Adds Dockerfile. Updates Makefile and README.

This commit adds a Dockerfile which allows to build GoCV Docker images
to build GoCV programs that can be run in Docker containers.

A new make target was added to the Makefile to build Docker image
easily. Makefile now correctly sets cmake BUILD parameters, too.

Finally, README has been updated with the information about how to build
Docker images.

.dockerignore

@@ -0,0 +1 @@
+**

Dockerfile

@@ -0,0 +1,60 @@
+FROM ubuntu:16.04 AS opencv
+LABEL maintainer="Hybridgroup"
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+            git build-essential cmake pkg-config unzip libgtk2.0-dev \
+            curl ca-certificates libcurl4-openssl-dev libssl-dev \
+            libavcodec-dev libavformat-dev libswscale-dev libtbb2 libtbb-dev \
+            libjpeg-dev libpng-dev libtiff-dev libdc1394-22-dev && \
+            rm -rf /var/lib/apt/lists/*
+
+ARG OPENCV_VERSION="4.0.0"
+ENV OPENCV_VERSION $OPENCV_VERSION
+
+RUN curl -Lo opencv.zip https://github.com/opencv/opencv/archive/${OPENCV_VERSION}.zip && \
+            unzip -q opencv.zip && \
+            curl -Lo opencv_contrib.zip https://github.com/opencv/opencv_contrib/archive/${OPENCV_VERSION}.zip && \
+            unzip -q opencv_contrib.zip && \
+            rm opencv.zip opencv_contrib.zip && \
+            cd opencv-${OPENCV_VERSION} && \
+            mkdir build && cd build && \
+            cmake -D CMAKE_BUILD_TYPE=RELEASE \
+                  -D CMAKE_INSTALL_PREFIX=/usr/local \
+                  -D OPENCV_EXTRA_MODULES_PATH=../../opencv_contrib-${OPENCV_VERSION}/modules \
+                  -D WITH_JASPER=OFF \
+                  -D BUILD_DOCS=OFF \
+                  -D BUILD_EXAMPLES=OFF \
+                  -D BUILD_TESTS=OFF \
+                  -D BUILD_PERF_TESTS=OFF \
+                  -D BUILD_opencv_java=NO \
+                  -D BUILD_opencv_python=NO \
+                  -D BUILD_opencv_python2=NO \
+                  -D BUILD_opencv_python3=NO \
+                  -D OPENCV_GENERATE_PKGCONFIG=ON .. && \
+            make -j $(nproc --all) && \
+            make preinstall && make install && ldconfig && \
+            cd / && rm -rf opencv*
+
+#################
+#  Go + OpenCV  #
+#################
+FROM opencv AS gocv
+LABEL maintainer="Hybridgroup"
+
+ARG GOVERSION="1.11.2"
+ENV GOVERSION $GOVERSION
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+            git software-properties-common && \
+            curl -Lo go${GOVERSION}.linux-amd64.tar.gz https://dl.google.com/go/go${GOVERSION}.linux-amd64.tar.gz && \
+            tar -C /usr/local -xzf go${GOVERSION}.linux-amd64.tar.gz && \
+            rm go${GOVERSION}.linux-amd64.tar.gz && \
+            rm -rf /var/lib/apt/lists/*
+
+ENV GOPATH /go
+ENV PATH $GOPATH/bin:/usr/local/go/bin:$PATH
+
+RUN mkdir -p "$GOPATH/src" "$GOPATH/bin" && chmod -R 777 "$GOPATH"
+WORKDIR $GOPATH
+
+RUN go get -u -d gocv.io/x/gocv && go run ${GOPATH}/src/gocv.io/x/gocv/cmd/version/main.go

Makefile

@@ -1,9 +1,12 @@
 .ONESHELL:
-.PHONY: test deps download build clean astyle cmds
+.PHONY: test deps download build clean astyle cmds docker
 
 # OpenCV version to use.
 OPENCV_VERSION?=4.0.0
 
+# Go version to use when building Docker image
+GOVERSION?=1.11.2
+
 # Temporary directory to put files into.
 TMP_DIR?=/tmp/
 
