Bug 1556556 - Move GetCallbackTransform() into a new ViewportUtils class. r=kats

This function (and helper functions that wrap it) will be used extensively
throughout layout code, so keeping it in APZCCallbackHelper seems awkward.

nsLayoutUtils would also be a reasonable place but has the downside that
adding a new function to it triggers recompiling the world.

Differential Revision: https://phabricator.services.mozilla.com/D68296

gfx/layers/apz/util/APZCCallbackHelper.cpp

@@ -20,6 +20,7 @@
 #include "mozilla/layers/WebRenderBridgeChild.h"
 #include "mozilla/PresShell.h"
 #include "mozilla/TouchEvents.h"
+#include "mozilla/ViewportUtils.h"
 #include "nsContainerFrame.h"
 #include "nsContentUtils.h"
 #include "nsIContent.h"
@@ -451,38 +452,6 @@ PresShell* APZCCallbackHelper::GetRootContentDocumentPresShellForContent(
   return context->PresShell();
 }
 
-mozilla::CSSToCSSMatrix4x4 APZCCallbackHelper::GetCallbackTransform(
-    ScrollableLayerGuid::ViewID aScrollId) {
-  if (aScrollId == ScrollableLayerGuid::NULL_SCROLL_ID) {
-    return {};
-  }
-  nsCOMPtr<nsIContent> content = nsLayoutUtils::FindContentFor(aScrollId);
-  if (!content) {
-    return {};
-  }
-
-  // First, scale inversely by the root content document's pres shell
-  // resolution to cancel the scale-to-resolution transform that the
-  // compositor adds to the layer with the pres shell resolution. The points
-  // sent to Gecko by APZ don't have this transform unapplied (unlike other
-  // compositor-side transforms) because Gecko needs it applied when hit
-  // testing against content that's conceptually outside the resolution,
-  // such as scrollbars.
-  float resolution = 1.0f;
-  if (PresShell* presShell =
-          GetRootContentDocumentPresShellForContent(content)) {
-    resolution = presShell->GetResolution();
-  }
-
-  // Now apply the callback-transform. This is only approximately correct,
-  // see the comment on GetCumulativeApzCallbackTransform for details.
-  CSSPoint transform = nsLayoutUtils::GetCumulativeApzCallbackTransform(
-      content->GetPrimaryFrame());
-
-  return mozilla::CSSToCSSMatrix4x4::Scaling(1 / resolution, 1 / resolution, 1)
-      .PostTranslate(transform.x, transform.y, 0);
-}
-
 nsEventStatus APZCCallbackHelper::DispatchWidgetEvent(WidgetGUIEvent& aEvent) {
   nsEventStatus status = nsEventStatus_eConsumeNoDefault;
   if (aEvent.mWidget) {

gfx/layers/apz/util/APZCCallbackHelper.h

@@ -98,23 +98,6 @@ class APZCCallbackHelper {
   static PresShell* GetRootContentDocumentPresShellForContent(
       nsIContent* aContent);
 
-  /* Return a "callback transform" to be applied to the coordinates of input
-     events targeting content inside the scroll frame identified by |aScrollId|.
-     The callback transform has two components:
-       1. The pres shell resolution, representing the pinch-zoom scale
-          (if the scroll frame |aScrollId| is inside the resolution, which
-          is most of the time).
-       2. A translation representing async scrolling. This can contain:
-           - For any scroll frame, a scroll component resulting from the main
-             thread incompletely applying an APZ-requested scroll position.
-           - For the RCD-RSF only, a persistent component representing the
-             offset of the visual viewport relative to the layout viewport.
-         The translation is accumulated for all scroll frames form |aScrollId|
-         up to the root, using values populated in UpdateCallbackTransform. See
-         that method's documentation for additional details. */
-  static CSSToCSSMatrix4x4 GetCallbackTransform(
-      ScrollableLayerGuid::ViewID aScrollId);
-
   /* Dispatch a widget event via the widget stored in the event, if any.
    * In a child process, allows the BrowserParent event-capture mechanism to
    * intercept the event. */

