Opencv 4.1: different pkg-config library name

[pliablepixels]

OpenCV 4.1 (not sure of earlier versions) seems to use opencv4 instead of opencv for pkg-config (assuming you used -D OPENCV_GENERATE_PKGCONFIG=ON)

Thanks for your fork. It works wonderfully with OpenCV 4.1 and CUDA 10.1

[AlexeyAB]

@pliablepixels Hi, thanks!

Do you think we should use both opencv and opencv4 for supporting both OpenCV 4.x and OpenCV3.x/2.x?

I.e. use

LDFLAGS+= `pkg-config --libs opencv`
COMMON+= `pkg-config --cflags opencv`
LDFLAGS+= `pkg-config --libs opencv4`
COMMON+= `pkg-config --cflags opencv4`

instead of:

darknet/Makefile

Lines 79 to 80 in 5ec3592

	LDFLAGS+= `pkg-config --libs opencv`
	COMMON+= `pkg-config --cflags opencv`

[AlexeyAB]

@cenit Hi, what do you think about this?

[pliablepixels]

I agree, I actually did something like

 OPENCVPKG=`pkg-config --libs opencv || pkg-config --libs opencv4`

I did not PR, because I did not investigate if pkg-config allows alias names etc. which is cleaner if it exists.

[cenit]

The problem here is only for the makefile. Unfortunately I think it’s not as easy as you say, because if you have both installed then you risk a mess. Autotools usually come to the rescue here, but I’d say it is an overkill.
First of all, i’d revert your common and ldflag order, so to have opencv4 appear first on the build line wrt opencv. Second, includes and linked files might even be ok since the first should resolve everything, but what about defines? You’d have defines for both version active on the same command line. You should test it thoroughly in a specific corner case maybe before pushing it. I think having both is becoming a little bit too common

[SalahAdDin]

pjreddie#1348 This is a try to add supporting OpenCV 4.

[cenit]

close thanks to #4896 fixing makefile also for OpenCV 4.1