Add Helix to demo.rerun.io (#2930)

What the title says.

Didn't rename the `dna` folder on purpose: not particularly looking to
deal with broken links all over the place today :)

### What

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/2930) (if
applicable)

- [PR Build Summary](https://build.rerun.io/pr/2930)
- [Docs preview](https://rerun.io/preview/pr%3Acmc%2Fhelix_demo/docs)
- [Examples
preview](https://rerun.io/preview/pr%3Acmc%2Fhelix_demo/examples)

examples/python/dna/main.py

@@ -6,44 +6,54 @@
 """
 from __future__ import annotations
 
-import sys
+import argparse
 from math import tau
 
 import numpy as np
 import rerun as rr  # pip install rerun-sdk
 from rerun_demo.data import build_color_spiral
 from rerun_demo.util import bounce_lerp, interleave
 
-# sanity-check since all other example scripts take arguments:
-assert len(sys.argv) == 1, f"{sys.argv[0]} does not take any arguments"
 
-rr.init("DNA Abacus")
+def log_data() -> None:
+    rr.set_time_seconds("stable_time", 0)
 
-rr.spawn()
-rr.set_time_seconds("stable_time", 0)
+    NUM_POINTS = 100
 
-NUM_POINTS = 100
+    # points and colors are both np.array((NUM_POINTS, 3))
+    points1, colors1 = build_color_spiral(NUM_POINTS)
+    points2, colors2 = build_color_spiral(NUM_POINTS, angular_offset=tau * 0.5)
+    rr.log_points("helix/structure/left", points1, colors=colors1, radii=0.08)
+    rr.log_points("helix/structure/right", points2, colors=colors2, radii=0.08)
 
-# points and colors are both np.array((NUM_POINTS, 3))
-points1, colors1 = build_color_spiral(NUM_POINTS)
-points2, colors2 = build_color_spiral(NUM_POINTS, angular_offset=tau * 0.5)
-rr.log_points("dna/structure/left", points1, colors=colors1, radii=0.08)
-rr.log_points("dna/structure/right", points2, colors=colors2, radii=0.08)
+    points = interleave(points1, points2)
+    rr.log_line_segments("helix/structure/scaffolding", points, color=[128, 128, 128])
 
-points = interleave(points1, points2)
-rr.log_line_segments("dna/structure/scaffolding", points, color=[128, 128, 128])
+    time_offsets = np.random.rand(NUM_POINTS)
+    for i in range(400):
+        time = i * 0.01
+        rr.set_time_seconds("stable_time", time)
 
-time_offsets = np.random.rand(NUM_POINTS)
-for i in range(400):
-    time = i * 0.01
-    rr.set_time_seconds("stable_time", time)
+        times = np.repeat(time, NUM_POINTS) + time_offsets
+        beads = [bounce_lerp(points1[n], points2[n], times[n]) for n in range(NUM_POINTS)]
+        colors = [[int(bounce_lerp(80, 230, times[n] * 2))] for n in range(NUM_POINTS)]
+        rr.log_points("helix/structure/scaffolding/beads", beads, radii=0.06, colors=np.repeat(colors, 3, axis=-1))
 
-    times = np.repeat(time, NUM_POINTS) + time_offsets
-    beads = [bounce_lerp(points1[n], points2[n], times[n]) for n in range(NUM_POINTS)]
-    colors = [[int(bounce_lerp(80, 230, times[n] * 2))] for n in range(NUM_POINTS)]
-    rr.log_points("dna/structure/scaffolding/beads", beads, radii=0.06, colors=np.repeat(colors, 3, axis=-1))
+        rr.log_transform3d(
+            "helix/structure",
+            rr.RotationAxisAngle(axis=[0, 0, 1], radians=time / 4.0 * tau),
+        )
 
-    rr.log_transform3d(
-        "dna/structure",
-        rr.RotationAxisAngle(axis=[0, 0, 1], radians=time / 4.0 * tau),
-    )
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="Logs rich data using the Rerun SDK.")
+    rr.script_add_args(parser)
+    args = parser.parse_args()
+
+    rr.script_setup(args, "DNA Abacus")
+    log_data()
+    rr.script_teardown(args)
+
+
+if __name__ == "__main__":
+    main()

scripts/ci/build_demo_app.py

@@ -265,6 +265,13 @@ def main() -> None:
         """,
         "build_args": [],
     },
+    "dna": {
+        "title": "Helix",
+        "description": """
+        Simple example of logging line primitives to draw a 3D helix.
+        """,
+        "build_args": [],
+    },
 }
 
 if __name__ == "__main__":