highlighting directly adjacent vertices fails with error

[dfsp-spirit]

Describe the bug

Trying to highlight 2 adjacent vertices using the function highlight.vertices.on.subject.spheres() leads to the following error message:

Error in rgl.material(...) : There must be at least one color
In addition: Warning messages:
1: In coloredmesh.from.color(subjects_dir, subject_id, color_data$rh,  :
  Data mismatch: surface has 163842 vertices, but 0 color values passed in argument 'color_data'.

2: In fs.coloredmesh(mesh, color_data, hemi, metadata = metadata) :
  The mesh3d instance from parameter 'mesh' has 163842 vertices, but 0 colors passed in parameter 'col'.

3: In cbind(x, 1) :

 Error in rgl.material(...) : There must be at least one color 

To Reproduce

devtools::install_github('dfsp-spirit/fsbrain', ref="geodesic");
fsbrain::download_optional_data();
    fsbrain::download_fsaverage(accept_freesurfer_license = TRUE);
    subjects_dir = fsbrain::get_optional_data_filepath("subjects_dir");
    subject_id = 'fsaverage';

    vertices = c(32258, 171); # These are directly adjacent
    highlight.vertices.on.subject.spheres(subjects_dir, subject_id, vertices = vertices);

Expected behavior The 2 vertices get highlight in a plot.

Screenshots none

Environment:

• Operating System [e.g. MacOS10.13, or Ubuntu 20.04]: Ubuntu 20.04
• R version (output of R --version in system shell): 3.6.3
• fsbrain version (output of packageVersion('fsbrain') in R): 0.5.0-dev (unsupported)

Additional context Add any other context about the problem here.

[dfsp-spirit]

It turned out that this issue was not related to the vertices being adjacent. The problem was that there was no vertex to highlight for one hemi, leading to all-NA per-vertex data, leading to an empty color value vector (per-vertex colors) for the coloredmesh.

This has been fixed in 93d0c57 by setting the color to white if 0 colors are passed (with a warning).