perf(annotators): skip corner circles when drawing square label backgrounds

[kounelisagis]

What

Both rounded-rectangle helpers (LabelAnnotator.draw_rounded_rectangle and the public draw_rounded_rectangle in draw/utils) always drew two rectangles plus four corner circles, even when border_radius is 0. Zero is the default for LabelAnnotator and VertexLabelAnnotator, so the common case paid for six cv2 calls per label per frame where one fill rectangle does the same thing (the four circles are zero-radius no-ops, and one of the two rectangles already covers the whole box).

This adds a square-corner fast path to both helpers: when border_radius <= 0, draw a single fill rectangle and return. The radius > 0 path is untouched.

Impact

I profiled a typical 1080p frame with 100 labels and _draw_labels was the hottest part of the annotation, with 40k zero-radius circle calls. With the fast path:

• LabelAnnotator at 1080p, 100 labels: ~2.1 ms to ~1.3 ms per frame (about 1.6x), best of 7 runs
• the rounded-rectangle call itself at radius 0: ~2.8x faster in isolation
• VertexLabelAnnotator benefits too, since it uses the shared draw/utils helper

Output is pixel identical, verified against develop for LabelAnnotator, VertexLabelAnnotator, and draw_rounded_rectangle at both radius 0 and radius > 0.

I kept the two helpers separate rather than merging them: they take different inputs (xyxy tuple plus BGR vs Rect plus Color), and routing one through the other would add per-label object allocation in exactly the hot path this speeds up.

Tests

Added tests pinning the square output to a plain rectangle for both helpers, plus a rounded case that checks corners are actually cut. The public draw_rounded_rectangle had no tests before this.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82%. Comparing base (09b2199) to head (bd2b80f).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2346   +/-   ##
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- Coverage       82%     82%   -0%     
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  Files           68      68           
  Lines         9560    9566    +6     
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- Hits          7881    7880    -1     
- Misses        1679    1686    +7     

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[Copilot]

Pull request overview

This PR optimizes rounded-rectangle drawing in annotators and draw utilities by adding a fast path for the common border_radius <= 0 case, reducing unnecessary OpenCV calls while keeping output identical.

Changes:

• Added a square-corner fast path in both draw_rounded_rectangle helpers when border_radius <= 0.
• Added unit tests covering square-corner equivalence (radius 0 and negative) for both helpers.
• Added a test asserting that positive radius actually rounds corners.

Review Scores (n/5):

• Code quality: 5/5
• Testing: 5/5
• Documentation: 4/5

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/supervision/draw/utils.py	Adds early-return square-corner rectangle fill when border_radius <= 0 to avoid extra cv2 calls.
src/supervision/annotators/core.py	Adds the same fast path to LabelAnnotator.draw_rounded_rectangle for the hot per-label background draw.
tests/draw/test_utils.py	New tests for draw/utils.draw_rounded_rectangle square behavior and a positive-radius rounding assertion.
tests/annotators/test_core.py	Adds a regression test ensuring LabelAnnotator.draw_rounded_rectangle matches a plain filled rectangle for non-positive radius.

[Borda]

@kounelisagis, could you pls add visualization before and after? 🦝

[kounelisagis]

@kounelisagis, could you pls add visualization before and after? 🦝

Sure! Here is before (develop) vs after (this PR), for both the square default and a rounded radius, with an amplified diff on the right:

Top row is border_radius=0 (the default), bottom row is border_radius=25. The diff panel is absdiff x20, so any change would light up; it stays fully black in both cases. Output is pixel identical (max abs diff = 0) for square and rounded alike. The square path now draws one filled rectangle instead of two rectangles plus four zero-radius corner circles, and the rounded path is untouched.

How it was generated

import numpy as np, supervision as sv

scene = np.zeros((360, 640, 3), np.uint8)
scene[:] = np.linspace(40, 120, 640)[None, :, None].astype(np.uint8)
det = sv.Detections(
    xyxy=np.array([[40, 40, 200, 150], [260, 60, 460, 180],
                   [120, 210, 360, 330], [420, 210, 600, 320]], float),
    confidence=np.array([0.91, 0.86, 0.78, 0.69]),
    class_id=np.array([0, 1, 2, 1]),
    data={"class_name": np.array(["person", "car", "dog", "car"])},
)
box = sv.BoxAnnotator(thickness=2)
for radius in (0, 25):
    lab = sv.LabelAnnotator(border_radius=radius, text_scale=0.7, text_padding=8)
    img = lab.annotate(box.annotate(scene.copy(), det), det)

Run on develop and on this branch, then compare with cv2.absdiff (max abs diff is 0 in both cases).