[libcamera-devel] How to displace viewfinder using DRM/KMS

[Laurent Pinchart]

Hi Eric,

On Wed, Oct 20, 2021 at 05:05:56PM +0100, Eric Curtin wrote:
> Hi Guys,
> 
> To start thanks so much for your work on libcamera.
> 
> I am interested in running the cam app via DRM/KMS on my laptop and
> afterwards on my raspberry pi. I have figured out how to select the
> correct camera and select the correct display to output to. But how
> can I get them to play nicely together without "No mode matching
> 1280x720", "Failed to configure frame sink", "Failed to start camera
> session", "Unable to find display pipeline for format MJPEG", etc.
> 
> I'm a bit of a newbie to graphics and cameras, so any help to get this
> running would be greatly appreciated!
> 
> $ sudo LD_LIBRARY_PATH="/usr/local/lib:/usr/local/lib64" cam -c 1 -C4 -DeDP-1
> [7:12:21.427200555] [75751]  INFO Camera camera_manager.cpp:293 libcamera v0.0.0+3119-2f75a7e5
> Using camera \_SB_.PCI0.XHC_.RHUB.HS08-8:1.0-13d3:5405 as cam0
> [7:12:21.534685678] [75751]  INFO Camera camera.cpp:937 configuring streams: (0) 1280x720-MJPEG
> No mode matching 1280x720

The DRM/KMS support in the cam application can't handle the KMS scaling
API at this point, so it requires configuring the camera to output a
resolution that matches the mode exactly. You can check the resolutions
supported by the KMS connector (using xrandr if you're running X for
instance), and then use the -s argument to cam to select the stream
resolution, assuming the camera is able to produce a matchin resolution.

It would be nice to lift this limitation, it will require a bit of work
in the cam application.

> Failed to configure frame sink
> Failed to start camera session
> curtine at curt 17:00:12 1
> $ sudo LD_LIBRARY_PATH="/usr/local/lib:/usr/local/lib64" cam -c 1 -C4 -DDP-1
> [7:12:25.392692897] [75760]  INFO Camera camera_manager.cpp:293
> libcamera v0.0.0+3119-2f75a7e5
> Using camera \_SB_.PCI0.XHC_.RHUB.HS08-8:1.0-13d3:5405 as cam0
> [7:12:25.497724802] [75760]  INFO Camera camera.cpp:937 configuring
> streams: (0) 1280x720-MJPEG
> Unable to find display pipeline for format MJPEG

That's the next issue, you also need a format that your display device
can handle natively. MJPEG won't be one of them. I assume you're using a
USB camera, so you could try passing `-s pixelformat=YUYV` to cam. With
a bit of luck, your display controller will support that format.
Otherwise, you won't be able to use cam and the KMS sink with that
camera and display controller.

> Failed to configure frame sink
> Failed to start camera session

-- 
Regards,

Laurent Pinchart