[libcamera-devel] [PATCH v4 13/16] py: examples: Add simple-capture.py

[Jacopo Mondi]

Hi Tomi,

On Mon, May 30, 2022 at 05:27:19PM +0300, Tomi Valkeinen wrote:
> Add an example to showcase the more-or-less minimal capture case.
>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> ---
>  src/py/examples/simple-capture.py | 162 ++++++++++++++++++++++++++++++
>  1 file changed, 162 insertions(+)
>  create mode 100755 src/py/examples/simple-capture.py
>
> diff --git a/src/py/examples/simple-capture.py b/src/py/examples/simple-capture.py
> new file mode 100755
> index 00000000..ff8cef4f
> --- /dev/null
> +++ b/src/py/examples/simple-capture.py
> @@ -0,0 +1,162 @@
> +#!/usr/bin/env python3
> +
> +# SPDX-License-Identifier: BSD-3-Clause
> +# Copyright (C) 2022, Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> +
> +# A simple capture example showing:
> +# - How to setup the camera
> +# - Capture certain number of frames in a blocking manner
> +# - How to stop the camera
> +#
> +# This simple example is, in many ways, too simple. The purpose of the example
> +# is to introduce the concepts. A more realistic example is given in
> +# simple-continuous-capture.py.
> +
> +import argparse
> +import libcamera as libcam
> +import sys
> +
> +# Number of frames to capture
> +TOTAL_FRAMES = 30
> +
> +
> +def main():
> +    parser = argparse.ArgumentParser()
> +    parser.add_argument('-c', '--camera', type=str, default='1',
> +                        help='Camera index number (starting from 1) or part of the name')
> +    parser.add_argument('-f', '--format', type=str, help='Pixel format')
> +    parser.add_argument('-s', '--size', type=str, help='Size ("WxH")')
> +    args = parser.parse_args()
> +
> +    cm = libcam.CameraManager.singleton()
> +
> +    try:
> +        if args.camera.isnumeric():
> +            cam_idx = int(args.camera)
> +            cam = next((cam for i, cam in enumerate(cm.cameras) if i + 1 == cam_idx))
> +        else:
> +            cam = next((cam for cam in cm.cameras if args.camera in cam.id))
> +    except Exception:
> +        print(f'Failed to find camera "{args.camera}"')
> +        return -1
> +
> +    # 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)
> +
> +    print(f'Capturing {TOTAL_FRAMES} frames with {stream_config}')

Could you move this after setting the sizes and formats ? Or maybe
even after the camera has been configured..

Otherwise it will print the default configuration

> +
> +    if args.format:
> +        fmt = libcam.PixelFormat(args.format)
> +        stream_config.pixel_format = fmt
> +
> +    if args.size:
> +        w, h = [int(v) for v in args.size.split('x')]
> +        stream_config.size = libcam.Size(w, h)
> +
> +    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

We have a rather bad API when it comes to control how many buffer to
allocate. Python can only reflect that, so I guess it's fine to just
check for > 0 here

> +
> +    num_bufs = len(allocator.buffers(stream))
> +
> +    # 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(i)
> +
> +        buffer = allocator.buffers(stream)[i]
> +        ret = req.add_buffer(stream, buffer)
> +        assert ret == 0
> +
> +        reqs.append(req)
> +
> +    # Start the camera
> +
> +    ret = cam.start()
> +    assert ret == 0
> +
> +    # frames_queued and frames_done track the number of frames queued and done
> +
> +    frames_queued = 0
> +    frames_done = 0
> +
> +    # Queue the requests to the camera
> +
> +    for req in reqs:
> +        ret = cam.queue_request(req)
> +        assert ret == 0
> +        frames_queued += 1
> +
> +    # The main loop. Wait for the queued Requests to complete, process them,
> +    # and re-queue them again.
> +
> +    while frames_done < TOTAL_FRAMES:
> +        # cm.get_ready_requests() blocks until there is an event and returns
> +        # all the ready requests. Here we should almost always get a single
> +        # Request, but in some cases there could be multiple or none.
> +
> +        reqs = cm.get_ready_requests()
> +
> +        for req in reqs:
> +            frames_done += 1
> +
> +            buffers = req.buffers
> +
> +            # 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.
> +
> +            assert len(buffers) == 1
> +
> +            stream, fb = next(iter(buffers.items()))
> +
> +            # Here we could process the received buffer. In this example we only
> +            # print a few details below.
> +
> +            meta = fb.metadata
> +
> +            print("seq {:3}, bytes {}, frames queued/done {:3}/{:<3}"
> +                  .format(meta.sequence,
> +                          '/'.join([str(p.bytes_used) for p in meta.planes]),
> +                          frames_queued, frames_done))

I wonder if printing the number of queued requests is of any use..

All minors, the rest looks good to me
Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>

Thanks
   j

> +
> +            # If we want to capture more frames we need to queue more Requests.
> +            # We could create a totally new Request, but it is more efficient
> +            # to reuse the existing one that we just received.
> +            if frames_queued < TOTAL_FRAMES:
> +                req.reuse()
> +                cam.queue_request(req)
> +                frames_queued += 1
> +
> +    # Stop the camera
> +
> +    ret = cam.stop()
> +    assert ret == 0
> +
> +    # Release the camera
> +
> +    ret = cam.release()
> +    assert ret == 0
> +
> +    return 0
> +
> +
> +if __name__ == '__main__':
> +    sys.exit(main())
> --
> 2.34.1
>