Make WebView respond to device scale change

android_webview/java/src/org/chromium/android_webview/AwContents.java

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index a98057a4637da49194007cea9199dedd19c32741..982752913676fe86ccfebf81857c4f2adb4c70e2 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -297,7 +297,7 @@ public class AwContents implements SmartClipProvider,
     private Bitmap mFavicon;
     private boolean mHasRequestedVisitedHistoryFromClient;
     // TODO(boliu): This should be in a global context, not per webview.
-    private final double mDIPScale;
+    private double mDIPScale;
     // Whether this WebView is a popup.
     private boolean mIsPopupWindow = false;
 
@@ -700,6 +700,17 @@ public class AwContents implements SmartClipProvider,
         public void onConfigurationChanged(Configuration configuration) {
             setLocale(LocaleUtils.getLocale(configuration.locale));
             mSettings.updateAcceptLanguages();
+
+            DeviceDisplayInfo displayInfo = DeviceDisplayInfo.create(mContext);
+            // Update all display related parameters.
+            displayInfo.updateNativeSharedDisplayInfo();
+
+            final double newDIPScale = displayInfo.getDIPScale();
+            if (newDIPScale != mDIPScale) {
+                mContentViewCore.setDeviceScaleFactor((float) newDIPScale);
+                setDIPScale(newDIPScale);

[Tima Vaisburd, 2016/08/16 00:21:00]

Bo, as far as I understand you suggested to force resize here (I was going to
call ContentViewCoreImpl::WasResized()). But in my experiments the actual resize
always came after device scale change, no matter if hardcorded or in full screen
window. I guess Android does it for us?

[boliu, 2016/08/16 14:53:46]

That's just coming from the re-layout, because views above webview changed size.
We can't rely on it happening, hence calling WasResized here.

+                mContainerView.requestLayout();

[Tima Vaisburd, 2016/08/02 17:27:19]

Do we need to request layout on the container?

[boliu, 2016/08/02 18:09:27]

Don't think so. If the scale ends up needing a redraw, then wait until blink
sends the redraw message up through the normal invalidate path.

[Tima Vaisburd, 2016/08/16 00:21:01]

Removed mContainerView.requestLayout();

+            }
         }
     };
 
@@ -759,9 +770,7 @@ public class AwContents implements SmartClipProvider,
         mContentViewClient = new AwContentViewClient(contentsClient, settings, this, mContext);
         mLayoutSizer = dependencyFactory.createLayoutSizer();
         mSettings = settings;
-        mDIPScale = DeviceDisplayInfo.create(mContext).getDIPScale();
         mLayoutSizer.setDelegate(new AwLayoutSizerDelegate());
-        mLayoutSizer.setDIPScale(mDIPScale);
         mWebContentsDelegate = new AwWebContentsDelegateAdapter(
                 this, contentsClient, mContentViewClient, mContext, mContainerView);
         mContentsClientBridge = new AwContentsClientBridge(mContext, contentsClient,
@@ -792,7 +801,6 @@ public class AwContents implements SmartClipProvider,
         mDefaultVideoPosterRequestHandler = new DefaultVideoPosterRequestHandler(mContentsClient);
         mSettings.setDefaultVideoPosterURL(
                 mDefaultVideoPosterRequestHandler.getDefaultVideoPosterURL());
-        mSettings.setDIPScale(mDIPScale);
         mScrollOffsetManager =
                 dependencyFactory.createScrollOffsetManager(new AwScrollOffsetManagerDelegate());
         mScrollAccessibilityHelper = new ScrollAccessibilityHelper(mContainerView);
@@ -820,6 +828,13 @@ public class AwContents implements SmartClipProvider,
         return contentViewCore;
     }
 
+    private void setDIPScale(double dipScale) {
+        mDIPScale = dipScale;
+        nativeSetDipScale(mNativeAwContents, (float) mDIPScale);
+        mSettings.setDIPScale(mDIPScale);
+        mLayoutSizer.setDIPScale(mDIPScale);
+    }
+
     boolean isFullScreen() {
         return mFullScreenTransitionsState.isFullScreen();
     }
@@ -1048,7 +1063,10 @@ public class AwContents implements SmartClipProvider,
         mNavigationController = mWebContents.getNavigationController();
         installWebContentsObserver();
         mSettings.setWebContents(webContents);
-        nativeSetDipScale(mNativeAwContents, (float) mDIPScale);
+
+        // ContentViewCore requests and stores the device scale factor.
+        setDIPScale(mContentViewCore.getDeviceScaleFactor());
+
         updateContentViewCoreVisibility();
 
         // The native side object has been bound to this java instance, so now is the time to
@@ -3184,8 +3202,7 @@ public class AwContents implements SmartClipProvider,
             // to enter fixedLayoutSize mode is sent before the first resize
             // update.
             mLayoutSizer.onSizeChanged(w, h, ow, oh);
-            mContentViewCore.onPhysicalBackingSizeChanged(w, h);

[Tima Vaisburd, 2016/08/02 17:27:19]

onPhysicalBackingSizeChanges() calls nativeWasResized() that eventually gathers
ResizeParams and calls RenderWidget::OnResize().
ContentViewCoreImpl determines the viewport size in dip by getting the pixels
size and dividing it by the scale.
At the time of this call the pixels size is not yet updated and the ResizeParams
have |physical_backing_size| equal to the new size and the
|visible_viewport_size| corresponding to the old one.

At the next line mContentViewCore.onSizeChanged() calls 
RenderWidget::OnResize() again, now with correct sizes, but somehow it is too
late.

[boliu, 2016/08/02 18:09:27]

what do you mean by "late"?

It sounds like you are describing how things work today. why is this a problem
with this density change? basically I don't see why these two calls needs to be
merged into one (even though I agree it is weird they are separate)

[Tima Vaisburd, 2016/08/02 18:53:27]

I tried to explain why I merged these two calls but I did not get to the root
cause of the problem, that is, why the second call does not fix the issue.

[boliu, 2016/08/02 19:00:02]

Why would you expect it to "fix" anything? You said the DIPScale hasn't changed
in these calls here, right?

[Tima Vaisburd, 2016/08/16 00:21:00]

I restored the orininal code which means I need to find the root cause why these
two calls do not work.

-            mContentViewCore.onSizeChanged(w, h, ow, oh);
+            mContentViewCore.onBackingAndViewportSizeChanged(w, h, w, h, ow, oh);
             nativeOnSizeChanged(mNativeAwContents, w, h, ow, oh);
         }