Bug 1617427 - Refactor to extract helper method; no functional changes. r=tnikkel

Differential Revision: https://phabricator.services.mozilla.com/D66420

--HG--
extra : moz-landing-system : lando

layout/generic/nsGfxScrollFrame.cpp

@@ -3846,6 +3846,92 @@ void ScrollFrameHelper::MaybeAddTopLayerItems(nsDisplayListBuilder* aBuilder,
   }
 }
 
+nsRect ScrollFrameHelper::RestrictToRootCompositionBounds(
+    const nsRect& aDisplayportBase) {
+  nsPresContext* pc = mOuter->PresContext();
+  const nsPresContext* rootPresContext =
+      pc->GetToplevelContentDocumentPresContext();
+  if (!rootPresContext) {
+    rootPresContext = pc->GetRootPresContext();
+  }
+  if (!rootPresContext) {
+    return aDisplayportBase;
+  }
+  const mozilla::PresShell* const rootPresShell = rootPresContext->PresShell();
+  nsIFrame* rootFrame = rootPresShell->GetRootScrollFrame();
+  if (!rootFrame) {
+    rootFrame = rootPresShell->GetRootFrame();
+  }
+  if (!rootFrame) {
+    return aDisplayportBase;
+  }
+  nsRect rootCompBounds = nsRect(
+      nsPoint(0, 0),
+      nsLayoutUtils::CalculateCompositionSizeForFrame(rootFrame));
+
+  // If rootFrame is the RCD-RSF then
+  // CalculateCompositionSizeForFrame did not take the document's
+  // resolution into account, so we must.
+  if (rootPresContext->IsRootContentDocument() &&
+      rootFrame == rootPresShell->GetRootScrollFrame()) {
+    rootCompBounds = rootCompBounds.RemoveResolution(
+        rootPresShell->GetResolution());
+  }
+
+  // We want to convert the root composition bounds from the
+  // coordinate space of |rootFrame| to the coordinate space of
+  // |mOuter|. We do that with the TransformRect call below.
+  // However, since we care about the root composition bounds
+  // relative to what the user is actually seeing, we also need to
+  // incorporate the APZ callback transforms into this. Most of the
+  // time those transforms are negligible, but in some cases (e.g.
+  // when a zoom is applied on an overflow:hidden document) it is
+  // not (see bug 1280013).
+  // XXX: Eventually we may want to create a modified version of
+  // TransformRect that includes the APZ callback transforms
+  // directly.
+  nsLayoutUtils::TransformRect(rootFrame, mOuter, rootCompBounds);
+  rootCompBounds += CSSPoint::ToAppUnits(
+      nsLayoutUtils::GetCumulativeApzCallbackTransform(mOuter));
+
+  // We want to limit aDisplayportBase to be no larger than
+  // rootCompBounds on either axis, but we don't want to just
+  // blindly intersect the two, because rootCompBounds might be
+  // offset from where aDisplayportBase is (see bug 1327095 comment
+  // 8). Instead, we translate rootCompBounds so as to maximize the
+  // overlap with aDisplayportBase, and *then* do the intersection.
+  if (rootCompBounds.x > aDisplayportBase.x &&
+      rootCompBounds.XMost() > aDisplayportBase.XMost()) {
+    // rootCompBounds is at a greater x-position for both left and
+    // right, so translate it such that the XMost() values are the
+    // same. This will line up the right edge of the two rects, and
+    // might mean that rootCompbounds.x is smaller than
+    // aDisplayportBase.x. We can avoid that by taking the min of the
+    // x delta and XMost() delta, but it doesn't really matter
+    // because the intersection between the two rects below will end
+    // up the same.
+    rootCompBounds.x -=
+        (rootCompBounds.XMost() - aDisplayportBase.XMost());
+  } else if (rootCompBounds.x < aDisplayportBase.x &&
+             rootCompBounds.XMost() < aDisplayportBase.XMost()) {
+    // Analaogous code for when the rootCompBounds is at a smaller
+    // x-position.
+    rootCompBounds.x = aDisplayportBase.x;
+  }
+  // Do the same for y-axis
+  if (rootCompBounds.y > aDisplayportBase.y &&
+      rootCompBounds.YMost() > aDisplayportBase.YMost()) {
+    rootCompBounds.y -=
+        (rootCompBounds.YMost() - aDisplayportBase.YMost());
+  } else if (rootCompBounds.y < aDisplayportBase.y &&
+             rootCompBounds.YMost() < aDisplayportBase.YMost()) {
+    rootCompBounds.y = aDisplayportBase.y;
+  }
+
+  // Now we can do the intersection
+  return aDisplayportBase.Intersect(rootCompBounds);
+}
+
 bool ScrollFrameHelper::DecideScrollableLayer(
     nsDisplayListBuilder* aBuilder, nsRect* aVisibleRect, nsRect* aDirtyRect,
     bool aSetBase, bool* aDirtyRectHasBeenOverriden) {
@@ -3876,88 +3962,8 @@ bool ScrollFrameHelper::DecideScrollableLayer(
         // Only restrict to the root composition bounds if necessary,
         // as the required coordinate transformation is expensive.
         if (usingDisplayPort) {
-          const nsPresContext* rootPresContext =
-              pc->GetToplevelContentDocumentPresContext();
-          if (!rootPresContext) {
-            rootPresContext = pc->GetRootPresContext();
-          }
-          if (rootPresContext) {
