[libcamera-devel] [PATCH v2 10/19] py: examples: Add simple-capture.py

[Laurent Pinchart]

Hi Tomi,

Thank you for the patch.

On Tue, May 24, 2022 at 02:46:01PM +0300, Tomi Valkeinen wrote:
> Add an example to showcase the more-or-less minimal capture case.

Niiiice :-) This is a really good start. I'd like more comments, but
that can be done on top.

> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> ---
>  src/py/examples/simple-capture.py | 153 ++++++++++++++++++++++++++++++
>  1 file changed, 153 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..45df9e7a
> --- /dev/null
> +++ b/src/py/examples/simple-capture.py
> @@ -0,0 +1,153 @@
> +#!/usr/bin/env python3
> +
> +# SPDX-License-Identifier: BSD-3-Clause
> +# Copyright (C) 2022, Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> +
> +# A simple minimal capture example showing:
> +# - How to setup the camera
> +# - Capture frames in a blocking manner
> +# - Memory map the frames
> +# - How to stop the camera
> +
> +import argparse
> +import binascii
> +import libcamera as libcam
> +import libcamera.utils
> +import sys
> +
> +
> +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
> +
> +    camconfig = cam.generate_configuration([libcam.StreamRole.StillCapture])

I'm going to bikeshed a bit as this will be used as a starting point by
many people, sorry.

As the Python coding style uses snake_case, should this be cam_config ?
The next variable would be stream_config.

I'd also use the ViewFinder role to match the C++ simple-cam.

> +
> +    streamconfig = camconfig.at(0)
> +
> +    if args.format:
> +        fmt = libcam.PixelFormat(args.format)
> +        streamconfig.pixel_format = fmt
> +
> +    if args.size:
> +        w, h = [int(v) for v in args.size.split('x')]
> +        streamconfig.size = libcam.Size(w, h)
> +
> +    ret = cam.configure(camconfig)
> +    assert ret == 0
> +
> +    stream = streamconfig.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'Capturing {num_bufs} frames with {streamconfig}')

This can be done on top, but I'd like to capture more frames (100 for
instance), to show how to requeue requests.

> +
> +    # 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
> +
> +    # Queue the requests to the camera
> +
> +    for req in reqs:
> +        ret = cam.queue_request(req)
> +        assert ret == 0
> +
> +    # Wait until the requests are finished
> +
> +    reqs = []
> +
> +    while True:
> +        # cm.read_event() blocks until there is an event
> +        cm.read_event()
> +
> +        # Get all the ready requests
> +        ready_reqs = cm.get_ready_requests()

Integrating a simple event loop (maybe based on the Python asyncio
module ?) would be good here.

> +
> +        reqs += ready_reqs
> +
> +        if len(reqs) >= num_bufs:
> +            break
> +
> +    # Process the captured frames
> +
> +    for i, req in enumerate(reqs):
> +        assert i == req.cookie
> +
> +        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()))
> +
> +        # Use MappedFrameBuffer to access the pixel data with CPU. We calculate
> +        # the crc for each plane.
> +
> +        with libcamera.utils.MappedFrameBuffer(fb) as mfb:
> +            crcs = [binascii.crc32(p) for p in mfb.planes]

Mapping buffers is expensive, this should be done before starting the
camera.

> +
> +        meta = fb.metadata
> +
> +        print('seq {}, bytes {}, CRCs {}'
> +              .format(meta.sequence, meta.bytesused, crcs))
> +
> +    # 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())

-- 
Regards,

Laurent Pinchart