update: how to compile native library and new win dll

README.md

@@ -36,4 +36,67 @@ if you use maven, you can put it `${project.basedir}/libs`, and edit config file
 </dependency>
 ```
 
-The usage of api, you can see example cases in `src/main/java/example`.
+The usage of api, you can see example cases in `src/main/java/example`.
+
+
+
+## Compiling the native library
+
+download source code of [webp project of Luciad](https://bitbucket.org/luciad/webp-imageio) , and unzip it.
+
+```shell
+wget https://bitbucket.org/luciad/webp-imageio/get/873c5677244b.zip -O luciad-webp-imageio-873c5677244b.zip
+unzip luciad-webp-imageio-873c5677244b.zip
+```
+
+download source code of [google webp project](https://chromium.googlesource.com/webm/libwebp)
+
+```shell
+git clone https://chromium.googlesource.com/webm/libwebp
+```
+
+or use the [mirror repo](https://github.com/webmproject/libwebp) 
+
+copy folder libwebp into folder luciad-webp-imageio-873c5677244b, and create a directory called `build` in the  folder luciad-webp-imageio-873c5677244b
+
+folder tree like this:
+
+```
+luciad-webp-imageio-873c5677244b/
+	|_ build/	<-- just created 
+	|_ gradle/
+	|_ src/
+	|_ libwebp/  <-- copy from project libwebp 
+	|_ .hgignore
+	|....
+	|.... (other files)
+```
+
+Install CMake 2.8 or newer. CMake can be downloaded from [www.cmake.org](http://www.cmake.org/) or installed using your systems package manager. if you use Win10 and VS 2019, it need CMake 3.14 or newer.
+
+Open a terminal and navigate to the newly created 'build' directory. 
+
+```
+cd ./build
+cmake ..
+cmake --build .
+```
+
+The compiled library can be found under the directory `build/src/main/c`
+
+if you need specific the generator-name, please add `-G <generator-name>` parameter for cmake, like this
+
+```shell
+// cmake ..
+cmake .. -G "Visual Studio 16 2019"
+```
+
+
+
+## Compiling the Java library
+
+- Run `./gradlew build -x test` in the root of the project
+- The compiled Java library can be found under the `build` directory
+
+
+