-            const mozilla::PresShell* const rootPresShell =
-                rootPresContext->PresShell();
-            nsIFrame* rootFrame = rootPresShell->GetRootScrollFrame();
-            if (!rootFrame) {
-              rootFrame = rootPresShell->GetRootFrame();
-            }
-            if (rootFrame) {
-              nsRect rootCompBounds = nsRect(
-                  nsPoint(0, 0),
-                  nsLayoutUtils::CalculateCompositionSizeForFrame(rootFrame));
-
-              // If rootFrame is the RCD-RSF then
-              // CalculateCompositionSizeForFrame did not take the document's
-              // resolution into account, so we must.
-              if (rootPresContext->IsRootContentDocument() &&
-                  rootFrame == rootPresShell->GetRootScrollFrame()) {
-                rootCompBounds = rootCompBounds.RemoveResolution(
-                    rootPresShell->GetResolution());
-              }
-
-              // We want to convert the root composition bounds from the
-              // coordinate space of |rootFrame| to the coordinate space of
-              // |mOuter|. We do that with the TransformRect call below.
-              // However, since we care about the root composition bounds
-              // relative to what the user is actually seeing, we also need to
-              // incorporate the APZ callback transforms into this. Most of the
-              // time those transforms are negligible, but in some cases (e.g.
-              // when a zoom is applied on an overflow:hidden document) it is
-              // not (see bug 1280013).
-              // XXX: Eventually we may want to create a modified version of
-              // TransformRect that includes the APZ callback transforms
-              // directly.
-              nsLayoutUtils::TransformRect(rootFrame, mOuter, rootCompBounds);
-              rootCompBounds += CSSPoint::ToAppUnits(
-                  nsLayoutUtils::GetCumulativeApzCallbackTransform(mOuter));
-
-              // We want to limit displayportBase to be no larger than
-              // rootCompBounds on either axis, but we don't want to just
-              // blindly intersect the two, because rootCompBounds might be
-              // offset from where displayportBase is (see bug 1327095 comment
-              // 8). Instead, we translate rootCompBounds so as to maximize the
-              // overlap with displayportBase, and *then* do the intersection.
-              if (rootCompBounds.x > displayportBase.x &&
-                  rootCompBounds.XMost() > displayportBase.XMost()) {
-                // rootCompBounds is at a greater x-position for both left and
-                // right, so translate it such that the XMost() values are the
-                // same. This will line up the right edge of the two rects, and
-                // might mean that rootCompbounds.x is smaller than
-                // displayportBase.x. We can avoid that by taking the min of the
-                // x delta and XMost() delta, but it doesn't really matter
-                // because the intersection between the two rects below will end
-                // up the same.
-                rootCompBounds.x -=
-                    (rootCompBounds.XMost() - displayportBase.XMost());
-              } else if (rootCompBounds.x < displayportBase.x &&
-                         rootCompBounds.XMost() < displayportBase.XMost()) {
-                // Analaogous code for when the rootCompBounds is at a smaller
-                // x-position.
-                rootCompBounds.x = displayportBase.x;
-              }
-              // Do the same for y-axis
-              if (rootCompBounds.y > displayportBase.y &&
-                  rootCompBounds.YMost() > displayportBase.YMost()) {
-                rootCompBounds.y -=
-                    (rootCompBounds.YMost() - displayportBase.YMost());
-              } else if (rootCompBounds.y < displayportBase.y &&
-                         rootCompBounds.YMost() < displayportBase.YMost()) {
-                rootCompBounds.y = displayportBase.y;
-              }
-
-              // Now we can do the intersection
-              displayportBase = displayportBase.Intersect(rootCompBounds);
-            }
-          }
+          displayportBase = RestrictToRootCompositionBounds(displayportBase);
         }
-
         displayportBase -= mScrollPort.TopLeft();
       }
 

layout/generic/nsGfxScrollFrame.h

@@ -433,6 +433,7 @@ class ScrollFrameHelper : public nsIReflowCallback {
   ScrollSnapInfo GetScrollSnapInfo(
       const mozilla::Maybe<nsPoint>& aDestination) const;
 
+  nsRect RestrictToRootCompositionBounds(const nsRect& aDisplayportBase);
   bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
                              nsRect* aVisibleRect, nsRect* aDirtyRect,
                              bool aSetBase,