Configure Qt and OpenCV On MacOSx

Introduction

This article shows how to use the QtCreator to build applications using the OpenCV library on MacOS.

Installing Qt

For installing Qt on mac, you first need to install xCode. Find it in the AppStore and install it. Then download the Qt installer from https://download.qt.io/archive/qt/. Execute it and voilà it is installed.

Installing OpenCV

First you need to install brew, type in a terminal:

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
brew update
echo "# Homebrew" >> ~/.bash_profile
echo "export PATH=/usr/local/bin:$PATH" >> ~/.bash_profile
source ~/.bash_profile

Then install OpenCV: brew install opencv

Configuring Qt

For Mac, the configuration is a little bit different, you need first to add some paths to the Qt creator builder

Open the Qt creator
Open your project
In the side left panel, click on the "Projects" button
In the second left side panel click on the "Build" button
Go to the "Build Environment" and click on "Details".
Open a terminal and type: 
	`which pkg-config`
If the command return nothing tape: 
	`brew install pkg-config`
else it will return a path.
Copy this path minus the "pkg_config"
Add :pathCopied in the value og the PATH variable
In the terminal type
	`find /usr/local -name opencv.pc`
and copy the path minus the opencv.pc part
In the Qt creator, add a new variable **PKG_CONFIG_PATH** and past in value the path previously copied

Finally we create the .pro file:

                #-------------------------------------------------
                #
                # Project created by QtCreator 2018-01-26T21:49:39
                #
                #-------------------------------------------------
                QT       += core gui
                greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
                TARGET = MyApp
                TEMPLATE = app
                QT_CONFIG -= no-pkg-config
                CONFIG  += link_pkgconfig
                PKGCONFIG += opencv
                # The following define makes your compiler emit warnings if you use
                # any feature of Qt which has been marked as deprecated (the exact warnings
                # depend on your compiler). Please consult the documentation of the
                # deprecated API in order to know how to port your code away from it.
                DEFINES += QT_DEPRECATED_WARNINGS
                # You can also make your code fail to compile if you use deprecated APIs.
                # In order to do so, uncomment the following line.
                # You can also select to disable deprecated APIs only up to a certain version of Qt.
                #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
                SOURCES += \
                        main.cpp \
                        mainwindow.cpp \
                        someSourceCode.cpp
                LIBS += -L/usr/local/lib/
                HEADERS += \
                        mainwindow.h\
                        someSourceCode.h
                FORMS += \
                        mainwindow.ui
                RESOURCES += resources.qrc

Your OpenCV/Qt application should compile and run without problems.