Create listener for dynamic blurEnabled changes

This CL exposes an API to let apps know when the blur has been enabled
or disabled dynamically.

This could be due to battery saving mode turned on, tunnel mode being
used, minimal post processing requested, etc.

This adds a WindowManager.addCrossWindowBlurEnabledListener, which allows
apps to add/remove a listener for blur enabled state changes. The
listeners are registered in a CrossWindowBlurListeners, which receives
updates from WindowManagerService when blurEnabled changes.
CrossWindowBlurListeners only registers a remote listener if the client
initializes it. I.e. if the app is not interested in blurs, the
CrossWindowBlurListeners won't get initialized and won't register a
remote listener.

WindowManagerService holds a RemoteCallbackList, which holds listeners
for each client process and notifies them when there are updates. If any
of the listeners' process dies, the entry is removed from the list.

Bug: 177524486
Test: m
CTS-Coverage-Bug: 179990440
Change-Id: I3fe8f2d2008171d6b069e8ee6f3b47e5b5d60cfa

1 files changed, 70 insertions, 1 deletions

diff --git a/core/java/android/view/WindowManager.java b/core/java/android/view/WindowManager.java
index 2889e11e6f1f..2053826d91a9 100644
--- a/core/java/android/view/WindowManager.java
+++ b/core/java/android/view/WindowManager.java
@@ -121,6 +121,7 @@ import java.lang.annotation.RetentionPolicy;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
+import java.util.function.Consumer;
 
 /**
  * The interface that apps use to talk to the window manager.
@@ -809,6 +810,64 @@ public interface WindowManager extends ViewManager {
         return DISPLAY_IME_POLICY_FALLBACK_DISPLAY;
     }
 
+    /**
+     * Returns whether cross-window blur is currently enabled. This affects both window blur behind
+     * (see {@link LayoutParams#setBlurBehindRadius}) and window background blur (see
+     * {@link Window#setBackgroundBlurRadius}).
+     *
+     * Cross-window blur might not be supported by some devices due to GPU limitations. It can also
+     * be disabled at runtime, e.g. during battery saving mode, when multimedia tunneling is used or
+     * when minimal post processing is requested. In such situations, no blur will be computed or
+     * drawn, so the blur target area will not be blurred. To handle this, the app might want to
+     * change its theme to one that does not use blurs. To listen for cross-window blur
+     * enabled/disabled events, use {@link #addCrossWindowBlurEnabledListener}.
+     *
+     * @see #addCrossWindowBlurEnabledListener
+     * @see LayoutParams#setBlurBehindRadius
+     * @see Window#setBackgroundBlurRadius
+     */
+    default boolean isCrossWindowBlurEnabled() {
+        return false;
+    }
+
+    /**
+     * Adds a listener, which will be called when cross-window blurs are enabled/disabled at
+     * runtime. This affects both window blur behind (see {@link LayoutParams#setBlurBehindRadius})
+     * and window background blur (see {@link Window#setBackgroundBlurRadius}).
+     *
+     * Cross-window blur might not be supported by some devices due to GPU limitations. It can also
+     * be disabled at runtime, e.g. during battery saving mode, when multimedia tunneling is used or
+     * when minimal post processing is requested. In such situations, no blur will be computed or
+     * drawn, so the blur target area will not be blurred. To handle this, the app might want to
+     * change its theme to one that does not use blurs.
+     *
+     * The listener will be called on the main thread.
+     *
+     * If the listener is added successfully, it will be called immediately with the current
+     * cross-window blur enabled state.
+     *
+     *
+     * @param listener the listener to be added. It will be called back with a boolean parameter,
+     *                 which is true if cross-window blur is enabled and false if it is disabled
+     *
+     * @see #removeCrossWindowBlurEnabledListener
+     * @see #isCrossWindowBlurEnabled
+     * @see LayoutParams#setBlurBehindRadius
+     * @see Window#setBackgroundBlurRadius
+     */
+    default void addCrossWindowBlurEnabledListener(@NonNull Consumer<Boolean> listener) {
+    }
+
+    /**
+     * Removes a listener, previously added with {@link #addCrossWindowBlurEnabledListener}
+     *
+     * @param listener the listener to be removed
+     *
+     * @see #addCrossWindowBlurEnabledListener
+     */
+    default void removeCrossWindowBlurEnabledListener(@NonNull Consumer<Boolean> listener) {
+    }
+
     public static class LayoutParams extends ViewGroup.LayoutParams implements Parcelable {
         /**
          * X position for this window.  With the default gravity it is ignored.
@@ -3537,7 +3596,8 @@ public interface WindowManager extends ViewManager {
 
         /**
          * Blurs the screen behind the window. The effect is similar to that of {@link #dimAmount},
-         * but instead of dimmed, the content behind the window will be blurred.
+         * but instead of dimmed, the content behind the window will be blurred (or combined with
+         * the dim amount, if such is specified).
          *
          * The density of the blur is set by the blur radius. The radius defines the size
          * of the neighbouring area, from which pixels will be averaged to form the final
@@ -3550,10 +3610,19 @@ public interface WindowManager extends ViewManager {
          *
          * Requires {@link #FLAG_BLUR_BEHIND} to be set.
          *
+         * Cross-window blur might not be supported by some devices due to GPU limitations. It can
+         * also be disabled at runtime, e.g. during battery saving mode, when multimedia tunneling
+         * is used or when minimal post processing is requested. In such situations, no blur will
+         * be computed or drawn, resulting in there being no depth separation between the window
+         * and the content behind it. To avoid this, the app might want to use more
+         * {@link #dimAmount} on its window. To listen for cross-window blur enabled/disabled
+         * events, use {@link #addCrossWindowBlurEnabledListener}.
+         *
          * @param blurBehindRadius The blur radius to use for blur behind in pixels
          *
          * @see #FLAG_BLUR_BEHIND
          * @see #getBlurBehindRadius
+         * @see WindowManager#addCrossWindowBlurEnabledListener
          * @see Window#setBackgroundBlurRadius
          */
         public void setBlurBehindRadius(@IntRange(from = 0) int blurBehindRadius) {