OpenCV setTrackbarPos_0

setTrackbarPos_0 sets the current position (the thumb) of a trackbar in an OpenCV HighGUI window. Out of the three "move a slider" nodes this pack generates, this is the one that at least does something visible - if there's a window to look at.

It wraps cv2.setTrackbarPos(trackbarname, winname, pos), which repositions an existing slider to a given value. Inputs are as you'd expect: trackbarname (STRING), winname (STRING), and pos (INT, the new position). Output is None - named unknown in the schema because the function returns nothing. It's a pure side-effect node; you drop it in the graph and nothing comes out of it.

The honest context: this family of HighGUI nodes exists because the pack auto-generates every standalone cv2 function, and window/trackbar functions didn't get filtered out. In a normal ComfyUI setup - especially headless, or remote - there are no HighGUI windows. setTrackbarPos can't position a slider in a window that was never created. On a desktop ComfyUI with a display you could build the full stack (named window, trackbar, this node), but that's an unusual way to work when ComfyUI's own widgets give you sliders that actually persist in the UI and get saved with your workflow.

So the honest recommendation: if this node showed up in a workflow you downloaded, it's scaffolding from someone who was experimenting with live OpenCV windows, and you can remove it. Its None output means nothing downstream depends on it. If your actual goal is tweaking a value interactively, use a regular node's number input or a primitive - those are first-class ComfyUI citizens and don't need a display attached to the server.

The usual pack gotchas apply to installing it: ComfyUI Manager → search "opencv-comfyui", or git clone https://github.com/geroldmeisinger/opencv-comfyui into ComfyUI/custom_nodes and restart. It needs opencv-contrib-python; numpy and torch come with ComfyUI. And the classic startup failure - Cannot import name 'guidedFilter' from 'cv2.ximgproc' - means two OpenCV installs are fighting; uninstall the extra.

Worth one more sentence on the trio: setTrackbarPos_0 moves the thumb, setTrackbarMin_0 and setTrackbarMax_0 bound the range. If you ever need all three, you're doing live desktop OpenCV debugging - and that's the only world in which they earn their place. Everywhere else, treat them as pack completeness, not as tools you'll reach for.