LineStrips3D ignores color if num_strips divisible by four or equals three

[eskjorg]

Describe the bug
rr.LineStrips3D(strips, colors) ignores the colors argument and makes all lines white if len(strips) % 4 = 0 or len(strips) == 3.

To Reproduce

strips = [[[0, 0, 0], [0, 0, 1]]]
colors = [0x00FF00FF] # green
for n in range(30):
    rr.log(
        "linestrips3d", rr.LineStrips3D(strips=n * strips, colors=n * colors)
    )

Desktop (please complete the following information):

• OS: macOS Sequoia 15.1

Rerun version
Local client: rerun-cli 0.18.2 [rustc 1.76.0 (07dca489a 2024-02-04), LLVM 17.0.6] aarch64-apple-darwin release-0.18.2 59ff15b, built 2024-08-29T13:55:42Z

[Wumpf]

wow. that's.. impressive Oo. Thank you so much for filing!

Repros cleanly on main. It's an SDK issue given that the data doesn't get through. Given how language dependent our serialization is, I strongly suspect it's a Python SDK only issue.

Bad frame:

Good frame:

(edit: mixed up good/bad)

[eskjorg]

wow. that's.. impressive Oo. Thank you so much for filing!

Repros cleanly on main. It's an SDK issue given that the data doesn't get through. Given how language dependent our serialization is, I strongly suspect it's a Python SDK only issue.

Good frame: ...
Bad frame: ...

Thanks @Wumpf for jumping on this fast!

Also, I think you mixed up "good" and "bad" there.

[jleibs]

This is a bug in rgba32_ext.py. Confirmed it affects other primitives such as Points3D.

In short, the python API is trying to be way too clever with precedence of multi-representation of colors combined with our lazy batch-conversion.

Concretely consider we support:

• color = int (0x00ff00)
• color = [int] ([0, 255, 0] or [0, 255, 0, 255])
• colors = [color1, color2, color3, color4] ([0x00ff00, 0x00ff00, 0x00ff00, 0x00ff00], ...)
• colors = color ([0, 255, 0, 255], ...)

It's clear there's an ambiguity between an array of colors represented as ints, and a single RGBA represented as an array.

[jleibs]

fwiw, we actually try to handle this ambiguity here, but you need to be explicit about your types.
https://github.com/rerun-io/rerun/blob/jleibs/rrdp_wheels/rerun_py/rerun_sdk/rerun/datatypes/rgba32_ext.py#L76

Confirmed this works around the issue:

import rerun as rr
import numpy as np

rr.init("rerun_example_colorbad", spawn=True)

point = [[0, 0, 0]]
colors = [0x00FF00FF]  # green


for n in range(30):
    colors = np.array(n * colors, dtype=np.uint32)
    rr.log("points3d", rr.Points3D(positions=n * point, colors=colors))

[eskjorg]

Thanks @jleibs for the help!