python - python中的用户指针

Question

*我正在尝试显示使用 v4l 捕获的网络摄像头的预览。

下面是代码的概念:

from ctypes import *
from v4l2 import *
from Image import fromstring
from Tkinter import Tk, Label
from ImageTk import PhotoImage
from ctypes.util import find_library

libc = CDLL(find_library('c'))
posix_memalign = libc.posix_memalign
getpagesize = libc.getpagesize


device_name = '/dev/video0'
ps = preview_settings = {
    'width': 320,
    'height': 240,
    'pixformat': 'RGB',
    }
PIX_FMT = V4L2_PIX_FMT_RGB555


preview = Tk()
image = PhotoImage(ps['pixformat'], (ps['width'], ps['height']))
label = Label(preview, text='Preview', image=image, width=ps['width'], height=ps['height'])
label.pack()


capability = v4l2_capability()
size = v4l2_frmsizeenum()
format = v4l2_format()
request = v4l2_requestbuffers()
buffer = v4l2_buffer()
b_address = c_void_p()
frame_name_count = '0'
type = V4L2_BUF_TYPE_VIDEO_CAPTURE

device = open(device_name, 'rw')

ioctl(device, VIDIOC_QUERYCAP, addr(capability))

size.pixel_format = PIX_FMT 
size.index = 0

format.type = type
format.fmt.pix.pixelformat = PIX_FMT
format.fmt.pix.width = size.discrete.width
format.fmt.pix.height = size.discrete.height
format.fmt.pix.field = V4L2_FIELD_NONE
format.fmt.pix.bytesperline = 0
format.fmt.pix.sizeimage = 0

request.type = type
request.memory = V4L2_MEMORY_USERPTR
request.count = 1

ioctl(device, VIDIOC_S_FMT, addr(format))

ioctl(device, VIDIOC_G_FMT, addr(format))

ioctl(device, VIDIOC_REQBUFS, addr(request))

posix_memalign(addressof(b_address), getpagesize(), format.fmt.pix.sizeimage)

buffer.type = request.type
buffer.memory = request.memory
buffer.index = 0
buffer.m.userptr = b_address.value
buffer.length = format.fmt.pix.sizeimage

while True:

    ioctl(device, VIDIOC_QBUF, addr(buffer))

    ioctl(device, VIDIOC_STREAMON, cast(type, c_void_p))

    ioctl(device, VIDIOC_DQBUF, addr(buffer))

    preview_data = string_at(buffer.m.userptr, buffer.length)
    im = fromstring(ps['pixformat'], (ps['width'], ps['height']), preview_data)
    image.paste(im)
    preview.update()

我得到 ValueError: 没有足够的图像数据

---

好吧，我导入

c_lib = CDLL(find_library('c'))
posix_memalign = c_lib.posix_memalign
getpagesize = c_lib.getpagesize

然后是

ioctl(device, VIDIOC_S_FMT, addr(format))
ioctl(device, VIDIOC_G_FMT, addr(format))

诸如此类，我尝试获取内存

posix_memalign(addressof(b_address), getpagesize(), format.fmt.pix.sizeimage)

现在 b_address 不再 = Noneb_address 类似于 c_void_p(145014784)

然后我开始循环、QBUF、DQBUF 等。

问题是，当我调用 pygame.image.frombuffer 时

pg_img = pygame.image.frombuffer(
         buffer.m.userptr,
         (format.fmt.pix.width, format.fmt.pix.height),
         preview_settings['pixformat']
         )

我得到 TypeError: expected a character buffer object

Answer 1

看起来像ctypes.string_at(address, size)是你想要的。这将为您提供一个 python 字符串缓冲区，其中包含指针地址处的内存内容。这应该适合传递给 Image.fromstring 或 pygame.image.frombuffer。