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

[Tomi Valkeinen]

On 05/06/2022 15:24, Jacopo Mondi wrote:
> 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

Thanks, you're right.

>> +
>> +    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..

I guess one could argue if the whole print is of any use =). But here I 
thought it'll show how at the end the queued number stops increasing 
while we still get new frames.

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

Thanks!