache().GetCachedClip(clip_and_transform)) {
	clip = *cached_clip;
	break;
	}

	intermediate_nodes.push_back(clip_node);
	clip_node = clip_node->Parent();
	}
	if (!clip_node) {
	success = false;
	if (!RuntimeEnabledFeatures::SlimmingPaintV2Enabled()) {
	// On SPv1 we may fail when the paint invalidation container creates an
	// overflow clip (in ancestor_state) which is not in localState of an
	// out-of-flow positioned descendant. See crbug.com/513108 and layout
	// test compositing/overflow/handle-non-ancestor-clip-parent.html (run
	// with --enable-prefer-compositing-to-lcd-text) for details.
	// Ignore it for SPv1 for now.
	success = true;
	}
	FloatClipRect loose_infinite;
	loose_infinite.ClearIsTight();
	return loose_infinite;
	}

	// Iterate down from the top intermediate node found in the previous loop,
	// computing and memoizing clip rects as we go.
	for (auto it = intermediate_nodes.rbegin(); it != intermediate_nodes.rend();
	++it) {
	const TransformationMatrix& transform_matrix =
	SourceToDestinationProjectionInternal((*it)->LocalTransformSpace(),
	ancestor_transform, success);
	if (!success) {
	success = true;
	return FloatClipRect(FloatRect());
	}

	// This is where we generate the roundedness and tightness of clip rect
	// from clip and transform properties, and propagate them to \|clip\|.
	FloatClipRect mapped_rect(clip_behavior ==
	kExcludeOverlayScrollbarSizeForHitTesting
	? (*it)->ClipRectExcludingOverlayScrollbars()
	: (*it)->ClipRect());
	mapped_rect.Map(transform_matrix);
	clip.Intersect(mapped_rect);

	(*it)->GetClipCache().SetCachedClip(clip_and_transform, clip);
	}

	DCHECK(*descendant->GetClipCache().GetCachedClip(clip_and_transform) == clip);
	success = true;
	return clip;
	}

	void GeometryMapper::ClearCache() {
	GeometryMapperTransformCache::ClearCache();
	GeometryMapperClipCache::ClearCache();
	}

	} // namespace blink