Yocto: cmake is missing header - how to DEPEND dev-package? - opencv

Question

I am including opencv with custom build parameters in my Yocto image. For that I have an opencv_4.1.0.bbappend recipe, in which I set custom options, specifically FFMPEG. The recipe goes something like this:
DEPENDS += "ffmpeg libpng"
EXTRA_OECMAKE_append += "-DWITH_FFMPEG=ON -DWITH_GTK=OFF" # and some other options
During configure I get cmake errors and can't seem to figure out, how to satisfy the header dependencies. The errors go like this (I assume this is the reason for do_configure to fail):
CheckIncludeFile.c:1:10: fatal error: /home/janos/dev/yocto/build/tmp/work/core2-64-poky-linux/opencv/4.1.0-r0/recipe-sysroot/usr/include/libpng/png.h: No such file or directory
1 | #include </home/janos/dev/yocto/build/tmp/work/core2-64-poky-linux/opencv/4.1.0-r0/recipe-sysroot/usr/include/libpng/png.h>
CheckIncludeFile.c:1:10: fatal error: sys/videoio.h: No such file or directory
1 | #include <sys/videoio.h>
Focusing on the missing png.h header first, I am tempted to depend libpng-dev, as I also would apt install it. But there is no package for it.
When I search oe-pkgdata-util list-pkg-files -p libpng, I can find the header in a libpng-dev package:
...
libpng-dev:
/usr/bin/libpng-config
/usr/bin/libpng16-config
/usr/include/libpng16/png.h
/usr/include/libpng16/pngconf.h
/usr/include/libpng16/pnglibconf.h
/usr/include/png.h
...
...
I can also find it in libpng-src and also ffmpeg-src package (oe-pkgdata-util find-path "*png.h" was my friend). But all of these -dev and -src packages I cannot depend on in DEPENDS.
How can I get my recipe to know those headers?
Target machine is raspberrypi4-64, on which the recipe is configuring and compiling well - it fails when I build for qemux86-64, which I use for testing. Namely, my test command is MACHINE="qemux86-64" bitbake opencv.

Answer 1

It doesn't really answer the question which I though was the question - but this is how the opencv recipe is easily configured:
PACKAGECONFIG = "python3 libav libv4l v4l"
Looking into the opencv 4.1.0 recipe (opencv_4.1.0.bb), I could see that FFMPEG gets enabled with the libav configurable option.
As a result of depending FFMEPG, I had to whitelist "commercial" licenses in my local.conf file:
LICENSE_FLAGS_WHITELIST = "commercial"
Looking into ./build/tmp/work/aarch64-poky-linux/opencv/4.1.0-r0/temp/log.do_configure shows that opencv is correctly configured without GUI, with v4l/v4l2:, FFMPEG, python3, etc.
And so python3 in the resulting image:
import cv2
print(cv2.getBuildInformation())