Scrolling with page granularity using keyboard smooth scrolling doesn…

…'t account for fixed content

https://bugs.webkit.org/show_bug.cgi?id=245746
rdar://100469555

Reviewed by Tim Horton.

When keyboard smooth scrolling is enabled, `KeyboardScrollingAnimator::scrollDistance`
is used, which is analagous to `ScrollableArea::scroll`. However, while the
latter accounts for page's having fixed content when scrolling with page
granularity, the former never does.

This PR fixes this by including the same logic that `ScrollableArea::scroll` has
to adjust the scroll step into `KeyboardScrollingAnimator::scrollDistance`.

* LayoutTests/scrollbars/scrolling-backward-by-page-accounting-bottom-fixed-elements-on-keyboard-spacebar.html:
* Source/WebCore/platform/KeyboardScrollingAnimator.cpp:
(WebCore::KeyboardScrollingAnimator::scrollDistance const):
* Source/WebCore/platform/ScrollableArea.h:

Canonical link: https://commits.webkit.org/254963@main

Source/WebCore/platform/KeyboardScrollingAnimator.cpp

@@ -27,6 +27,7 @@
 #include "KeyboardScrollingAnimator.h"
 
 #include "EventNames.h"
+#include "FrameView.h"
 #include "PlatformKeyboardEvent.h"
 #include "ScrollTypes.h"
 #include "ScrollableArea.h"
@@ -226,20 +227,30 @@ void KeyboardScrollingAnimator::updateKeyboardScrollPosition(MonotonicTime curre
 float KeyboardScrollingAnimator::scrollDistance(ScrollDirection direction, ScrollGranularity granularity) const
 {
     auto scrollbar = m_scrollAnimator.scrollableArea().scrollbarForDirection(direction);
-    if (scrollbar) {
-        switch (granularity) {
-        case ScrollGranularity::Line:
-            return scrollbar->lineStep();
-        case ScrollGranularity::Page:
-            return scrollbar->pageStep();
-        case ScrollGranularity::Document:
-            return scrollbar->totalSize();
-        case ScrollGranularity::Pixel:
-            return scrollbar->pixelStep();
-        }
+    if (!scrollbar)
+        return false;
+
+    float step = 0;
+    switch (granularity) {
+    case ScrollGranularity::Line:
+        step = scrollbar->lineStep();
+        break;
+    case ScrollGranularity::Page:
+        step = scrollbar->pageStep();
+        break;
+    case ScrollGranularity::Document:
+        step = scrollbar->totalSize();
+        break;
+    case ScrollGranularity::Pixel:
+        step = scrollbar->pixelStep();
+        break;
     }
 
-    return 0;
+    auto axis = axisFromDirection(direction);
+    if (granularity == ScrollGranularity::Page && axis == ScrollEventAxis::Vertical)
+        step = m_scrollAnimator.scrollableArea().adjustVerticalPageScrollStepForFixedContent(step);
+
+    return step;
 }
 
 std::optional<KeyboardScroll> KeyboardScrollingAnimator::makeKeyboardScroll(ScrollDirection direction, ScrollGranularity granularity) const

Source/WebCore/platform/ScrollableArea.h

@@ -386,6 +386,7 @@ class ScrollableArea : public CanMakeWeakPtr<ScrollableArea> {
     bool overscrollBehaviorAllowsRubberBand() const { return horizontalOverscrollBehavior() != OverscrollBehavior::None || verticalOverscrollBehavior() != OverscrollBehavior::None; }
     bool shouldBlockScrollPropagation(const FloatSize&) const;
     FloatSize deltaForPropagation(const FloatSize&) const;
+    WEBCORE_EXPORT virtual float adjustVerticalPageScrollStepForFixedContent(float step);
 
 protected:
     WEBCORE_EXPORT ScrollableArea();
@@ -394,7 +395,6 @@ class ScrollableArea : public CanMakeWeakPtr<ScrollableArea> {
     void setScrollOrigin(const IntPoint&);
     void resetScrollOriginChanged() { m_scrollOriginChanged = false; }
 
-    WEBCORE_EXPORT virtual float adjustVerticalPageScrollStepForFixedContent(float step);
     virtual void invalidateScrollbarRect(Scrollbar&, const IntRect&) = 0;
     virtual void invalidateScrollCornerRect(const IntRect&) = 0;
 

Source/WebKit/UIProcess/ios/WKKeyboardScrollingAnimator.mm

@@ -259,6 +259,7 @@ - (void)invalidate
     }();
 
     // FIXME (227461): Replace with call to WebCore::KeyboardScroll constructor.
+    // FIXME (245749): Use `ScrollableArea::adjustVerticalPageScrollStepForFixedContent` to account for fixed content
 
     CGFloat scrollDistance = [_scrollable distanceForIncrement:increment inDirection:direction];