Do not create dim layer until it gets a valid dimming request

If a window requests a dim of 0 and no blur, the dim surface gets created (because
technically someone is requesting to dim) and then immediately
destroyed (because alpha=0, blur=0 means that this layer should be destroyed as
it's useless). We can postpone creating a new surface until the window
requests a non 0 value.

Bug: 401449608
Test: DimmerTests
Flag: EXEMPT minor change
Change-Id: I11c97ae6401e3151df4941a5ec6ad42bb94357ce

2 files changed, 34 insertions, 2 deletions

diff --git a/services/core/java/com/android/server/wm/Dimmer.java b/services/core/java/com/android/server/wm/Dimmer.java
index 25fdf89afad1..2798e843d6dd 100644
--- a/services/core/java/com/android/server/wm/Dimmer.java
+++ b/services/core/java/com/android/server/wm/Dimmer.java
@@ -211,14 +211,17 @@ class Dimmer {
      * child should call setAppearance again to request the Dim to continue.
      * If multiple containers call this method, only the changes relative to the topmost will be
      * applied.
+     * The creation of the dim layer is delayed if the requested dim and blur are 0.
      * @param dimmingContainer  Container requesting the dim
      * @param alpha      Dim amount
      * @param blurRadius Blur amount
      */
     protected void adjustAppearance(@NonNull WindowState dimmingContainer,
                                     float alpha, int blurRadius) {
-        final DimState d = obtainDimState(dimmingContainer);
-        d.prepareLookChange(alpha, blurRadius);
+        if (mDimState != null || (alpha != 0 || blurRadius != 0)) {
+            final DimState d = obtainDimState(dimmingContainer);
+            d.prepareLookChange(alpha, blurRadius);
+        }
     }
 
     /**
diff --git a/services/tests/wmtests/src/com/android/server/wm/DimmerTests.java b/services/tests/wmtests/src/com/android/server/wm/DimmerTests.java
index a30591ea7b15..9486bc522a9c 100644
--- a/services/tests/wmtests/src/com/android/server/wm/DimmerTests.java
+++ b/services/tests/wmtests/src/com/android/server/wm/DimmerTests.java
@@ -25,6 +25,7 @@ import static com.android.server.wm.utils.LastCallVerifier.lastCall;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.eq;
@@ -432,4 +433,32 @@ public class DimmerTests extends WindowTestsBase {
         verify(mTransaction, never()).setAlpha(dimLayer, 0.5f);
         verify(mTransaction).setAlpha(dimLayer, 0.9f);
     }
+
+    /**
+     * A window requesting to dim to 0 and without blur would cause the dim to be created and
+     * destroyed continuously.
+     * Ensure the dim layer is not created until the window is requesting valid values.
+     */
+    @Test
+    public void testDimNotCreatedIfNoAlphaNoBlur() {
+        mDimmer.adjustAppearance(mChild1, 0.0f, 0);
+        mDimmer.adjustPosition(mChild1, mChild1);
+        assertNull(mDimmer.getDimLayer());
+        mDimmer.updateDims(mTransaction);
+        assertNull(mDimmer.getDimLayer());
+
+        mDimmer.adjustAppearance(mChild1, 0.9f, 0);
+        mDimmer.adjustPosition(mChild1, mChild1);
+        assertNotNull(mDimmer.getDimLayer());
+    }
+
+    /**
+     * If there is a blur, then the dim layer is created even though alpha is 0
+     */
+    @Test
+    public void testDimCreatedIfNoAlphaButHasBlur() {
+        mDimmer.adjustAppearance(mChild1, 0.0f, 10);
+        mDimmer.adjustPosition(mChild1, mChild1);
+        assertNotNull(mDimmer.getDimLayer());
+    }
 }