Don't shown letterbox surfaces unless activity is visible.

Also, merging visibility and "surface ready" checks in LetterboxUiController#shouldShowLetterboxUi because other UI parts of letterbox like rounded corners and background also shouldn't be applied until those conditions are true.

Fix: 185955096
Test: atest WmTests:SizeCompatTests
Change-Id: I5822d651ff65c17fce4891b8728546bec235e54f

services/core/java/com/android/server/wm/LetterboxUiController.java

@@ -128,12 +128,9 @@ final class LetterboxUiController {
         if (w == null || winHint != null && w != winHint) {
             return;
         }
-        final boolean surfaceReady = w.isDrawn()  // Regular case
-                || w.isDragResizeChanged();  // Waiting for relayoutWindow to call preserveSurface.
-        final boolean needsLetterbox = surfaceReady && shouldShowLetterboxUi(w);
         updateRoundedCorners(w);
         updateWallpaperForLetterbox(w);
-        if (needsLetterbox) {
+        if (shouldShowLetterboxUi(w)) {
             if (mLetterbox == null) {
                 mLetterbox = new Letterbox(() -> mActivityRecord.makeChildSurface(null),
                         mActivityRecord.mWmService.mTransactionFactory,
@@ -161,19 +158,26 @@ final class LetterboxUiController {
         }
     }
 
-    /**
-     * @return {@code true} when the main window is letterboxed, this activity isn't transparent
-     * and doesn't show a wallpaper.
-     */
     @VisibleForTesting
     boolean shouldShowLetterboxUi(WindowState mainWindow) {
-        return mainWindow.areAppWindowBoundsLetterboxed() && mActivityRecord.fillsParent()
+        return isSurfaceReadyAndVisible(mainWindow) && mainWindow.areAppWindowBoundsLetterboxed()
+                // Check that an activity isn't transparent.
+                && mActivityRecord.fillsParent()
                 // Check for FLAG_SHOW_WALLPAPER explicitly instead of using
                 // WindowContainer#showWallpaper because the later will return true when this
                 // activity is using blurred wallpaper for letterbox backgroud.
                 && (mainWindow.mAttrs.flags & FLAG_SHOW_WALLPAPER) == 0;
     }
 
+    @VisibleForTesting
+    boolean isSurfaceReadyAndVisible(WindowState mainWindow) {
+        boolean surfaceReady = mainWindow.isDrawn() // Regular case
+                // Waiting for relayoutWindow to call preserveSurface
+                || mainWindow.isDragResizeChanged();
+        return surfaceReady && (mActivityRecord.isVisible()
+                || mActivityRecord.isVisibleRequested());
+    }
+
     private Color getLetterboxBackgroundColor() {
         final WindowState w = mActivityRecord.findMainWindow();
         if (w == null || w.isLetterboxedForDisplayCutout()) {

services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java

@@ -50,6 +50,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.same;
@@ -357,6 +358,11 @@ public class SizeCompatTests extends WindowTestsBase {
         final WindowState window = createWindow(null, TYPE_BASE_APPLICATION, mActivity, "window");
 
         assertEquals(window, mActivity.findMainWindow());
+
+        spyOn(mActivity.mLetterboxUiController);
+        doReturn(true).when(mActivity.mLetterboxUiController)
+                .isSurfaceReadyAndVisible(any());
+
         assertTrue(mActivity.mLetterboxUiController.shouldShowLetterboxUi(
                 mActivity.findMainWindow()));