OpenCV arrowedLine_0

If you're building a workflow that explains itself - pointing at the face a detector found, showing a motion direction, marking a crop origin - you need arrows, and ComfyUI core doesn't give you a friendly one. arrowedLine_0 is OpenCV's cv2.arrowedLine wrapped as a node: draw a line with an arrowhead on an image. It's a drawing primitive, nothing fancy, and it's the kind of node you keep on hand for annotating outputs before you save them.

It comes from opencv-comfyui, the auto-generated pack of OpenCV wrappers. The author's own framing is "these nodes are ugly and complex to use, expect dragons" - and this one earns a little of that, because the coordinates and colors arrive as string literals you have to type just right.

The inputs, and the one that bites

• img - the image to draw on, as an NPARRAY. Note OpenCV draws in place: the output nparray is the image with the arrow painted on.
• pt1 / pt2 - the arrow's start and end, typed as Python-literal strings: "(30, 40)". Coordinates are (x, y).
• color - also a string literal, but in BGR, because this is OpenCV: "(0, 0, 255)" is red. If your arrow comes out blue when you asked for red, this is why.
• thickness - line thickness in pixels (int).
• line_type - line drawing mode. 4 and 8 are the classic 4/8-connected line algorithms; 16 is anti-aliased (LINE_AA), which is the one you want for nice-looking output.
• shift - fractional-pixel precision shift, almost always 0 for beginners.
• tipLength - the arrowhead size as a fraction of the line length (0–1). 0.1 is a sensible starting point; OpenCV's default is 0.1 too.
• Output: one nparray, the annotated image.

The gotcha is the literals. These widgets are parsed with Python's ast.literal_eval, so the exact syntax matters: "(30, 40)" works, "30, 40" also happens to work, but "(30, 40" or "30 40" throws the pack's signature invalid syntax (<unknown>, line 0) error. If you see that, check your parens before anything else.

Wiring it up

In: Image2Nparray (remember, the pack speaks OpenCV arrays, not Comfy IMAGE). Out: Nparrays2Image to preview or save. Everything is BGR inside the pack, so cvtColor (code 4 = BGR2RGB) is a legit middle step if you're composing with other ComfyUI nodes that expect RGB.

Install

ComfyUI Manager → search opencv-comfyui, or:

cd ComfyUI/custom_nodes
git clone https://github.com/geroldmeisinger/opencv-comfyui
pip install opencv-python-contrib

Restart ComfyUI. No model downloads. The pack's only setup trap is conflicting OpenCV installs (Cannot import name 'guidedFilter' from 'cv2.ximgproc') - reinstall cleanly if it bites.

One more thing: arrowedLine_1 is this node's identical twin (the generator made two wrappers from OpenCV's MatLike/UMat overloads). Either works; don't overthink the badge number.