Optimize alpha handling for stack scroller

Use a layer when an alpha is set. Currently, this breaks shadows
when alpha != 1f, however, b/15860114 will fix this.

Change-Id: I094d5896a5433ba9a0ecc17549ef2944f6b7881e

2 files changed, 16 insertions, 6 deletions

diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java b/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java
index b80a33b..1932843 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java
@@ -937,12 +937,16 @@ public class NotificationPanelView extends PanelView implements
     }
     private void updateNotificationTranslucency() {
         float alpha = (getNotificationsTopY() + mNotificationStackScroller.getItemHeight())
-                / (mQsMinExpansionHeight + mNotificationStackScroller.getItemHeight() / 2);
+                / (mQsMinExpansionHeight + mNotificationStackScroller.getBottomStackPeekSize()
+                        + mNotificationStackScroller.getCollapseSecondCardPadding());
         alpha = Math.max(0, Math.min(alpha, 1));
         alpha = (float) Math.pow(alpha, 0.75);
-
-        // TODO: Draw a rect with DST_OUT over the notifications to achieve the same effect -
-        // this would be much more efficient.
+        if (alpha != 1f && mNotificationStackScroller.getLayerType() != LAYER_TYPE_HARDWARE) {
+            mNotificationStackScroller.setLayerType(LAYER_TYPE_HARDWARE, null);
+        } else if (alpha == 1f
+                && mNotificationStackScroller.getLayerType() == LAYER_TYPE_HARDWARE) {
+            mNotificationStackScroller.setLayerType(LAYER_TYPE_NONE, null);
+        }
         mNotificationStackScroller.setAlpha(alpha);
     }
 
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/stack/NotificationStackScrollLayout.java b/packages/SystemUI/src/com/android/systemui/statusbar/stack/NotificationStackScrollLayout.java
index 9b819f2..e0167e9 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/stack/NotificationStackScrollLayout.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/stack/NotificationStackScrollLayout.java
@@ -470,6 +470,10 @@ public class NotificationStackScrollLayout extends ViewGroup
         return mBottomStackPeekSize;
     }
 
+    public int getCollapseSecondCardPadding() {
+        return mCollapseSecondCardPadding;
+    }
+
     public void setLongPressListener(SwipeHelper.LongPressListener listener) {
         mSwipeHelper.setLongPressListener(listener);
         mLongPressListener = listener;
@@ -1955,8 +1959,10 @@ public class NotificationStackScrollLayout extends ViewGroup
     }
 
     public void setScrimAlpha(float progress) {
-        mAmbientState.setScrimAmount(progress);
-        requestChildrenUpdate();
+        if (progress != mAmbientState.getScrimAmount()) {
+            mAmbientState.setScrimAmount(progress);
+            requestChildrenUpdate();
+        }
     }
 
     /**