Finally, found the reason of the black/white screen: when installing through unreal engine, unreal engine copies required files to sdcard folder including ARToolkit folder. When the app is installed this way it can locate camera_para.dat file and works fine.
And if the app is installed other way after UE copied the files to the folder it also works.
However when the app was never launched on a device through unreal engine it includes the folder to APK, but the app can’t locate it because it’s trying to locate it in a wrong folder.
I have checked your code and it seems the path to the file is generated in ARToolkitDevice.cpp:
111: FString AbsoluteContentPath = GFilePathBase + TEXT("/UE4Game/") + FApp::GetGameName() + TEXT("/") + FString::Printf(TEXT("%s/Content/"), FApp::GetGameName());
05-01 04:26:41.899 12831 12845 E libar : Error (2): unable to open camera parameters file “/storage/emulated/0/UE4Game/ARCHON/ARCHON/Content/ARToolkit/Data/camera_para.dat” for reading.
Guess what? /storage/emulated folder is empty.
‘/storage/emulated/0/’ - this part of the path is taken from GFilePathBase extern variable. But i can’t find the code which sets it.
Is this ARToolkitDevice class is made by you or artoolkit community?
Do you know where the variable is set?
Any help would be very much appreciated.