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

[Laurent Pinchart]

Hi Tomi,

On Fri, May 27, 2022 at 09:08:37AM +0300, Tomi Valkeinen wrote:
> On 26/05/2022 18:55, Laurent Pinchart wrote:
> > 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.
> 
> Sounds good to me.
> 
> >> +
> >> +    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.
> 
> Let's discuss these in the thread for the following patch.
> 
> >> +
> >> +        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.
> 
> Hmm... How do we invalidate the caches if we keep the buffers mapped?

QBUF/DQBUF are supposed to handle that.

-- 
Regards,

Laurent Pinchart