Compute effective touch action in StyleAdjuster.

third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp

Index: third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp b/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
index d561f3f6cb0dcfc2b8bc7f28686600aa54c3415c..4a995a3aef75e94cee445867174411d969eb5ada 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
@@ -35,6 +35,7 @@
 #include "core/dom/ContainerNode.h"
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
+#include "core/dom/NodeComputedStyle.h"
 #include "core/frame/LocalFrameView.h"
 #include "core/frame/Settings.h"
 #include "core/frame/UseCounter.h"
@@ -44,6 +45,7 @@
 #include "core/html/HTMLPlugInElement.h"
 #include "core/html/HTMLTableCellElement.h"
 #include "core/html/HTMLTextAreaElement.h"
+#include "core/layout/LayoutObject.h"
 #include "core/layout/LayoutTheme.h"
 #include "core/style/ComputedStyle.h"
 #include "core/style/ComputedStyleConstants.h"
@@ -368,6 +370,52 @@ static void AdjustStyleForDisplay(ComputedStyle& style,
   }
 }
 
+static void AdjustEffectiveTouchAction(ComputedStyle& style,
+                                       const ComputedStyle& parent_style,
+                                       Element* element) {
+  TouchAction action = parent_style.GetEffectiveTouchAction();
+
+  bool is_svg_root = element && element->IsSVGElement() &&
+                     isSVGSVGElement(*element) && element->parentNode() &&
+                     !element->parentNode()->IsSVGElement();
+  bool is_non_replaced_inline_elements =
+      style.IsDisplayInlineType() &&
+      !(style.IsDisplayReplacedType() || is_svg_root ||
+        isHTMLImageElement(element));
+  bool is_table_row_or_column = style.IsDisplayTableRowOrColumnType();
+
+  // According to W3C specs, touch actions are only supported by elements that
+  // support both the CSS width and height properties.
+  // See https://www.w3.org/TR/pointerevents/#the-touch-action-css-property.
+  if (is_non_replaced_inline_elements || is_table_row_or_column) {
+    style.SetEffectiveTouchAction(action);
+    return;
+  }
+
+  // The effective touch action is the intersection of the touch-action values
+  // of the current element and all of its ancestors up to the one that
+  // implements the gesture. Since panning is implemented by the scroller it is
+  // re-enabled for scrolling elements.
+  if (style.ScrollsOverflow())
+    action |= TouchAction::kTouchActionPan;
+
+  // The panning-restricted cancellation should also apply to iframes, so we
+  // allow (panning & local touch action) on the first descendant element of a

[flackr, 2017/06/08 19:35:21]

local touch action? Is this the owning frame node's action?

Will this function be called on the child frame if the parent owner's effective
touch action changes? It seems like it wouldn't know to since the parent_style
didn't change. I think you might need to check if element is a
HTMLFrameOwnerElement and then set the effective touch action on its
contentDocument().

[sunxd, 2017/06/09 21:00:35]

Yeah that's a good point, I have verified that a change of iframe's touch-action
style cannot propagate to the document contents. I tried setting the effective
touch actions of the contentDocument but it didn't trigger a recalcStyle of the
internal element. Is there any way to manually trigger that?

+  // iframe element.
+  if (element && element == element->GetDocument().documentElement() &&
+      element->GetDocument().LocalOwner()) {
+    const ComputedStyle* frame_style =
+        element->GetDocument().LocalOwner()->GetComputedStyle();
+    if (frame_style) {
+      action =
+          frame_style->GetEffectiveTouchAction() | TouchAction::kTouchActionPan;
+    }
+  }
+
+  // Apply the adjusted parent effective touch actions.
+  style.SetEffectiveTouchAction(style.GetTouchAction() & action);
+}
+
 void StyleAdjuster::AdjustComputedStyle(
     ComputedStyle& style,
     const ComputedStyle& parent_style,
@@ -498,6 +546,7 @@ void StyleAdjuster::AdjustComputedStyle(
     if (parent_style.JustifyItemsPositionType() == kLegacyPosition)
       style.SetJustifyItems(parent_style.JustifyItems());
   }
-}
 
+  AdjustEffectiveTouchAction(style, parent_style, element);
+}
 }  // namespace blink