[UnifiedPDF] Can't click-drag the scrollbar

https://bugs.webkit.org/show_bug.cgi?id=271115
rdar://124785551

Reviewed by Abrar Rahman Protyasha.

For mouse interaction with the PDFPlugin's scrollbars to work, `EventHandler::enclosingScrollableArea()`
has to be able to find the plugin node's ScrollableArea. Add an easy way to get to the ScrollableArea
from RenderEmbeddedObject, which calls through the PluginView. Replace the odd code in `startKeyboardScrollAnimationOnPlugin()`
with this cleaner code.

Oddly that broke keyboard scrolling, which is fixed by implementing `scrollAnimatorEnabled()` in
PDFPluginBase to return true.

Also implement `PDFPluginBase::enclosingScrollableArea()`; this isn't called on macOS at this point, but
is implemented for completeness.

* Source/WebCore/page/EventHandler.cpp:
(WebCore::EventHandler::enclosingScrollableArea):
(WebCore::EventHandler::startKeyboardScrollAnimationOnPlugin):
* Source/WebCore/plugins/PluginViewBase.h:
(WebCore::PluginViewBase::scrollableArea const):
* Source/WebCore/rendering/RenderEmbeddedObject.cpp:
(WebCore::RenderEmbeddedObject::scrollableArea const):
(WebCore::RenderEmbeddedObject::usesAsyncScrolling const):
(WebCore::RenderEmbeddedObject::scrollingNodeID const):
(WebCore::RenderEmbeddedObject::willAttachScrollingNode):
(WebCore::RenderEmbeddedObject::didAttachScrollingNode):
* Source/WebCore/rendering/RenderEmbeddedObject.h:
* Source/WebKit/WebProcess/Plugins/PDF/PDFPluginBase.h:
* Source/WebKit/WebProcess/Plugins/PDF/PDFPluginBase.mm:
(WebKit::PDFPluginBase::enclosingScrollableArea const):
* Source/WebKit/WebProcess/Plugins/PluginView.cpp:
(WebKit::PluginView::scrollableArea const):
* Source/WebKit/WebProcess/Plugins/PluginView.h:

Canonical link: https://commits.webkit.org/276244@main

Source/WebCore/page/EventHandler.cpp

@@ -2009,6 +2009,11 @@ ScrollableArea* EventHandler::enclosingScrollableArea(Node* node)
                 return scrollableArea;
         }
 
+        if (RefPtr plugin = dynamicDowncast<RenderEmbeddedObject>(renderer)) {
+            if (auto* scrollableArea = plugin->scrollableArea())
+                return scrollableArea;
+        }
+
         auto* layer = renderer->enclosingLayer();
         if (!layer)
             return nullptr;
@@ -4614,17 +4619,16 @@ bool EventHandler::startKeyboardScrollAnimationOnRenderBoxAndItsAncestors(Scroll
     return false;
 }
 
-bool EventHandler::startKeyboardScrollAnimationOnPlugin(ScrollDirection direction, ScrollGranularity granularity, RenderEmbeddedObject& plugin, bool isKeyRepeat)
+bool EventHandler::startKeyboardScrollAnimationOnPlugin(ScrollDirection direction, ScrollGranularity granularity, RenderEmbeddedObject& pluginRenderer, bool isKeyRepeat)
 {
-    if (!plugin.usesAsyncScrolling())
-        return false;
-    ScrollingNodeID scroller = plugin.scrollingNodeID();
-    ScrollableArea* scrollableArea = m_frame->view()->scrollableAreaForScrollingNodeID(scroller);
+    auto* scrollableArea = pluginRenderer.scrollableArea();
     if (!scrollableArea)
         return false;
+
     auto* animator = scrollableArea->scrollAnimator().keyboardScrollingAnimator();
     if (!animator)
         return false;
+
     return beginKeyboardScrollGesture(animator, direction, granularity, isKeyRepeat);
 }
 

Source/WebCore/plugins/PluginViewBase.h

@@ -36,6 +36,7 @@ namespace WebCore {
 
 class Element;
 class GraphicsLayer;
+class ScrollableArea;
 class Scrollbar;
 class VoidCallback;
 
@@ -64,6 +65,7 @@ class PluginViewBase : public Widget {
     virtual bool shouldAllowNavigationFromDrags() const { return false; }
     virtual void willDetachRenderer() { }
 
+    virtual ScrollableArea* scrollableArea() const { return nullptr; }
     virtual bool usesAsyncScrolling() const { return false; }
     virtual ScrollingNodeID scrollingNodeID() const { return { }; }
     virtual void willAttachScrollingNode() { }

Source/WebCore/rendering/RenderEmbeddedObject.cpp

@@ -111,33 +111,42 @@ bool RenderEmbeddedObject::requiresAcceleratedCompositing() const
     return pluginViewBase->layerHostingStrategy() != PluginLayerHostingStrategy::None;
 }
 
