[libcamera-devel] [PATCH v3 27/30] py: examples: Add simple-capture.py

[Tomi Valkeinen]

On 30/05/2022 12:57, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Fri, May 27, 2022 at 05:44:44PM +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 | 159 ++++++++++++++++++++++++++++++
>>   1 file changed, 159 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..4b0c3f0c
>> --- /dev/null
>> +++ b/src/py/examples/simple-capture.py
>> @@ -0,0 +1,159 @@
>> +#!/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
>> +#
>> +# 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 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
>> +
>> +    cam_config = cam.generate_configuration([libcam.StreamRole.Viewfinder])
>> +
>> +    stream_config = cam_config.at(0)
>> +
>> +    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
>> +
>> +    num_bufs = len(allocator.buffers(stream))
>> +
>> +    print(f'Capturing {num_bufs} frames 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(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()
> 
> This is the only example I'm not sure about, as I'd like to avoid
> encouraging people to not use an event loop. I'm tempted to drop this
> one and rename simple-continuous-capture.py to simple-capture.py.

I can change this from a loop blocking in cm.read_event() to a loop 
blocking in select, as it's just a few lines more. But I don't think it 
materially changes the example.

I really like the simple-capture.py, as it's an example in a single 
function, so you just read it from top to bottom and it makes sense. In 
simple-continuous-capture.py you need to jump back and forth the 
functions a bit.

Although I could also add a few more lines of code to add reuse & 
requeuing of the requests and interrupt via keypress, and still keep it 
in a single function.

  Tomi