added cv.CAP_DSHOW to cv.Videocapture to fix https://github.com/vlachoudis/bCNC/issues/1526

[ldpgh]

added cv.CAP_DSHOW to cv.Videocapture
fix issue: #1526
by answer: https://answers.opencv.org/question/234933

[ldpgh]

App-Test
(1) cv2+Py3.7.4 ... ok

>>python
Python 3.7.4 (tags/v3.7.4:e09359112e, Jul  8 2019, 19:29:22) [MSC v.1916 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2 as cv
>>> cv.__version__
'4.4.0'
>>> cam=cv.VideoCapture(0, cv.CAP_DSHOW)
>>> img=cam.read()
>>> print(img[1][0])
[[ 0 14 11]
 [ 0 15 12]
 [ 0 12 10]
 ...
 [ 5  7  1]
 [ 4  6  5]
 [ 4  6  5]]
>>> quit()
>>

(2) Py3.7.4+bCNC ... ok

(3) cv2+Py2.7.12 ... ok

>>python
Python 2.7.12 (v2.7.12:d33e0cf91556, Jun 27 2016, 15:19:22) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2 as cv
>>> cv.__version__
'4.2.0'
>>> cam=cv.VideoCapture(0, cv.CAP_DSHOW)
>>> img=cam.read()
>>> print(img[1][0])
[[ 8 10 10]
 [ 8 10 10]
 [ 4 11  9]
 ...,
 [ 6  8  9]
 [ 6  8  8]
 [ 4  6  6]]
>>> quit()
>>

(4) Py2.7.12+bCNC ... ok ... just checked CameronOn/VideoStream/CameraOff

[Harvie]

This does not seem very portable to me. You must understand that bCNC has lots of users running Linux, MacOS and perhaps even other operating systems.

By default the OpenCV selects the best available video backend. If OpenCV does not select the correct backend i beleive this is a bug in OpenCV and you should consult developers of OpenCV project. Hardcoding windows-based backend is simply not going to happen in bCNC.

[Harvie]

Oh and now i've read the #1526
It says the camera works but crashes after few moments. If there is crash caused by OpenCV, they should fix it.

[Harvie]

The proposed fix feels like it might mess up bCNC on Linux and OSX (not sure tho)
Is this still an issue with latest opencv? Maybe we can just increase the opencv version in setup.py

[Harvie]

cv.CAP_DSHOW reportedly breaks opencv at MacOS.

https://www.reddit.com/r/learnpython/comments/oxo3gd/why_do_i_have_to_use_cv2cap_dshow/