[libcamera-devel] [PATCH v4 14/16] py: examples: Add simple-continuous-capture.py

[Jacopo Mondi]

Hi Tomi,

On Mon, May 30, 2022 at 05:27:20PM +0300, Tomi Valkeinen wrote:
> Add a slightly more complex, and I think a more realistic, example,
> where the script reacts to events and re-queues the buffers.
>

My first question is if such similar examples are useful or they will
become a maintainership burden.

>From my side, the more examples the better, but I think the question
if it's woth it stays..

> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> ---
>  src/py/examples/simple-continuous-capture.py | 189 +++++++++++++++++++
>  1 file changed, 189 insertions(+)
>  create mode 100755 src/py/examples/simple-continuous-capture.py
>
> diff --git a/src/py/examples/simple-continuous-capture.py b/src/py/examples/simple-continuous-capture.py
> new file mode 100755
> index 00000000..d0f8a7e9
> --- /dev/null
> +++ b/src/py/examples/simple-continuous-capture.py
> @@ -0,0 +1,189 @@
> +#!/usr/bin/env python3
> +
> +# SPDX-License-Identifier: BSD-3-Clause
> +# Copyright (C) 2022, Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> +
> +# A simple capture example extending the simple-capture.py example:
> +# - Capture frames using events from multiple cameras
> +# - Listening events from stdin to exit the application
> +# - Memory mapping the frames and calculating CRC
> +
> +import binascii
> +import libcamera as libcam
> +import libcamera.utils
> +import selectors
> +import sys
> +
> +
> +# A container class for our state per camera
> +class CameraCaptureContext:
> +    idx: int
> +    cam: libcam.Camera
> +    reqs: list[libcam.Request]
> +    mfbs: dict[libcam.FrameBuffer, libcamera.utils.MappedFrameBuffer]
> +
> +    def __init__(self, cam, idx):
> +        # Acquire the camera for our use
> +
> +        ret = cam.acquire()
> +        assert ret == 0
> +
> +        # Configure the camera
> +
> +        cam_config = cam.generate_configuration([libcam.StreamRole.Viewfinder])
> +
> +        stream_config = cam_config.at(0)
> +
> +        ret = cam.configure(cam_config)
> +        assert ret == 0
> +
> +        stream = stream_config.stream
> +
> +        # Allocate the buffers for capture
> +
> +        allocator = libcam.FrameBufferAllocator(cam)
> +        ret = allocator.allocate(stream)
> +        assert ret > 0
> +
> +        num_bufs = len(allocator.buffers(stream))
> +
> +        print(f'cam{idx} ({cam.id}): capturing {num_bufs} buffers with {stream_config}')
> +
> +        # Create the requests and assign a buffer for each request
> +
> +        reqs = []
> +        for i in range(num_bufs):
> +            # Use the buffer index as the "cookie"
> +            req = cam.create_request(idx)
> +
> +            buffer = allocator.buffers(stream)[i]
> +            ret = req.add_buffer(stream, buffer)
> +            assert ret == 0
> +
> +            reqs.append(req)
> +
> +        self.idx = idx
> +        self.cam = cam
> +        self.reqs = reqs
> +        self.mfbs = dict([(fb, libcamera.utils.MappedFrameBuffer(fb).mmap()) for fb in allocator.buffers(stream)])

Not that relevant, but you could populate self.reqs directly and
append a {buffer,  libcamera.utils.MappedFrameBuffer(fb).mmap()} pair
to the self.mfbs dictionary in the request creation loop ?

> +
> +    def uninit_camera(self):
> +        # Stop the camera
> +
> +        ret = self.cam.stop()
> +        assert ret == 0
> +
> +        # Release the camera
> +
> +        ret = self.cam.release()
> +        assert ret == 0
> +
> +
> +# A container class for our state
> +class CaptureContext:
> +    cm: libcam.CameraManager
> +    camera_contexts: list[CameraCaptureContext] = []
> +
> +    def handle_camera_event(self):
> +        # cm.get_ready_requests() will not block here, as we know there is an event
> +        # to read.
> +
> +        reqs = self.cm.get_ready_requests()
> +
> +        # Process the captured frames
> +
> +        for req in reqs:
> +            self.handle_request(req)
> +
> +        return True
> +
> +    def handle_request(self, req: libcam.Request):
> +        cam_ctx = self.camera_contexts[req.cookie]
> +
> +        buffers = req.buffers
> +
> +        assert len(buffers) == 1
> +
> +        # A ready Request could contain multiple buffers if multiple streams
> +        # were being used. Here we know we only have a single stream,
> +        # and we use next(iter()) to get the first and only buffer.
> +
> +        stream, fb = next(iter(buffers.items()))
> +
> +        # Use the MappedFrameBuffer to access the pixel data with CPU. We calculate
> +        # the crc for each plane.
> +
> +        mfb = cam_ctx.mfbs[fb]
> +        crcs = [binascii.crc32(p) for p in mfb.planes]
> +
> +        meta = fb.metadata
> +
> +        print('cam{:<6} seq {:<6} bytes {:10} CRCs {}'
> +              .format(cam_ctx.idx,
> +                      meta.sequence,
> +                      '/'.join([str(p.bytes_used) for p in meta.planes]),
> +                      crcs))
> +
> +        # We want to re-queue the buffer we just handled. Instead of creating
> +        # a new Request, we re-use the old one. We need to call req.reuse()
> +        # to re-initialize the Request before queuing.
> +
> +        req.reuse()
> +        cam_ctx.cam.queue_request(req)
> +
> +    def capture(self):
> +        # Queue the requests to the camera
> +
> +        for cam_ctx in self.camera_contexts:
> +            for req in cam_ctx.reqs:
> +                ret = cam_ctx.cam.queue_request(req)
> +                assert ret == 0
> +
> +        # Use Selector to wait for events from the camera and from the keyboard
> +
> +        sel = selectors.DefaultSelector()
> +        sel.register(sys.stdin, selectors.EVENT_READ, handle_key_event)
> +        sel.register(self.cm.event_fd, selectors.EVENT_READ, lambda: self.handle_camera_event())
> +
> +        running = True
> +
> +        while running:
> +            events = sel.select()
> +            for key, mask in events:
> +                # If the handler return False, we should exit
> +                if not key.data():
> +                    running = False
> +
> +
> +def handle_key_event():
> +    sys.stdin.readline()
> +    print('Exiting...')
> +    return False

Nit: why is this a global function handle_camera_event() a class
member ?

To be honest I would get rid of the CaptureContext class and open-code
CaptureContext::capture() in your main function, with all the handlers
being global functions. Not a big deal though

> +
> +
> +def main():
> +    cm = libcam.CameraManager.singleton()
> +
> +    ctx = CaptureContext()
> +    ctx.cm = cm
> +
> +    for idx, cam in enumerate(cm.cameras):
> +        cam_ctx = CameraCaptureContext(cam, idx)

Can't you start the camera here ?

> +        ctx.camera_contexts.append(cam_ctx)
> +
> +    # Start the cameras
> +
> +    for cam_ctx in ctx.camera_contexts:
> +        ret = cam_ctx.cam.start()
> +        assert ret == 0
> +
> +    ctx.capture()
> +
> +    for cam_ctx in ctx.camera_contexts:
> +        cam_ctx.uninit_camera()
> +
> +    return 0
> +
> +
> +if __name__ == '__main__':
> +    sys.exit(main())

Nits apart
Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>

Thanks
   j

> --
> 2.34.1
>