Update README and documentation

Instructions to include external library into a widget

Change-Id: Ic5c8c477fdbc1d374f1f88260b51cb9f200d02e1
Signed-off-by: Romain Forlot <romain.forlot@iot.bzh>

1 files changed, 72 insertions, 8 deletions

diff --git a/docs/dev_guide/3_advanced_usage.md b/docs/dev_guide/3_advanced_usage.md
index f9d9e90..ae8d1ec 100644
--- a/docs/dev_guide/3_advanced_usage.md
+++ b/docs/dev_guide/3_advanced_usage.md
@@ -30,20 +30,27 @@ application, macros make the difference using ***LABELS*** property.
 Choose between:
 
 - **BINDING**: Shared library that be loaded by the AGL Application Framework
-- **BINDINGV2**: Shared library that be loaded by the AGL Application Framework.
- This has to be accompagnied with a JSON file named like the *${OUTPUT_NAME}-apidef* of
- the target that describe the API with OpenAPI syntax (e.g: *mybinding-apidef*).
- Or you can choose the name by setting the *CACHE* cmake variable *OPENAPI_DEF*
- (***CAUTION***: setting a CACHE variable is needed, or set a normal variable
- with the *PARENT_SCOPE* option to make it visible for the parent scope
- where the target is defined) JSON file will be used to generate header file
- using `afb-genskel` tool.
+- **BINDINGV2**: Shared library that be loaded by the AGL Application Framework
+ This has to be accompagnied with a JSON file named like the
+ *${OUTPUT_NAME}-apidef* of the target that describe the API with OpenAPI
+ syntax (e.g: *mybinding-apidef*). Or you can choose the name, without the
+ extension, by setting the *CACHE* cmake variable *OPENAPI_DEF* (***CAUTION***:
+ setting a CACHE variable is needed, or set a normal variable with the
+ *PARENT_SCOPE* option to make it visible for the parent scope where the target
+ is defined) JSON file will be used to generate header file using `afb-genskel`
+ tool.
+- **PLUGIN**: Shared library meant to be used as a binding plugin. Binding
+ would load it as a plugin to extend its functionnalities. It should be named
+ with a special extension that you choose with SUFFIX cmake target property or
+ it'd be **.ctlso** by default.
 - **HTDOCS**: Root directory of a web app. This target has to build its
  directory and puts its files in the ${CMAKE_CURRENT_BINARY_DIR}/${TARGET_NAME}
 - **DATA**: Resources used by your application. This target has to build its
  directory and puts its files in the ${CMAKE_CURRENT_BINARY_DIR}/${TARGET_NAME}
 - **EXECUTABLE**: Entry point of your application executed by the AGL
  Application Framework
+- **LIBRARY**: An external 3rd party library bundled with the binding for its
+ own purpose because platform doesn't provide it.
 
 > **TIP** you should use the prefix _afb-_ with your **BINDING* targets which
 > stand for **Application Framework Binding**.
@@ -61,6 +68,63 @@ SET_TARGET_PROPERTIES(${TARGET_NAME} PROPERTIES
 > targets. This is already handle by template and will be installed in the
 > following path : **${CMAKE_INSTALL_PREFIX}/${PROJECT_NAME}**
 
+## Add external 3rd party library
+
+You could need to include an external library that isn't shipped in the
+platform. Then you have to bundle the required library in the `lib` widget
+directory.
+
+Templates includes some facilities to help you to do so. Classic way to do so
+is to declare as many CMake ExternalProject as library you need.
+
+An ExternalProject is a special CMake module that let you define how to:
+download, update, patch, configure, build and install an external project. It
+doesn't have to be a CMake project and custom step could be added for special
+needs using ExternalProject step. More informations on CMake [ExternalProject
+documentation site](https://cmake.org/cmake/help/v3.5/module/ExternalProject.html?highlight=externalproject).
+
+Example to include `mxml` library for [unicens2-binding](https://github.com/iotbzh/unicens2-binding)
+project:
+
+```cmake
+set(MXML external-mxml)
+set(MXML_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/mxml)
+ExternalProject_Add(${MXML}
+    GIT_REPOSITORY https://github.com/michaelrsweet/mxml.git
+    GIT_TAG release-2.10
+    SOURCE_DIR ${MXML_SOURCE_DIR}
+    CONFIGURE_COMMAND ./configure --build x86_64 --host aarch64
+    BUILD_COMMAND make libmxml.so.1.5
+    BUILD_IN_SOURCE 1
+    INSTALL_COMMAND ""
+)
+
+PROJECT_TARGET_ADD(mxml)
+
+add_library(${TARGET_NAME} SHARED IMPORTED GLOBAL)
+
+SET_TARGET_PROPERTIES(${TARGET_NAME} PROPERTIES
+    LABELS LIBRARY
+    IMPORTED_LOCATION ${MXML_SOURCE_DIR}/libmxml.so.1
+    INTERFACE_INCLUDE_DIRECTORIES ${MXML_SOURCE_DIR}
+)
+
+add_dependencies(${TARGET_NAME} ${MXML})
+```
+
+Here we define an external project that drive the build of the library then we
+define new CMake target of type **IMPORTED**. Meaning that this target hasn't
+be built using CMake but is available at the location defined in the target
+property *IMPORTED_LOCATION*.
+
+Then target *LABELS* property is set to **LIBRARY** to ship it in the widget.
+
+Unicens project also need some header from this library, so we use the target
+property *INTERFACE_INCLUDE_DIRECTORIES*. Setting that when another target link
+to that imported target, it can access to the include directories.
+
+We bound the target to the external project using a CMake dependency at last.
+
 ## Macro reference
 
 ### PROJECT_TARGET_ADD