@@ -56,7 +59,7 @@ build:
 	cd $(TMP_DIR)opencv/opencv-$(OPENCV_VERSION)
 	mkdir build
 	cd build
-	cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D OPENCV_EXTRA_MODULES_PATH=$(TMP_DIR)opencv/opencv_contrib-$(OPENCV_VERSION)/modules -D BUILD_DOCS=OFF BUILD_EXAMPLES=OFF -D BUILD_TESTS=OFF -D BUILD_PERF_TESTS=OFF -D BUILD_opencv_java=OFF -D BUILD_opencv_python=OFF -D BUILD_opencv_python2=OFF -D BUILD_opencv_python3=OFF WITH_JASPER=OFF -DOPENCV_GENERATE_PKGCONFIG=ON ..
+	cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D OPENCV_EXTRA_MODULES_PATH=$(TMP_DIR)opencv/opencv_contrib-$(OPENCV_VERSION)/modules -D BUILD_DOCS=OFF -D BUILD_EXAMPLES=OFF -D BUILD_TESTS=OFF -D BUILD_PERF_TESTS=OFF -D BUILD_opencv_java=NO -D BUILD_opencv_python=NO -D BUILD_opencv_python2=NO -D BUILD_opencv_python3=NO -D WITH_JASPER=OFF -DOPENCV_GENERATE_PKGCONFIG=ON ..
 	$(MAKE) -j $(shell nproc --all)
 	$(MAKE) preinstall
 	cd -
@@ -66,7 +69,7 @@ build_raspi:
 	cd $(TMP_DIR)opencv/opencv-$(OPENCV_VERSION)
 	mkdir build
 	cd build
-	cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D OPENCV_EXTRA_MODULES_PATH=$(TMP_DIR)opencv/opencv_contrib-$(OPENCV_VERSION)/modules -D BUILD_DOCS=OFF BUILD_EXAMPLES=OFF -D BUILD_TESTS=OFF -D BUILD_PERF_TESTS=OFF -D BUILD_opencv_java=OFF -D BUILD_opencv_python=OFF -D BUILD_opencv_python2=OFF -D BUILD_opencv_python3=OFF -D ENABLE_NEON=ON -D ENABLE_VFPV3=ON WITH_JASPER=OFF -DOPENCV_GENERATE_PKGCONFIG=ON ..
+	cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D OPENCV_EXTRA_MODULES_PATH=$(TMP_DIR)opencv/opencv_contrib-$(OPENCV_VERSION)/modules -D BUILD_DOCS=OFF -D BUILD_EXAMPLES=OFF -D BUILD_TESTS=OFF -D BUILD_PERF_TESTS=OFF -D BUILD_opencv_java=OFF -D BUILD_opencv_python=NO -D BUILD_opencv_python2=NO -D BUILD_opencv_python3=NO -D ENABLE_NEON=ON -D ENABLE_VFPV3=ON -D WITH_JASPER=OFF -D OPENCV_GENERATE_PKGCONFIG=ON ..
 	$(MAKE) -j $(shell nproc --all)
 	$(MAKE) preinstall
 	cd -
@@ -98,6 +101,8 @@ verify:
 test:
 	go test . ./contrib
 
+docker:
+	docker build --build-arg OPENCV_VERSION=$(OPENCV_VERSION) --build-arg GOVERSION=$(GOVERSION) .
 
 astyle:
 	astyle --project=.astylerc --recursive *.cpp,*.h

README.md

@@ -223,6 +223,56 @@ Please note that you will need to run these 2 lines of code one time in your cur
 
 	go run -tags customenv ./cmd/version/main.go
 
+### Docker
+
+The project now provides `Dockerfile` which lets you build [GoCV](https://gocv.io/) Docker image which you can then use to build and run `GoCV` applications in Docker containers. The `Makefile` contains `docker` target which lets you build Docker image with a single command:
+
+```
+make docker
+```
+
+By default Docker image built by running the command above ships [Go](https://golang.org/) version `1.11.2`, but if you would like to build an image which uses different version of `Go` you can override the default value when running the target command:
+
+```
+make docker GOVERSION='1.11.1'
+```
+
+#### Running GUI programs in Docker on macOS
+
+Sometimes your `GoCV` programs create graphical interfaces like windows eg. when you use `gocv.Window` type when you display an image or video stream. Running the programs which create graphical interfaces in Docker container on macOS is unfortunately a bit elaborate, but not impossible. First you need to satisfy the following prerequisites:
+* install [xquartz](https://www.xquartz.org/). You can also install xquartz using [homebrew](https://brew.sh/) by running `brew install cask xquartz`
+* install [socat](https://linux.die.net/man/1/socat) `brew install socat`
+
+Note, you will have to log out and log back in to your machine once you have installed `xquartz`. This is so the X window system is reloaded.
+
+Once you have installed all the prerequisites you need to allow connections from network clients to `xquartz`. Here is how you do that. First run the following command to open `xquart` so you can configure it:
+
+```shell
+open -a xquartz
+```
+Click on *Security* tab in preferences and check the "Allow connections" box:
+
+![app image](./images/xquartz.png)
+
+Next, you need to create a TCP proxy using `socat` which will stream [X Window](https://en.wikipedia.org/wiki/X_Window_System) data into `xquart`. Before you start the proxy you need to make sure that there is no process listening in port `6000`. The following command should **not** return any results:
+
+```shell
+lsof -i TCP:6000
+```
+Now you can start a local proxy which will proxy the X Window traffic into xquartz which acts a your local X server:
+
+```shell
+socat TCP-LISTEN:6000,reuseaddr,fork UNIX-CLIENT:\"$DISPLAY\"
+```
+
+You are now finally ready to run your `GoCV` GUI programs in Docker containers. In order to make everything work you must set `DISPLAY` environment variables as shown in a sample command below:
+
+```shell
+docker run -it --rm -e DISPLAY=docker.for.mac.host.internal:0 your-gocv-app
+```
+
+**Note, since Docker for MacOS does not provide any video device support, you won't be able run GoCV apps which require camera.**
+
 ### Alpine 3.7 Docker image
 
 There is a Docker image with Alpine 3.7 that has been created by project contributor [@denismakogon](https://github.com/denismakogon). You can find it located at [https://github.com/denismakogon/gocv-alpine](https://github.com/denismakogon/gocv-alpine).
@@ -266,7 +316,7 @@ This new Homebrew recipe will install only OpenCV 4.0.0 without all of the Pytho
 ### pkgconfig Installation
 pkg-config is used to determine the correct flags for compiling and linking OpenCV.
 You can install it by using Homebrew:
-    
+
     brew install pkgconfig
 
 ### Verifying the installation
@@ -402,7 +452,7 @@ You can get the profile's count at any time using:
 gocv.MatProfile.Count()
 ```
 
-You can display the current entries (the stack traces) with: 
+You can display the current entries (the stack traces) with:
 
 ```go
 var b bytes.Buffer