clamp & round alpha

 Bug: 16842521

Change-Id: Ifd93f40b5751746835c9d56bb3c2b5ba700bdccc
diff --git a/libs/hwui/RenderProperties.h b/libs/hwui/RenderProperties.h
index 9898bde..41f48cd 100644
--- a/libs/hwui/RenderProperties.h
+++ b/libs/hwui/RenderProperties.h
@@ -209,7 +209,7 @@
     }
 
     bool setAlpha(float alpha) {
-        alpha = fminf(1.0f, fmaxf(0.0f, alpha));
+        alpha = MathUtils::clampAlpha(alpha);
         return RP_SET(mPrimitiveFields.mAlpha, alpha);
     }