python中的用户指针 [英] user pointer in python

问题描述

*我正在尝试显示使用v4l捕获的网络摄像头的预览.

*I am trying to display preview from webcam captured using v4l.

以下是代码的外观:

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:图像数据不足

好吧，我导入

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

然后在

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

之类的东西，我尝试获取内存

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

现在b_address不再= None b_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

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

我得到 TypeError:预期为字符缓冲区对象

推荐答案

类似 ctypes.string_at(地址，大小) 是您想要的.这将为您提供一个python字符串缓冲区，其内存内容位于指针的地址处.这应该适合传递给 Image.fromstring 或 pygame.image.frombuffer .

这篇关于python中的用户指针的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！