Enforce background fallback to be non-translucent

To avoid screen garbage or wallpaper shining through, the background
we use there for filling the whole needs to

a) Be non-translucent in all cases except if the window is translucent.
b) Don't infer it from the theme as it might be unexpected. Don't define
it in the theme, and use black if it's not defined.

Bug: 28763785
Change-Id: Ifb724b5c5feea3ed70d68e5bd7615fa91185e743

3 files changed, 39 insertions, 9 deletions

diff --git a/core/java/com/android/internal/policy/DecorView.java b/core/java/com/android/internal/policy/DecorView.java
index f5966362fdb2..a0652197d7b4 100644
--- a/core/java/com/android/internal/policy/DecorView.java
+++ b/core/java/com/android/internal/policy/DecorView.java
@@ -45,6 +45,7 @@ import android.graphics.PixelFormat;
 import android.graphics.Rect;
 import android.graphics.Region;
 import android.graphics.Shader;
+import android.graphics.drawable.ColorDrawable;
 import android.graphics.drawable.Drawable;
 import android.os.RemoteException;
 import android.util.DisplayMetrics;
@@ -907,10 +908,12 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         if (getBackground() != drawable) {
             setBackgroundDrawable(drawable);
             if (drawable != null) {
-                mResizingBackgroundDrawable = drawable;
+                mResizingBackgroundDrawable = enforceNonTranslucentBackground(drawable,
+                        mWindow.isTranslucent() || mWindow.isShowingWallpaper());
             } else {
                 mResizingBackgroundDrawable = getResizingBackgroundDrawable(
-                        getContext(), 0, mWindow.mBackgroundFallbackResource);
+                        getContext(), 0, mWindow.mBackgroundFallbackResource,
+                        mWindow.isTranslucent() || mWindow.isShowingWallpaper());
             }
             if (mResizingBackgroundDrawable != null) {
                 mResizingBackgroundDrawable.getPadding(mBackgroundPadding);
@@ -1785,7 +1788,8 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
     private void loadBackgroundDrawablesIfNeeded() {
         if (mResizingBackgroundDrawable == null) {
             mResizingBackgroundDrawable = getResizingBackgroundDrawable(getContext(),
-                    mWindow.mBackgroundResource, mWindow.mBackgroundFallbackResource);
+                    mWindow.mBackgroundResource, mWindow.mBackgroundFallbackResource,
+                    mWindow.isTranslucent() || mWindow.isShowingWallpaper());
             if (mResizingBackgroundDrawable == null) {
                 // We shouldn't really get here as the background fallback should be always
                 // available since it is defaulted by the system.
@@ -1893,21 +1897,41 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
      * user is resizing the window of an activity in multi-window mode.
      */
     public static Drawable getResizingBackgroundDrawable(Context context, int backgroundRes,
-            int backgroundFallbackRes) {
+            int backgroundFallbackRes, boolean windowTranslucent) {
         if (backgroundRes != 0) {
             final Drawable drawable = context.getDrawable(backgroundRes);
             if (drawable != null) {
-                return drawable;
+                return enforceNonTranslucentBackground(drawable, windowTranslucent);
             }
         }
 
         if (backgroundFallbackRes != 0) {
             final Drawable fallbackDrawable = context.getDrawable(backgroundFallbackRes);
             if (fallbackDrawable != null) {
-                return fallbackDrawable;
+                return enforceNonTranslucentBackground(fallbackDrawable, windowTranslucent);
             }
         }
-        return null;
+        return new ColorDrawable(Color.BLACK);
+    }
+
+    /**
+     * Enforces a drawable to be non-translucent to act as a background if needed, i.e. if the
+     * window is not translucent.
+     */
+    private static Drawable enforceNonTranslucentBackground(Drawable drawable,
+            boolean windowTranslucent) {
+        if (!windowTranslucent && drawable instanceof ColorDrawable) {
+            ColorDrawable colorDrawable = (ColorDrawable) drawable;
+            int color = colorDrawable.getColor();
+            if (Color.alpha(color) != 255) {
+                ColorDrawable copy = (ColorDrawable) colorDrawable.getConstantState().newDrawable()
+                        .mutate();
+                copy.setColor(
+                        Color.argb(255, Color.red(color), Color.green(color), Color.blue(color)));
+                return copy;
+            }
+        }
+        return drawable;
     }
 
     /**
@@ -2037,7 +2061,7 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
     private void drawResizingShadowIfNeeded(DisplayListCanvas canvas) {
         if (mResizeMode != RESIZE_MODE_DOCKED_DIVIDER || mWindow.mIsFloating
                 || mWindow.isTranslucent()
-                || (mWindow.getAttributes().flags & FLAG_SHOW_WALLPAPER) != 0) {
+                || mWindow.isShowingWallpaper()) {
             return;
         }
         canvas.save();
diff --git a/core/java/com/android/internal/policy/PhoneWindow.java b/core/java/com/android/internal/policy/PhoneWindow.java
index 4f15ece8e04e..9ad750d3a599 100644
--- a/core/java/com/android/internal/policy/PhoneWindow.java
+++ b/core/java/com/android/internal/policy/PhoneWindow.java
@@ -509,6 +509,13 @@ public class PhoneWindow extends Window implements MenuBuilder.Callback {
     }
 
     /**
+     * @return Whether the window is currently showing the wallpaper.
+     */
+    boolean isShowingWallpaper() {
+        return (getAttributes().flags & FLAG_SHOW_WALLPAPER) != 0;
+    }
+
+    /**
      * Return a LayoutInflater instance that can be used to inflate XML view layout
      * resources for use in this Window.
      *
diff --git a/core/res/res/values/themes.xml b/core/res/res/values/themes.xml
index 998eea5ac9ab..aecda44a6583 100644
--- a/core/res/res/values/themes.xml
+++ b/core/res/res/values/themes.xml
@@ -174,7 +174,6 @@ please see themes_device_defaults.xml.
 
         <!-- Window attributes -->
         <item name="windowBackground">@drawable/screen_background_selector_dark</item>
-        <item name="windowBackgroundFallback">?attr/colorBackground</item>
         <item name="windowClipToOutline">false</item>
         <item name="windowFrame">@null</item>
         <item name="windowNoTitle">false</item>