[CMake] add configuration dependend exports for plugin install dir.

add function to get the current plugin install dir

cmake/MapnikExport.cmake

@@ -1,6 +1,6 @@
 include(CMakePackageConfigHelpers)
 
-# set the cmake targets install location
+# export mapnik configuration
 write_basic_package_version_file(
     "${CMAKE_CURRENT_BINARY_DIR}/mapnikConfigVersion.cmake"
     VERSION ${PROJECT_VERSION}
@@ -22,6 +22,7 @@ install(
     DESTINATION ${MAPNIK_CMAKE_DIR}
 )
 
+# install our modules, so that the expected target names are found. 
 install(
     FILES 
         "${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindCairo.cmake" 
@@ -35,3 +36,21 @@ install(EXPORT MapnikTargets
     FILE mapnikTargets.cmake
     NAMESPACE mapnik::
 )
+
+
+# Create configuration dependend files for the plugin install dirs.
+# some package managers are using different paths per configuration.
+string(TOLOWER "${CMAKE_BUILD_TYPE}" _build_type)
+string(TOUPPER "${CMAKE_BUILD_TYPE}" _build_type_l)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/mapnikPlugins-${_build_type}.cmake.in "set(MAPNIK_PLUGINS_DIR_${_build_type_l} \"@PACKAGE_PLUGINS_INSTALL_DIR@\" CACHE STRING \"\")\n")
+include(CMakePackageConfigHelpers)
+configure_package_config_file(
+  ${CMAKE_CURRENT_BINARY_DIR}/mapnikPlugins-${_build_type}.cmake.in
+  ${CMAKE_CURRENT_BINARY_DIR}/mapnikPlugins-${_build_type}.cmake
+  PATH_VARS PLUGINS_INSTALL_DIR
+  INSTALL_DESTINATION ${MAPNIK_CMAKE_DIR}
+)
+install(
+  FILES ${CMAKE_CURRENT_BINARY_DIR}/MapnikPlugins-${_build_type}.cmake
+  DESTINATION ${MAPNIK_CMAKE_DIR}
+)

cmake/MapnikInstall.cmake

@@ -39,7 +39,7 @@ endfunction()
 # Install executables. These are available via COMPONENTS in find_package
 #
 function(mapnik_install_utility _target)
-    set(_target_name "MapnikUtility_${_target}_Targets")
+    set(_target_name "mapnikUtilityTargets_${_target}")
     install(TARGETS ${_target}
         EXPORT ${_target_name}
         INCLUDES DESTINATION ${MAPNIK_INCLUDE_DIR}

cmake/mapnikConfig.cmake.in

@@ -2,7 +2,6 @@
 
 set_and_check(MAPNIK_INCLUDE_DIR "@PACKAGE_MAPNIK_INCLUDE_DIR@" CACHE STRING "")
 set_and_check(MAPNIK_FONTS_DIR "@PACKAGE_FONTS_INSTALL_DIR@" CACHE STRING "")
-set(MAPNIK_PLUGINS_DIR "@PACKAGE_PLUGINS_INSTALL_DIR@" CACHE STRING "")
 
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_CURRENT_LIST_DIR}/Modules/")
 
@@ -17,5 +16,35 @@ foreach(_comp ${mapnik_FIND_COMPONENTS})
     set(mapnik_FOUND False)
     set(mapnik_NOT_FOUND_MESSAGE "Unsupported component: ${_comp}")
   endif()
-  include("${CMAKE_CURRENT_LIST_DIR}/MapnikUtility_${_comp}_Targets.cmake")
+  include("${CMAKE_CURRENT_LIST_DIR}/mapnikUtilityTargets_${_comp}.cmake")
 endforeach()
+
+
+get_filename_component(_plugin_dir "${CMAKE_CURRENT_LIST_FILE}" PATH)
+file(GLOB CONFIG_FILES "${_plugin_dir}/mapnikPlugins-*.cmake")
+foreach(f ${CONFIG_FILES})
+  include(${f})
+endforeach()
+
+function(mapnik_find_plugin_dir PLUGIN_DIR)
+    string(TOUPPER "${CMAKE_BUILD_TYPE}" _build_type_l)
+    set(_plugin_dir "${MAPNIK_PLUGINS_DIR_${_build_config}}")
+    # only release has more then one configuration
+    if(NOT _plugin_dir) 
+        set(_all_rel_cfgs RELEASE RELWITHDEBINFO MINSIZEREL)
+        list(FIND _all_rel_cfgs ${_build_config} _is_rel_cfg)
+        # check if the current configuration is a known release configuration
+        if(${_is_rel_cfg} GREATER_EQUAL 0)
+            foreach(_rel_cfg IN LISTS _all_rel_cfgs)
+                set(_plugin_dir "${MAPNIK_PLUGINS_DIR_${_rel_cfg}}")
+                if(_plugin_dir) 
+                    break()
+                endif()
+            endforeach()
+        endif()
+    endif()
+    if(NOT _plugin_dir)
+        message(WARNING "Could not find a plugin install dir for configuration ${_build_type_l}")
+    endif()
+    set(${PLUGIN_DIR} ${_plugin_dir} PARENT_SCOPE)
+endfunction()  

docs/cmake-usage.md

@@ -34,10 +34,16 @@ All targets:
 * `mapnik::wkt`: wkt support for libmapnik.
 
 All mapnik executables and targets are exported within `mapnikTargets.cmake`. 
-
-The plugin dir is available in the variable `MAPNIK_PLUGINS_DIR`. 
 The font path is is available in the variable `MAPNIK_FONTS_DIR`. 
 
+The install location of the plugins might be configuration dependent. 
+For each configuration there exists a variable `MAPNIK_PLUGINS_DIR_<CONFIGURATION>` where `<CONFIGURATION>` is one of `CMAKE_BUILD_TYPE` as upper case.
+There is a function exported which you can use to query the plugin dir for known typical configurations:
+```
+mapnik_find_plugin_dir(MAPNIK_PLUGINS_DIR)
+```
+`MAPNIK_PLUGINS_DIR` will contain then the plugin dir. If a path could not be found, a warning is printed.
+
 ## Recommendations
 
 If you target a specific platform, it is recommended to create a toolchain file and set all the options and library path that you would normally set via cmd line options.