hwc: Add support for plane alpha

HWC 1.2 API passes down the plane alpha and the blending
operation to apply. Pass this information to the MDP.

Change-Id: I7fbd17345d9157aa654e4b1031ac3e26adf87f37
diff --git a/liboverlay/overlayUtils.h b/liboverlay/overlayUtils.h
index b543018..e49a50c 100644
--- a/liboverlay/overlayUtils.h
+++ b/liboverlay/overlayUtils.h
@@ -212,6 +212,8 @@
 
 enum { MAX_PATH_LEN = 256 };
 
+enum { DEFAULT_PLANE_ALPHA = 0xFF };
+
 /**
  * Rotator flags: not to be confused with orientation flags.
  * Usually, you want to open the rotator to make sure it is
@@ -329,21 +331,36 @@
     OVERLAY_TRANSFORM_INV = 0x80
 };
 
+enum eBlending {
+    OVERLAY_BLENDING_UNDEFINED = 0x0,
+    /* No blending */
+    OVERLAY_BLENDING_OPAQUE,
+    /* src.rgb + dst.rgb*(1-src_alpha) */
+    OVERLAY_BLENDING_PREMULT,
+    /* src.rgb * src_alpha + dst.rgb (1 - src_alpha) */
+    OVERLAY_BLENDING_COVERAGE,
+};
+
 // Used to consolidate pipe params
 struct PipeArgs {
     PipeArgs() : mdpFlags(OV_MDP_FLAGS_NONE),
         zorder(Z_SYSTEM_ALLOC),
         isFg(IS_FG_OFF),
-        rotFlags(ROT_FLAGS_NONE){
+        rotFlags(ROT_FLAGS_NONE),
+        planeAlpha(DEFAULT_PLANE_ALPHA),
+        blending(OVERLAY_BLENDING_COVERAGE){
     }
 
     PipeArgs(eMdpFlags f, Whf _whf,
-            eZorder z, eIsFg fg, eRotFlags r) :
+            eZorder z, eIsFg fg, eRotFlags r,
+            int pA = DEFAULT_PLANE_ALPHA, eBlending b = OVERLAY_BLENDING_COVERAGE) :
         mdpFlags(f),
         whf(_whf),
         zorder(z),
         isFg(fg),
-        rotFlags(r) {
+        rotFlags(r),
+        planeAlpha(pA),
+        blending(b){
     }
 
     eMdpFlags mdpFlags; // for mdp_overlay flags
@@ -351,6 +368,8 @@
     eZorder zorder; // stage number
     eIsFg isFg; // control alpha & transp
     eRotFlags rotFlags;
+    int planeAlpha;
+    eBlending blending;
 };
 
 // Cannot use HW_OVERLAY_MAGNIFICATION_LIMIT, since at the time