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

[Tomi Valkeinen]

On 30/05/2022 13:36, Tomi Valkeinen wrote:
> 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.

Actually, I don't know if that makes sense. If you want to write a short 
script that captures, say, 50 frames from a camera, why would you 
implement an event loop instead of just a blocking loop until you got 
your frames? I don't see anything wrong with that.

  Tomi