Made zlib an optional dependency.

Only needed to read legacy files, which is not fully supported yet.  Hopefully
this will make it easier to build on Windows.

CMakeLists.txt

@@ -48,11 +48,11 @@ if (MINGW)
    set (QT_BIN_DIR ${QT_BASE_DIR}/bin)
 endif ()
 
-find_package (ZLIB 1.2 REQUIRED)
 
 #
 # Optional dependencies
 #
+find_package (ZLIB 1.2 QUIET)
 find_package (GnuBarcode 0.98 QUIET)
 find_package (LibQrencode 3.4 QUIET)
 find_package (LibZint 2.6 QUIET)
@@ -91,7 +91,12 @@ message (STATUS "Installation prefix ..... " ${CMAKE_INSTALL_PREFIX})
 message (STATUS "Source code location .... " ${glabels_SOURCE_DIR})
 message (STATUS "C++ Compiler ............ " ${CMAKE_CXX_COMPILER_ID} " " ${CMAKE_CXX_COMPILER} " " ${CMAKE_CXX_COMPILER_VERSION})
 message (STATUS "Qt version .............. " ${Qt5Core_VERSION})
-message (STATUS "zlib version ............ " ${ZLIB_VERSION_STRING})
+
+if (ZLIB_FOUND)
+  message (STATUS "zlib (optional).......... " ${ZLIB_VERSION_STRING})
+else (ZLIB_FOUND)
+  message (STATUS "zlib (optional).......... No.")
+endif (ZLIB_FOUND)
 
 if (GNUBARCODE_FOUND)
   message (STATUS "GNU Barcode (optional)... " ${GNUBARCODE_VERSION_STRING})

model/CMakeLists.txt

@@ -1,5 +1,15 @@
 project (Model LANGUAGES CXX)
 
+#=======================================
+# Handle optional dependencies
+#=======================================
+if (${ZLIB_FOUND})
+  add_definitions (-DHAVE_ZLIB=1)
+  set (OPTIONAL_ZLIB ZLIB::ZLIB)
+else ()
+  set (OPTIONAL_ZLIB "")
+endif ()
+
 #=======================================
 # Sources
 #=======================================
@@ -96,7 +106,7 @@ target_link_libraries (Model
   Qt5::PrintSupport
   Qt5::Xml
   Qt5::Svg
-  ZLIB::ZLIB
+  ${OPTIONAL_ZLIB}
 )
 
 #=======================================

model/XmlLabelParser.cpp

@@ -41,8 +41,9 @@
 #include <QTextDocument>
 #include <QtDebug>
 
+#if HAVE_ZLIB
 #include <zlib.h>
-
+#endif
 
 namespace glabels
 {
@@ -70,10 +71,15 @@ namespace glabels
 			QByteArray rawData = file.readAll();
 			if ( ((rawData[0]&0xFF) == 0x1F) && ((rawData[1]&0xFF) == 0x8b) ) // gzip magic number 0x1F, 0x8B
 			{
+#if HAVE_ZLIB
 				// gzip compressed format
 				QByteArray unzippedData;
 				gunzip( rawData, unzippedData );
 				success = doc.setContent( unzippedData, false, &errorString, &errorLine, &errorColumn );
+#else
+				qWarning() << "Warning: Cannot read compressed glabels project file!  gLabels not build with ZLIB.";
+				return nullptr;
+#endif
 			}
 			else
 			{
@@ -175,6 +181,7 @@ namespace glabels
 		}
 
 
+#if HAVE_ZLIB
 		void
 		XmlLabelParser::gunzip( const QByteArray& data, QByteArray& result )
 		{
@@ -223,7 +230,8 @@ namespace glabels
 			// clean up
 			inflateEnd(&strm);
 		}
-
+#endif
+		
 
 		Model*
 		XmlLabelParser::parseRootNode( const QDomElement &node )