Bug 1509552 - MobileViewportManager::UpdateResolution cleanup, part 2. r=kats

* Call SetResolutionAndScaleTo() in just one place
* Call UpdateVisualViewportSize() in UpdateResolution() rather than
  requiring the caller to do it (and on non-first paints, only call it
  if the resolution has actually changed)

Differential Revision: https://phabricator.services.mozilla.com/D13313

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

layout/base/MobileViewportManager.cpp

@@ -239,7 +239,7 @@ ZoomToResolution(CSSToScreenScale aZoom,
     / aCssToDev * ParentLayerToLayerScale(1);
 }
 
-CSSToScreenScale
+void
 MobileViewportManager::UpdateResolution(const nsViewportInfo& aViewportInfo,
                                         const ScreenIntSize& aDisplaySize,
                                         const CSSSize& aViewport,
@@ -249,6 +249,7 @@ MobileViewportManager::UpdateResolution(const nsViewportInfo& aViewportInfo,
       mPresShell->GetPresContext()->CSSToDevPixelScale();
   LayoutDeviceToLayerScale res(mPresShell->GetResolution());
   CSSToScreenScale zoom = ResolutionToZoom(res, cssToDev);
+  Maybe<CSSToScreenScale> newZoom;
 
   if (mIsFirstPaint) {
     ScreenIntSize compositionSize = GetCompositionSize(aDisplaySize);
@@ -283,15 +284,9 @@ MobileViewportManager::UpdateResolution(const nsViewportInfo& aViewportInfo,
     MOZ_ASSERT(aViewportInfo.GetMinZoom() <= defaultZoom &&
       defaultZoom <= aViewportInfo.GetMaxZoom());
 
-    zoom = defaultZoom;
-
-    LayoutDeviceToLayerScale resolution = ZoomToResolution(zoom, cssToDev);
-    MVM_LOG("%p: setting resolution %f\n", this, resolution.scale);
-    mPresShell->SetResolutionAndScaleTo(resolution.scale);
-
-    return zoom;
-  }
-
+    // On first paint, we always consider the zoom to have changed.
+    newZoom = Some(defaultZoom);
+  } else {
     // If this is not a first paint, then in some cases we want to update the pre-
     // existing resolution so as to maintain how much actual content is visible
     // within the display width. Note that "actual content" may be different with
@@ -318,12 +313,21 @@ MobileViewportManager::UpdateResolution(const nsViewportInfo& aViewportInfo,
     //    tag is added or removed)
     // 4. neither screen size nor CSS viewport changes
     if (aDisplayWidthChangeRatio) {
-    zoom = ScaleZoomWithDisplayWidth(zoom, aDisplayWidthChangeRatio.value(),
-      aViewport, mMobileViewportSize);
-    mPresShell->SetResolutionAndScaleTo(ZoomToResolution(zoom, cssToDev).scale);
+      newZoom = Some(ScaleZoomWithDisplayWidth(zoom, aDisplayWidthChangeRatio.value(),
+        aViewport, mMobileViewportSize));
+    }
   }
 
-  return zoom;
+  // If the zoom has changed, update the pres shell resolution and the
+  // visual viewport size accordingly.
+  if (newZoom) {
+    LayoutDeviceToLayerScale resolution = ZoomToResolution(*newZoom, cssToDev);
+    MVM_LOG("%p: setting resolution %f\n", this, resolution.scale);
+    mPresShell->SetResolutionAndScaleTo(resolution.scale);
+
+    MVM_LOG("%p: New zoom is %f\n", this, newZoom->scale);
+    UpdateVisualViewportSize(aDisplaySize, *newZoom);
+  }
 }
 
 
@@ -463,10 +467,7 @@ MobileViewportManager::RefreshViewportSize(bool aForceAdjustResolution)
     mIsFirstPaint, mMobileViewportSize != viewport);
 
   if (gfxPrefs::APZAllowZooming()) {
-    CSSToScreenScale zoom = UpdateResolution(viewportInfo, displaySize, viewport,
-      displayWidthChangeRatio);
-    MVM_LOG("%p: New zoom is %f\n", this, zoom.scale);
-    UpdateVisualViewportSize(displaySize, zoom);
+    UpdateResolution(viewportInfo, displaySize, viewport, displayWidthChangeRatio);
   }
   if (gfxPlatform::AsyncPanZoomEnabled()) {
     UpdateDisplayPortMargins();
@@ -517,10 +518,6 @@ MobileViewportManager::ShrinkToDisplaySizeIfNeeded(
       nsLayoutUtils::CalculateScrollableRectForFrame(rootScrollableFrame,
                                                      nullptr);
     CSSSize contentSize = CSSSize::FromAppUnits(scrollableRect.Size());
-    CSSToScreenScale zoom =
     UpdateResolution(aViewportInfo, aDisplaySize, contentSize, Nothing());
-
-    MVM_LOG("%p: Adapted zoom is %f\n", this, zoom.scale);
-    UpdateVisualViewportSize(aDisplaySize, zoom);
   }
 }

layout/base/MobileViewportManager.h

@@ -93,8 +93,8 @@ public:
                             const mozilla::CSSSize& aNewViewport,
                             const mozilla::CSSSize& aOldViewport);
 
-  /* Updates the presShell resolution and returns the new zoom. */
-  mozilla::CSSToScreenScale UpdateResolution(const nsViewportInfo& aViewportInfo,
+  /* Updates the presShell resolution and the visual viewport size. */
+  void UpdateResolution(const nsViewportInfo& aViewportInfo,
                         const mozilla::ScreenIntSize& aDisplaySize,
                         const mozilla::CSSSize& aViewport,
                         const mozilla::Maybe<float>& aDisplayWidthChangeRatio);