CV Draw Polygon

Why you'd reach for this

Two jobs in one node. The obvious one: draw an outline through a point list - a projected object outline, a document quadrilateral after rectification, a rotated detector's quads. The less obvious, more useful one: set thickness to 0 and it fills instead, which turns a polygon into a mask. Rotated text quads, a quadrilateral you found with CV Find Quadrilateral, any N-corner region - filled into a MASK primitive, no thresholding involved.

That's the mask-creation path in this pack: geometry in, filled region out. It's a deterministic alternative to painting or segmenting a region by hand.

How it works

(N, 2) input means one polyline or polygon through N points. (N, M, 2) means N separate M-point polygons - which is exactly the shape CV EAST Text Detect emits for its rotated text quads, so one node draws a whole page of text boxes.

closed connects the last point back to the first. When thickness = 0, filling happens via cv2.fillPoly and both closed and line_style are ignored (a filled polygon is always closed). The fill value is taken from the blue component on a single-channel canvas, since that's the only channel a MASK has.

Non-solid line_style values - dashed, dotted, dash-dot - go through the pack's own dash walker, because cv2 has no stroke pattern at all: segments are walked by arc length and stamped as short solid pieces, with the positions kept in float until each piece is placed so the pattern doesn't drift along a long edge. Same tool as the contour and path nodes, same reason for existing: colour alone can't separate two overlaid line sets for a colour-blind viewer or in greyscale, so two outlines on one image should differ in style, not just in hue.

One more trick from the node's own description, and it's a good one: to draw conditionally - only when CV Find Homography reports found = true, say - select between this node's output and the untouched image with a control-flow node such as Basic Data Handling's if/else. Its lazy inputs skip the drawing branch entirely when it isn't taken, so nothing runs and nothing is drawn.

Under 2 points raises: you can't draw a line through one point, and the error names the array shape you passed.

Inputs and outputs that matter

• points - (N,2) for one polygon, (N,M,2) for many. This is the input to get right; everything else is cosmetic.
• thickness - pixels, or 0 for filled. The mask-making switch.
• closed - closed polygon vs open polyline. Ignored when filling.
• color - single value or BGR tuple. On a MASK canvas use a single value; '(0, 0, 255)' keeps only the blue component.
• line_style (optional) - the dash patterns, ignored when filled.
• image - the only output, same format as the source.

Install

cd ComfyUI/custom_nodes
git clone https://github.com/bmad4ever/comfyui_cv
pip install "opencv-contrib-python-headless~=5.0.0.93"

Python ≥ 3.12 and a recent ComfyUI (V3 node API), or install ComfyUI CV via ComfyUI Manager. Pure CPU cv2; no model, no GPU.

Common issues

• "Need at least 2 points" - the array came out with fewer than two rows, usually because an upstream detector found nothing and the filtering pipeline emptied it. Guard it with the thing's found flag.
• Filled output is black/white with no outline. That's thickness = 0 doing what it says: filled, no stroke. If you want both, run the node twice.
• Only one of several polygons drawn. Your array is (N,2) when you meant (N,M,2) - the node flattens and draws one polyline through everything. Nested shapes can't be expressed in two dimensions plus a count; the three-dimensional form is the one you want.
• Outline invisible on a MASK. BGR tuple on a single channel. Use '255'.
• Contrib build. Installing a non-contrib OpenCV wheel over the contrib one empties the shared site-packages/cv2 contrib submodules; nodes backed by contrib APIs then vanish from the pack. tools/repair_opencv_contrib.py --check / --apply.