OpenCV startWindowThread_0

This is the oddest node in the pack, and I say that with affection. startWindowThread_0 takes no inputs, returns a single INT, and all it does is call cv2.startWindowThread() - OpenCV's HighGUI function that starts the GUI's background window thread on platforms that need one (mainly Linux, where Qt-backed imshow windows otherwise don't repaint properly).

Why does this exist in a ComfyUI pack at all? Because opencv-comfyui is auto-generated from OpenCV's type stubs, and it wraps every top-level standalone function - including the desktop GUI ones. So the generator dutifully turned "start a GUI window thread" into a node you can drop on a canvas. The only real partner for it is this pack's imshow_0 node, which calls cv2.imshow to pop a native OpenCV window on your desktop. If you're running ComfyUI locally with a display and you genuinely want a raw OpenCV preview window, wiring startWindowThread_0 before your imshow calls makes the window update behave. If you're running ComfyUI headless, on a server, or over SSH, this node does absolutely nothing useful - there's no display, no window, and the INT it returns (0, from a successful call) is meaningless to everything downstream.

Honestly? Skip it. For previews you're much better off with ComfyUI's own Save/PreviewImage or Nparrays2Image into a preview node. The auto-generation is the reason this node exists, and the auto-generation is also the reason you shouldn't feel obligated to use every node it produces. Some of them are infrastructure; some of them are noise. This is the latter.

Setup, for completeness. ComfyUI Manager → search "opencv-comfyui", or:

cd ComfyUI/custom_nodes
git clone https://github.com/geroldmeisinger/opencv-comfyui

restart. It needs opencv-contrib-python, numpy, torch. If you only ever touch this node, you can even skip the opencv requirement warning that comes with the rest of the pack - but you can't skip the conflict fix if you ever see Cannot import name 'guidedFilter' from 'cv2.ximgproc' (that's two OpenCV wheels fighting, and it breaks startup).

One honest note: there's no startWindowThread_1 variant in the brief, and there's no hidden functionality in the _0 suffix - it's just the first (and here, only) overload of the function the generator found. The pack is auto-generated, author-frankly-labelled "Expect dragons!", and you've just met one of the dragon-shaped bits. Rest easy and keep it out of your workflow.