Fix. Issue: #853. More flexible way to detect and use existing Zlib libraries. Thanks Daniel for providing this patch.

CMakeLists.txt

@@ -70,21 +70,29 @@ if( MSVC )
 		set(OUT_OF_SOURCE 1)
 	endif()
 	
-    if ( NOT EXPAT_LIBRARY  )
     # link dependent libraries
+    if ( NOT EXPAT_LIBRARY  )
     	if (OUT_OF_SOURCE)
     		set(EXPAT_LIBRARY      ../../../${E}/$(ConfigurationName)/expat)
-    		set(ZLIB_LIBRARY       ../../../${Z}/$(ConfigurationName)/zlib )
-    		set(EXPAT_INCLUDE_DIR  ../${E}/lib )
-    		set(ZLIB_INCLUDE_DIR   ../${Z}     )
+    		set(EXPAT_INCLUDE_DIR  ../${E}/lib)
 		else()
     		set(EXPAT_LIBRARY      ../../${E}/$(ConfigurationName)/expat)
+    		set(EXPAT_INCLUDE_DIR  ../${E}/lib)
+    	endif()
+    	include_directories( ${EXPAT_INCLUDE_DIR} msvc64\\include src\\include)
+	endif()
+	
+	FIND_PACKAGE(ZLIB QUIET)
+    if ( NOT ZLIB_FOUND )
+        if (OUT_OF_SOURCE)
+            set(ZLIB_LIBRARY       ../../../${Z}/$(ConfigurationName)/zlib )
+            set(ZLIB_INCLUDE_DIR   ../${Z})
+        else()
             set(ZLIB_LIBRARY       ../../${Z}/$(ConfigurationName)/zlib)
-    		set(EXPAT_INCLUDE_DIR  ../${E}/lib )
-    		set(ZLIB_INCLUDE_DIR   ../${Z}     )
+            set(ZLIB_INCLUDE_DIR   ../${Z})
         endif()
-    	include_directories( ${EXPAT_INCLUDE_DIR} ${ZLIB_INCLUDE_DIR} msvc64\\include src\\include)
     endif()
+    include_directories(${ZLIB_INCLUDE_DIR})
 	
 	if ( EXIV2_ENABLE_SHARED )
 	    add_library(${E} SHARED IMPORTED)

README-CMAKE

@@ -214,6 +214,12 @@ Specify the location of the prebuilt libraries on the cmake command line:
 For example:
 cmake -G "NMake Makefiles" .. -DEXPAT_LIBRARY=%KDE4_INSTALL_DIR%/lib/libexpat.lib
 
+Daniel has provided a patch (SVN:2893) which enables you to specify a ZLIB search path:
+Example:
+   cmake.exe -G "Visual Studio 11 Win64" -DZLIB_ROOT=..\zlib-1.2.7-dev;..\zlib-1.2.7-dev\Release ...
+   
+If ZLIB is not located on the path provided, the normal default (..\zlib-1.2.7) will be used.
+
 ToDo: More information about parameters -DEXPAT_LIBRARTY -DZLIB_LIBRARY etc.
 
 4 Building and Installing for other users (Xcode, Eclipse, Qt)