Using OpenCV with Eclipse (plugin CDT) {#tutorial_linux_eclipse}
======================================

Prerequisites
-------------
Two ways, one by forming a project directly, and another by CMake Prerequisites
1.  Having installed [Eclipse](http://www.eclipse.org/) in your workstation (only the CDT plugin for
    C/C++ is needed). You can follow the following steps:
    -   Go to the Eclipse site
    -   Download [Eclipse IDE for C/C++
        Developers](http://www.eclipse.org/downloads/packages/eclipse-ide-cc-developers/heliossr2) .
        Choose the link according to your workstation.
2.  Having installed OpenCV. If not yet, go @ref tutorial_linux_install "here".

Making a project
----------------

1.  Start Eclipse. Just run the executable that comes in the folder.
2.  Go to **File -\> New -\> C/C++ Project**

    ![image](images/a0.png)

3.  Choose a name for your project (i.e. DisplayImage). An **Empty Project** should be okay for this
    example.

    ![image](images/a1.png)

4.  Leave everything else by default. Press **Finish**.
5.  Your project (in this case DisplayImage) should appear in the **Project Navigator** (usually at
    the left side of your window).

    ![image](images/a3.png)

6.  Now, let's add a source file using OpenCV:
    -   Right click on **DisplayImage** (in the Navigator). **New -\> Folder** .

        ![image](images/a4.png)

    -   Name your folder **src** and then hit **Finish**
    -   Right click on your newly created **src** folder. Choose **New source file**:
    -   Call it **DisplayImage.cpp**. Hit **Finish**

        ![image](images/a7.png)

7.  So, now you have a project with a empty .cpp file. Let's fill it with some sample code (in other
    words, copy and paste the snippet below):
    @code{.cpp}
    #include <opencv2/opencv.hpp>

    using namespace cv;

    int main( int argc, char** argv )
    {
      Mat image;
      image = imread( argv[1], 1 );

      if( argc != 2 || !image.data )
        {
          printf( "No image data \n" );
          return -1;
        }

      namedWindow( "Display Image", WINDOW_AUTOSIZE );
      imshow( "Display Image", image );

      waitKey(0);

      return 0;
    }
    @endcode
8.  We are only missing one final step: To tell OpenCV where the OpenCV headers and libraries are.
    For this, do the following:

    -   Go to **Project--\>Properties**
    -   In **C/C++ Build**, click on **Settings**. At the right, choose the **Tool Settings** Tab.
        Here we will enter the headers and libraries info:
        -#  In **GCC C++ Compiler**, go to **Includes**. In **Include paths(-l)** you should
            include the path of the folder where opencv was installed. In our example, this is
            /usr/local/include/opencv.

            ![image](images/a9.png)

            @note If you do not know where your opencv files are, open the **Terminal** and type:
            @code{.bash}
            pkg-config --cflags opencv
            @endcode
            For instance, that command gave me this output:
            @code{.bash}
            -I/usr/local/include/opencv -I/usr/local/include
            @endcode

        -#  Now go to **GCC C++ Linker**,there you have to fill two spaces:

            First in **Library search path (-L)** you have to write the path to where the opencv libraries
            reside, in my case the path is: :

                /usr/local/lib

            Then in **Libraries(-l)** add the OpenCV libraries that you may need. Usually just the 3 first
            on the list below are enough (for simple applications) . In my case, I am putting all of them
            since I plan to use the whole bunch:

            opencv_core opencv_imgproc opencv_highgui opencv_ml opencv_video opencv_features2d
            opencv_calib3d opencv_objdetect opencv_contrib opencv_legacy opencv_flann

            ![image](images/a10.png)

            If you don't know where your libraries are (or you are just psychotic and want to make sure
            the path is fine), type in **Terminal**:
            @code{.bash}
            pkg-config --libs opencv
            @endcode
            My output (in case you want to check) was:
            @code{.bash}
            -L/usr/local/lib -lopencv_core -lopencv_imgproc -lopencv_highgui -lopencv_ml -lopencv_video -lopencv_features2d -lopencv_calib3d -lopencv_objdetect -lopencv_contrib -lopencv_legacy -lopencv_flann
            @endcode
            Now you are done. Click **OK**

-   Your project should be ready to be built. For this, go to **Project-\>Build all**

    In the Console you should get something like

    ![image](images/a12.png)

    If you check in your folder, there should be an executable there.

Running the executable
----------------------

So, now we have an executable ready to run. If we were to use the Terminal, we would probably do
something like:
@code{.bash}
cd <DisplayImage_directory>
cd src
./DisplayImage ../images/HappyLittleFish.png
@endcode
Assuming that the image to use as the argument would be located in
\<DisplayImage_directory\>/images/HappyLittleFish.png. We can still do this, but let's do it from
Eclipse:

1.  Go to **Run-\>Run Configurations**
2.  Under C/C++ Application you will see the name of your executable + Debug (if not, click over
    C/C++ Application a couple of times). Select the name (in this case **DisplayImage Debug**).
3.  Now, in the right side of the window, choose the **Arguments** Tab. Write the path of the image
    file we want to open (path relative to the workspace/DisplayImage folder). Let's use
    **HappyLittleFish.png**:

    ![image](images/a14.png)

4.  Click on the **Apply** button and then in Run. An OpenCV window should pop up with the fish
    image (or whatever you used).

    ![image](images/a15.jpg)

5.  Congratulations! You are ready to have fun with OpenCV using Eclipse.

### V2: Using CMake+OpenCV with Eclipse (plugin CDT)

Say you have or create a new file, *helloworld.cpp* in a directory called *foo*:
@code{.cpp}
#include <opencv2/opencv.hpp>
using namespace cv;

int main ( int argc, char **argv )
{
  Mat img(480, 640, CV_8U);
  putText(img, "Hello World!", Point( 200, 400 ), FONT_HERSHEY_SIMPLEX | FONT_ITALIC, 1.0, Scalar( 255, 255, 0 ));
  imshow("My Window", img);
  waitKey();
  return 0;
}
@endcode
1.  Create a build directory, say, under *foo*: mkdir /build. Then cd build.
2.  Put a `CmakeLists.txt` file in build:
@code{.bash}
PROJECT( helloworld_proj )
FIND_PACKAGE( OpenCV REQUIRED )
ADD_EXECUTABLE( helloworld helloworld.cxx )
TARGET_LINK_LIBRARIES( helloworld \f${OpenCV_LIBS} )
@endcode
1.  Run: cmake-gui .. and make sure you fill in where opencv was built.
2.  Then click configure and then generate. If it's OK, **quit cmake-gui**
3.  Run `make -j4` (the -j4 is optional, it just tells the compiler to build in 4 threads). Make
    sure it builds.
4.  Start eclipse. Put the workspace in some directory but **not** in foo or `foo\build`
5.  Right click in the Project Explorer section. Select Import And then open the C/C++ filter.
    Choose *Existing Code* as a Makefile Project.
6.  Name your project, say *helloworld*. Browse to the Existing Code location `foo\build` (where
    you ran your cmake-gui from). Select *Linux GCC* in the *"Toolchain for Indexer Settings"* and
    press *Finish*.
7.  Right click in the Project Explorer section. Select Properties. Under C/C++ Build, set the
    *build directory:* from something like `${workspace_loc:/helloworld}` to
    `${workspace_loc:/helloworld}/build` since that's where you are building to.

    -#  You can also optionally modify the Build command: from make to something like
        `make VERBOSE=1 -j4` which tells the compiler to produce detailed symbol files for debugging and
        also to compile in 4 parallel threads.

8.  Done!