Animate taskbar background alpha and visibility alpha

Setup codepath to animate the Taskbar when going to and from Launcher,
primarily by listening for pause/resume signals but also hints from
gesture nav and AppToOverviewAnimationProvider.

Additionally, add TaskbarStateHandler to listen for Launcher state
changes if Taskbar is enabled. Combined, the end behavior is:

- Background alpha is 0 when Launcher is resumed, and 1 when Launcher
  is paused (we can make this animation more interesting later).
- Taskbar is always visible when Launcher is paused, otherwise its
  visibility is determined by multiple factors: LauncherState and
  whether the IME is showing.

Bug: 171917176
Change-Id: I7856fc979931c9d12d714dee11d179fd1b5a6968

1 files changed, 5 insertions, 0 deletions

diff --git a/src/com/android/launcher3/states/SpringLoadedState.java b/src/com/android/launcher3/states/SpringLoadedState.java
index 45172b56ef..44bcc34588 100644
--- a/src/com/android/launcher3/states/SpringLoadedState.java
+++ b/src/com/android/launcher3/states/SpringLoadedState.java
@@ -90,4 +90,9 @@ public class SpringLoadedState extends LauncherState {
     public float getWorkspaceScrimAlpha(Launcher launcher) {
         return 0.3f;
     }
+
+    @Override
+    public int getVisibleElements(Launcher launcher) {
+        return super.getVisibleElements(launcher) & ~TASKBAR;
+    }
 }