layout/base/ViewportUtils.cpp

@@ -0,0 +1,50 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/PresShell.h"
+#include "mozilla/ViewportUtils.h"
+#include "mozilla/layers/APZCCallbackHelper.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+#include "nsIContent.h"
+#include "nsLayoutUtils.h"
+
+namespace mozilla {
+
+using layers::APZCCallbackHelper;
+using layers::ScrollableLayerGuid;
+
+CSSToCSSMatrix4x4 ViewportUtils::GetCallbackTransform(
+    ScrollableLayerGuid::ViewID aScrollId) {
+  if (aScrollId == ScrollableLayerGuid::NULL_SCROLL_ID) {
+    return {};
+  }
+  nsCOMPtr<nsIContent> content = nsLayoutUtils::FindContentFor(aScrollId);
+  if (!content) {
+    return {};
+  }
+
+  // First, scale inversely by the root content document's pres shell
+  // resolution to cancel the scale-to-resolution transform that the
+  // compositor adds to the layer with the pres shell resolution. The points
+  // sent to Gecko by APZ don't have this transform unapplied (unlike other
+  // compositor-side transforms) because Gecko needs it applied when hit
+  // testing against content that's conceptually outside the resolution,
+  // such as scrollbars.
+  float resolution = 1.0f;
+  if (PresShell* presShell =
+          APZCCallbackHelper::GetRootContentDocumentPresShellForContent(
+              content)) {
+    resolution = presShell->GetResolution();
+  }
+
+  // Now apply the callback-transform. This is only approximately correct,
+  // see the comment on GetCumulativeApzCallbackTransform for details.
+  CSSPoint transform = nsLayoutUtils::GetCumulativeApzCallbackTransform(
+      content->GetPrimaryFrame());
+
+  return mozilla::CSSToCSSMatrix4x4::Scaling(1 / resolution, 1 / resolution, 1)
+      .PostTranslate(transform.x, transform.y, 0);
+}
+
+}  // namespace mozilla

layout/base/ViewportUtils.h

@@ -0,0 +1,36 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_ViewportUtils_h
+#define mozilla_ViewportUtils_h
+
+#include "Units.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+
+namespace mozilla {
+
+class ViewportUtils {
+ public:
+  /* Return a "callback transform" to be applied to the coordinates of input
+     events targeting content inside the scroll frame identified by |aScrollId|.
+     The callback transform has two components:
+     1. The pres shell resolution, representing the pinch-zoom scale
+        (if the scroll frame |aScrollId| is inside the resolution, which
+        is most of the time).
+     2. A translation representing async scrolling. This can contain:
+         - For any scroll frame, a scroll component resulting from the main
+           thread incompletely applying an APZ-requested scroll position.
+         - For the RCD-RSF only, a persistent component representing the
+           offset of the visual viewport relative to the layout viewport.
+       The translation is accumulated for all scroll frames form |aScrollId|
+       up to the root, using values populated in
+       APZCCallbackHelper::UpdateCallbackTransform. See that method's
+       documentation for additional details. */
+  static CSSToCSSMatrix4x4 GetCallbackTransform(
+      layers::ScrollableLayerGuid::ViewID aScrollId);
+};
+
+}  // namespace mozilla
+
+#endif /* mozilla_ViewportUtils_h */

layout/base/moz.build

@@ -87,6 +87,7 @@ EXPORTS.mozilla += [
     'ScrollTypes.h',
     'ShapeUtils.h',
     'StaticPresData.h',
+    'ViewportUtils.h',
 ]
 
 EXPORTS.mozilla.layout += [
@@ -129,6 +130,7 @@ UNIFIED_SOURCES += [
     'StackArena.cpp',
     'StaticPresData.cpp',
     'TouchManager.cpp',
+    'ViewportUtils.cpp',
     'ZoomConstraintsClient.cpp',
 ]
 

layout/base/nsDocumentViewer.cpp

@@ -19,6 +19,7 @@
 #include "nsIContent.h"
 #include "nsIContentViewer.h"
 #include "nsIDocumentViewerPrint.h"
+#include "nsIScreen.h"
 #include "mozilla/dom/BrowsingContext.h"
 #include "mozilla/dom/BeforeUnloadEvent.h"
 #include "mozilla/dom/PopupBlocker.h"