Polish the transition when unlocking to home

- Only take snapshot if keyguard is secure because the snapshot
  doesn't help too much if there is unlocking window animation,
  because screen is already turned on in this case.
- Only use the snapshot when unlocking to home directly because
  the visual look may be worse with translate animation.
- Dismiss the snapshot starting window directly when the main
  window is ready, so it has less chance to see the fading
  translucent outdated snapshot.

Bug: 140811348
Bug: 148553119
Test: Unlock device with fingerprint and password.
      Check the top area of home doesn't have obvious
      fading scrim.

Change-Id: Ifb1302bd185d83ca9b203cf5d01a8f50fa1d6e69

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

@@ -1723,10 +1723,9 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
                 // The snapshot of home is only used once because it won't be updated while screen
                 // is on (see {@link TaskSnapshotController#screenTurningOff}).
                 mWmService.mTaskSnapshotController.removeSnapshotCache(task.mTaskId);
-                // TODO(b/9684093): Use more general condition to specify the case.
-                if (mDisplayContent.mAppTransition
-                        .getAppTransition() != WindowManager.TRANSIT_KEYGUARD_GOING_AWAY) {
-                    // Only use snapshot of home as starting window when unlocking.
+                if ((mDisplayContent.mAppTransition.getTransitFlags()
+                        & WindowManager.TRANSIT_FLAG_KEYGUARD_GOING_AWAY_NO_ANIMATION) == 0) {
+                    // Only use snapshot of home as starting window when unlocking directly.
                     return false;
                 }
             }

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

@@ -1183,6 +1183,11 @@ public class DisplayPolicy {
 
         if (transit == TRANSIT_PREVIEW_DONE) {
             if (win.hasAppShownWindows()) {
+                if (win.isActivityTypeHome()) {
+                    // Dismiss the starting window as soon as possible to avoid the crossfade out
+                    // with old content because home is easier to have different UI states.
+                    return ANIMATION_NONE;
+                }
                 if (DEBUG_ANIM) Slog.i(TAG, "**** STARTING EXIT");
                 return R.anim.app_starting_exit;
             }

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

@@ -559,8 +559,10 @@ class TaskSnapshotController {
                         }
                     });
                     // Allow taking snapshot of home when turning screen off to reduce the delay of
-                    // unlocking/waking to home.
-                    snapshotTasks(mTmpTasks, true /* allowSnapshotHome */);
+                    // waking from secure lock to home.
+                    final boolean allowSnapshotHome =
+                            mService.mPolicy.isKeyguardSecure(mService.mCurrentUserId);
+                    snapshotTasks(mTmpTasks, allowSnapshotHome);
                 }
             } finally {
                 listener.onScreenOff();