+ScrollableArea* RenderEmbeddedObject::scrollableArea() const
+{
+    RefPtr pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
+    if (!pluginViewBase)
+        return nullptr;
+
+    return pluginViewBase->scrollableArea();
+}
+
 bool RenderEmbeddedObject::usesAsyncScrolling() const
 {
-    auto* pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
+    RefPtr pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
     if (!pluginViewBase)
         return false;
     return pluginViewBase->usesAsyncScrolling();
 }
 
 ScrollingNodeID RenderEmbeddedObject::scrollingNodeID() const
 {
-    auto* pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
+    RefPtr pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
     if (!pluginViewBase)
         return { };
     return pluginViewBase->scrollingNodeID();
 }
 
 void RenderEmbeddedObject::willAttachScrollingNode()
 {
-    auto* pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
+    RefPtr pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
     if (!pluginViewBase)
         return;
     pluginViewBase->willAttachScrollingNode();
 }
 
 void RenderEmbeddedObject::didAttachScrollingNode()
 {
-    auto* pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
+    RefPtr pluginViewBase = dynamicDowncast<PluginViewBase>(widget());
     if (!pluginViewBase)
         return;
     pluginViewBase->didAttachScrollingNode();

Source/WebCore/rendering/RenderEmbeddedObject.h

@@ -61,6 +61,7 @@ class RenderEmbeddedObject final : public RenderWidget {
 
     const String& pluginReplacementTextIfUnavailable() const { return m_unavailablePluginReplacementText; }
 
+    ScrollableArea* scrollableArea() const;
     bool usesAsyncScrolling() const;
     ScrollingNodeID scrollingNodeID() const;
     void willAttachScrollingNode();

Source/WebKit/WebProcess/Plugins/PDF/PDFPluginBase.h

@@ -297,6 +297,7 @@ class PDFPluginBase : public ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr<PDF
     // ScrollableArea functions.
     WebCore::IntRect scrollCornerRect() const final;
     WebCore::ScrollableArea* enclosingScrollableArea() const final;
+    bool scrollAnimatorEnabled() const final { return true; }
     bool isScrollableOrRubberbandable() final { return true; }
     bool hasScrollableOrRubberbandableAncestor() final { return true; }
     WebCore::IntRect scrollableAreaBoundingBox(bool* = nullptr) const final;

Source/WebKit/WebProcess/Plugins/PDF/PDFPluginBase.mm

@@ -59,6 +59,9 @@
 #import <WebCore/LocalizedStrings.h>
 #import <WebCore/MouseEvent.h>
 #import <WebCore/PluginDocument.h>
+#import <WebCore/RenderEmbeddedObject.h>
+#import <WebCore/RenderLayer.h>
+#import <WebCore/RenderLayerScrollableArea.h>
 #import <WebCore/ResourceResponse.h>
 #import <WebCore/ScrollAnimator.h>
 #import <WebCore/SharedBuffer.h>
@@ -663,8 +666,22 @@
 
 ScrollableArea* PDFPluginBase::enclosingScrollableArea() const
 {
-    // FIXME: Walk up the frame tree and look for a scrollable parent frame or RenderLayer.
-    return nullptr;
+    if (!m_element)
+        return nullptr;
+
+    RefPtr renderer = dynamicDowncast<RenderEmbeddedObject>(m_element->renderer());
+    if (!renderer)
+        return nullptr;
+
+    CheckedPtr layer = renderer->enclosingLayer();
+    if (!layer)
+        return nullptr;
+
+    CheckedPtr enclosingScrollableLayer = layer->enclosingScrollableLayer(IncludeSelfOrNot::ExcludeSelf, CrossFrameBoundaries::No);
+    if (!enclosingScrollableLayer)
+        return nullptr;
+
+    return enclosingScrollableLayer->scrollableArea();
 }
 
 IntRect PDFPluginBase::scrollableAreaBoundingBox(bool*) const

Source/WebKit/WebProcess/Plugins/PluginView.cpp

@@ -714,6 +714,14 @@ void PluginView::willDetachRenderer()
     protectedPlugin()->willDetachRenderer();
 }
 
+ScrollableArea* PluginView::scrollableArea() const
+{
+    if (!m_isInitialized)
+        return nullptr;
+
+    return m_plugin.ptr();
+}
+
 bool PluginView::usesAsyncScrolling() const
 {
     if (!m_isInitialized)
@@ -722,7 +730,6 @@ bool PluginView::usesAsyncScrolling() const
     return protectedPlugin()->usesAsyncScrolling();
 }
 
-
 ScrollingNodeID PluginView::scrollingNodeID() const
 {
     if (!m_isInitialized)

Source/WebKit/WebProcess/Plugins/PluginView.h

@@ -159,6 +159,7 @@ class PluginView final : public WebCore::PluginViewBase {
     bool shouldAllowNavigationFromDrags() const final;
     void willDetachRenderer() final;
 
+    WebCore::ScrollableArea* scrollableArea() const final;
     bool usesAsyncScrolling() const final;
     WebCore::ScrollingNodeID scrollingNodeID() const final;
     void willAttachScrollingNode() final;