package/opencv: add a choice for selecting the gui toolkit

In OpenCV, only one GUI toolkit may be used at any one time, so group
the two existing options into a choice to make this situation explicit.

This will also be useful when we later add support for Qt5 and gtk3.

Suggested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
[yann.morin.1998@free.fr: tweak commit log]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/opencv/Config.in

@@ -52,6 +52,50 @@ config BR2_PACKAGE_OPENCV_LIB_HIGHGUI
 	  Include opencv_highgui (high-level gui and media i/o) module into the
 	  OpenCV build.
 
+choice
+	prompt "gui toolkit"
+	depends on BR2_PACKAGE_OPENCV_LIB_HIGHGUI
+	help
+	  GUI toolkit to be used by the opencv_highgui module.
+
+config BR2_PACKAGE_OPENCV_GUI_NONE
+	bool "none"
+
+config BR2_PACKAGE_OPENCV_WITH_GTK
+	bool "gtk2"
+	depends on BR2_ARCH_HAS_ATOMICS # libgtk2 -> cairo
+	depends on BR2_USE_MMU # libgtk2 -> libglib2
+	depends on BR2_USE_WCHAR # libgtk2 -> libglib2
+	depends on BR2_TOOLCHAIN_HAS_THREADS # libgtk2 -> libglib2
+	depends on BR2_INSTALL_LIBSTDCPP
+	depends on BR2_PACKAGE_XORG7
+	select BR2_PACKAGE_LIBGTK2
+
+comment "gtk2 needs X.org and a toolchain w/ wchar, threads, C++"
+	depends on BR2_USE_MMU # libgtk2 -> glib2
+	depends on BR2_ARCH_HAS_ATOMICS # libgtk2 -> cairo
+	depends on !BR2_PACKAGE_XORG7 || \
+		!BR2_USE_WCHAR || \
+		!BR2_TOOLCHAIN_HAS_THREADS || \
+		!BR2_INSTALL_LIBSTDCPP
+
+config BR2_PACKAGE_OPENCV_WITH_QT
+	bool "qt4"
+	depends on BR2_INSTALL_LIBSTDCPP
+	depends on BR2_USE_MMU # qt
+	select BR2_PACKAGE_QT
+	select BR2_PACKAGE_QT_STL
+	select BR2_PACKAGE_QT_GUI_MODULE
+	select BR2_PACKAGE_QT_TEST
+	help
+	  Use Qt with QtTest module and STL support
+
+comment "qt4 needs a toolchain w/ C++"
+	depends on BR2_USE_MMU # qt
+	depends on !BR2_INSTALL_LIBSTDCPP
+
+endchoice
+
 config BR2_PACKAGE_OPENCV_LIB_IMGCODECS
 	bool "imgcodecs"
 	select BR2_PACKAGE_OPENCV_LIB_IMGPROC
@@ -209,17 +253,6 @@ comment "gstreamer-1.x support needs a toolchain w/ wchar, threads"
 
 endchoice
 
-config BR2_PACKAGE_OPENCV_WITH_GTK
-	bool "gtk support"
-	depends on BR2_PACKAGE_XORG7
-	depends on BR2_USE_WCHAR # libgtk2 -> libglib2
-	depends on BR2_TOOLCHAIN_HAS_THREADS # libgtk2 -> libglib2
-	depends on BR2_INSTALL_LIBSTDCPP
-	depends on BR2_USE_MMU # libgtk2 -> glib2
-	depends on BR2_ARCH_HAS_ATOMICS # libgtk2 -> cairo
-	depends on BR2_PACKAGE_OPENCV_LIB_HIGHGUI
-	select BR2_PACKAGE_LIBGTK2
-
 config BR2_PACKAGE_OPENCV_WITH_JASPER
 	bool "jpeg2000 support"
 	select BR2_PACKAGE_JASPER
@@ -242,18 +275,6 @@ config BR2_PACKAGE_OPENCV_WITH_PNG
 	help
 	  Use shared libpng from the target system.
 
-config BR2_PACKAGE_OPENCV_WITH_QT
-	bool "qt backend support"
-	depends on BR2_INSTALL_LIBSTDCPP
-	depends on BR2_USE_MMU # qt
-	depends on BR2_PACKAGE_OPENCV_LIB_HIGHGUI
-	select BR2_PACKAGE_QT
-	select BR2_PACKAGE_QT_STL
-	select BR2_PACKAGE_QT_GUI_MODULE
-	select BR2_PACKAGE_QT_TEST
-	help
-	  Use Qt with QtTest module and STL support
-
 config BR2_PACKAGE_OPENCV_WITH_TIFF
 	bool "tiff support"
 	select BR2_PACKAGE_TIFF