Only one qmlglsink possible if using windows

Submitted by hol..@..ob.com

Link to original bug (#796456)

Description

I use QT 5.9.1 on windows10 with an intel graphics card. Using one output sink is no problem.
Only adding multiple GstGLVideoItems doesn’t work.

I add the qmlqlsink to my qml file as follows:
GstGLVideoItem
{
id: idVideo0
objectName: "videoItem0"
x: 0
y: 0
width: parent.width / 2
height: parent.height / 2
Component.onCompleted: _AppMgr.vid0 = idVideo0
}
GstGLVideoItem
{
id: idVideo1
objectName: "videoItem1"
x: parent.width / 2
y: 0
width: parent.width / 2
height: parent.height / 2
Component.onCompleted: _AppMgr.vid1 = idVideo1
}

In C++ backend I wait till the vid0 and vid1 properties are set and then I start building the pipline.
Vid0 works as expected…. If I use the same pipeline with vid1 I get:

0:00:01.930173963 4088 cb23330 INFO glcontext gstglcontext.c:1231:gst_gl_context_create_thread:<glcontextwgl0> Attempting to create opengl context. user chosen api(s) (any), compiled api support (opengl opengl3) display api (opengl)
0:00:01.941723030 4088 cb23330 INFO glcontext gstglcontext.c:1242:gst_gl_context_create_thread:<glcontextwgl0> created context
0:00:01.941934098 4088 cb23330 INFO glcontext gstglcontext.c:1258:gst_gl_context_create_thread:<glcontextwgl0> available GL APIs: opengl
0:00:01.959707209 4088 cb23330 INFO glcontext gstglcontext.c:1071:_create_context_info:<glcontextwgl0> GL_VERSION: 4.5.0 - Build 22.20.16.4771
0:00:01.959846536 4088 cb23330 INFO glcontext gstglcontext.c:1074:_create_context_info:<glcontextwgl0> GL_SHADING_LANGUAGE_VERSION: 4.50 - Build 22.20.16.4771
0:00:01.959894111 4088 cb23330 INFO glcontext gstglcontext.c:1076:_create_context_info:<glcontextwgl0> GL_VENDOR: Intel
0:00:01.959931869 4088 cb23330 INFO glcontext gstglcontext.c:1078:_create_context_info:<glcontextwgl0> GL_RENDERER: Intel(R) HD Graphics 530
……..
Error: Could not initialize window system

Version: 1.12.4