Some polishing for the cmake ReSVG discovery (#187)

* Search for libresvg.so in RESVGDIR also

This means that RESVGDIR can be pointed to the `target/release` dir 
where resvg was built, and both `libresvg.so` and `include/resvg.h` will 
be found.

* ReSVG: Fix up discovery module

`find_package_handle_standard_args` is supposed to set the `_FOUND` 
variable automatically (as the comment right above it says), as well as 
handling things like REQUIRED, QUIETLY, etc. It should always be run at 
the end of a module, for this reason.

This change removes the conditionals around the call, lets it handle 
what it's meant to handle, and defines a custom failure message for 
discovery that replaces the one in `src/CMakeList.txt`. 

In addition, the `REQRUIRED` is removed from `tests/CMakeLists.txt`, 
since it's _supposed_ to mark the module as required (which ReSVG is 
not), and was only working due to the aforementioned improper 
conditional wrapping of the module's cleanup.

* FindRESVG.cmake does not set RESVG_DEFINITIONS

Remove the comment that claims it does.

Author: ferdnyc

cmake/Modules/FindRESVG.cmake

@@ -3,7 +3,6 @@
 # RESVG_FOUND - System has RESVG
 # RESVG_INCLUDE_DIRS - The RESVG include directories
 # RESVG_LIBRARIES - The libraries needed to use RESVG
-# RESVG_DEFINITIONS - Compiler switches required for using RESVG
 find_path ( RESVG_INCLUDE_DIR ResvgQt.h
             PATHS ${RESVGDIR}/include/resvg
                   $ENV{RESVGDIR}/include/resvg
@@ -16,19 +15,14 @@ find_path ( RESVG_INCLUDE_DIR ResvgQt.h
 find_library ( RESVG_LIBRARY NAMES resvg
                PATHS /usr/lib
                     /usr/local/lib
+                    $ENV{RESVGDIR}
                     $ENV{RESVGDIR}/lib )
 
 set ( RESVG_LIBRARIES ${RESVG_LIBRARY} )
 set ( RESVG_INCLUDE_DIRS ${RESVG_INCLUDE_DIR} )
 
-SET( RESVG_FOUND FALSE )
-
-IF ( RESVG_INCLUDE_DIR AND RESVG_LIBRARY )
-    SET ( RESVG_FOUND TRUE )
-
-    include ( FindPackageHandleStandardArgs )
-    # handle the QUIETLY and REQUIRED arguments and set RESVG_FOUND to TRUE
-    # if all listed variables are TRUE
-    find_package_handle_standard_args ( RESVG DEFAULT_MSG RESVG_LIBRARY RESVG_INCLUDE_DIR )
-ENDIF ( RESVG_INCLUDE_DIR AND RESVG_LIBRARY )
-
+include ( FindPackageHandleStandardArgs )
+# handle the QUIETLY and REQUIRED arguments and set RESVG_FOUND to TRUE
+# if all listed variables are TRUE
+find_package_handle_standard_args ( RESVG "Could NOT find RESVG, using Qt SVG parsing instead" RESVG_LIBRARY RESVG_INCLUDE_DIR )
+mark_as_advanced( RESVG_LIBRARY RESVG_INCLUDE_DIR )

src/CMakeLists.txt

@@ -194,8 +194,6 @@ if (RESVG_FOUND)
    # define a global var (used in the C++)
    add_definitions( -DUSE_RESVG=1 )
    SET(CMAKE_SWIG_FLAGS "-DUSE_RESVG=1")
-else(RESVG_FOUND)
-	message("-- Could NOT find libresvg (using Qt SVG parsing instead)")
 endif(RESVG_FOUND)
 
 ################### JSONCPP #####################

tests/CMakeLists.txt

@@ -181,7 +181,7 @@ include_directories(${ZMQ_INCLUDE_DIRS})
 
 ################### RESVG #####################
 # Find resvg library (used for rendering svg files)
-FIND_PACKAGE(RESVG REQUIRED)
+FIND_PACKAGE(RESVG)
 
 # Include resvg headers (optional SVG library)
 if (RESVG_FOUND)