RGBDSensorWrapper example fails to run becasue fakeDepthCamera needs to implement yarp::dev::FrameGrabberControls

[traversaro]

Describe the bug
The command described in https://github.com/robotology/yarp/blame/b7983c941952a3aafa7de7dd4aeeb574c1865799/example/dev/RGBD/README.md#L21 :

yarpdev --device RGBDSensorWrapper --name /server --subdevice fakeDepthCamera --mode ball 

is failing with the following error:

straversaro@iiticublap103:~/src/idjl-superbuild/build3/idjl/YARP$ yarpdev --device RGBDSensorWrapper --name /server --subdevice fakeDepthCamera --mode ball 
[INFO]RGBDSensorWrapper: using default 'period' parameter of  0.03 s 
[INFO]RGBDSensorWrapper: ROS configuration parameters are not set, skipping ROS topic initialization. 
yarp: Port /server/rpc:i active at tcp://192.168.1.10:10007/
yarp: Port /server/rgbImage:o active at tcp://192.168.1.10:10008/
yarp: Port /server/depthImage:o active at tcp://192.168.1.10:10009/
[DEBUG]opening IRGBDSensor subdevice
[INFO]Test grabber period 0.0333333 / freq 30 , mode [ball]
[INFO]created device <test_grabber>. See C++ class yarp::dev::TestFrameGrabber for documentation.
[INFO]created device <fakeDepthCamera>. See C++ class yarp::dev::fakeDepthCameraDriver for documentation.
[ERROR]RGBD wrapper: error configuring interfaces for parsers 
[ERROR]RGBDSensorWrapper: error while opening subdevice
yarpdev: ***ERROR*** driver <RGBDSensorWrapper> was found but could not open
[ERROR]yarpdev: ***ERROR*** device not available.
[INFO]Suggestions:
[INFO]+ Do "yarpdev --list" to see list of supported devices.
[INFO]+ Or append "--verbose" option to get more information.

Expected behavior
The one described in the tutorial.

Configuration (please complete the following information):

• OS: Ubuntu 18.04
• yarp version: current devel
• compiler: Gcc 7.3

[PeterBowman]

fakeDepthCamera needs to implement yarp::dev::FrameGrabberControls. yarp::dev::RGBDSensorWrapper expects this interface in its subdevices since YARP 2.3.72.1.

[traversaro]

Thanks @PeterBowman .

[Nicogene]

fakeDepthCamera needs to implement yarp::dev::FrameGrabberControls.

@aerydna and me noticed this bug yesterday and it can be easily fixed simply adding the interface and the respective methods with {return false} implementation or making this interface optional for the open of the device.