Support PDF highlight annotation with opacity.

core/fpdfdoc/cpvt_generateap.cpp

Index: core/fpdfdoc/cpvt_generateap.cpp
diff --git a/core/fpdfdoc/cpvt_generateap.cpp b/core/fpdfdoc/cpvt_generateap.cpp
index 56b661271702cb5e3f6ad2c75f6ccad1b58d056a..13ef5061580a90beefb2cc89a169a34a74c25e04 100644
--- a/core/fpdfdoc/cpvt_generateap.cpp
+++ b/core/fpdfdoc/cpvt_generateap.cpp
@@ -538,8 +538,11 @@ bool CPVT_GenerateAP::GenerateHighlightAP(CPDF_Document* pDoc,
 
   CPDF_Dictionary* pGSDict = new CPDF_Dictionary;
   pGSDict->SetAtString("Type", "ExtGState");
-  pGSDict->SetAtNumber("ca", 1);
-  pGSDict->SetAtNumber("CA", 1);
+
+  FX_FLOAT fOpacity =
+      pAnnotDict->KeyExist("CA") ? pAnnotDict->GetNumberBy("CA") : 1;
+  pGSDict->SetAtNumber("ca", fOpacity);
+  pGSDict->SetAtNumber("CA", fOpacity);
   pGSDict->SetAtBoolean("AIS", false);
   pGSDict->SetAtString("BM", "Multiply");