Optimization of alpha with DisplayList properties
Some views (such as ImageView and TextView) handle non-opaque alpha
values directly. This was originally an optimization, but we can handle it faster
in many cases without this optimization when DisplayList properties are enabled.
Basically, if a view has non-overlapping rendering, we set the alpha value directly
on the renderer (the equivalent of setting it on the Paint object) and draw each
primitive with that alpha value. Doing it this way avoids re-creating DisplayLists
while getting the same speedup that onSetAlpha() used to get pre-DisplayList properties.
Change-Id: I0f7827f075d3b35093a882d4adbb300a1063c288
diff --git a/libs/hwui/Snapshot.h b/libs/hwui/Snapshot.h
index b2bc879..30b03fc 100644
--- a/libs/hwui/Snapshot.h
+++ b/libs/hwui/Snapshot.h
@@ -208,6 +208,17 @@
*/
Region* region;
+ /**
+ * Current alpha value. This value is 1 by default, but may be set by a DisplayList which
+ * has translucent rendering in a non-overlapping View. This value will be used by
+ * the renderer to set the alpha in the current color being used for ensuing drawing
+ * operations. The value is inherited by child snapshots because the same value should
+ * be applied to descendents of the current DisplayList (for example, a TextView contains
+ * the base alpha value which should be applied to the child DisplayLists used for drawing
+ * the actual text).
+ */
+ float alpha;
+
private:
void ensureClipRegion();
void copyClipRectFromRegion();