title: adding labels to genes or segments with ggbio and geom_alignment
body: <p>I'm trying to use geom_alignment in the ggbio package to plot a stretch of genes, and I want to show labels under each gene.  The docs for geom_alignment say that this is done by specifying label = TRUE, and supplying a vector of labels in names.expr.  The problem is that it doesn't seem to work, and it's not throwing any error messages that might hold a clue.</p>
  <pre><code>  gr &lt;- GRanges(seqnames=&quot;test&quot;,
        IRanges(start=c(10,40,60),
        end=c(25,55,70),
        names=c(&quot;A&quot;,&quot;B&quot;,&quot;C&quot;),
        group = &quot;groupA&quot;)
      )
  
  ggplot(gr) + geom_alignment(aes(fill=group,col=group), gap.geom = &quot;segment&quot;, label = TRUE,names.expr = names(gr))
  </code></pre>
  <p><a href="https://i.stack.imgur.com/vSC3j.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vSC3j.png" alt="enter image description here" /></a></p>
  <p>So it plots the segments exactly as expected, but leaves off the labels.  Am I missing something here?</p>
  <p>There is an earlier question similar to this:
  <a href="https://stackoverflow.com/questions/31258616/adding-labels-to-individual-genes-with-ggbio-and-ggplot2">Adding Labels to Individual Genes with ggbio and ggplot2</a></p>
  <p>the suggested answer there involves splitting the GRanges object on the group variable before plotting, but I need to keep the parts of the GRanges object together, and at any rate this fix doesn't seem to be working as suggested.</p>
  <p>here is my session info:</p>
  <pre><code>R version 4.1.2 (2021-11-01)
  Platform: x86_64-pc-linux-gnu (64-bit)
  Running under: Ubuntu 20.04.3 LTS
  
  Matrix products: default
  BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
  LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0
  
  Random number generation:
   RNG:     Mersenne-Twister 
   Normal:  Inversion 
   Sample:  Rounding 
   
  locale:
   [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
   [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C                 
   [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
  
  attached base packages:
  [1] stats4    stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
   [1] ggbio_1.42.0         stringr_1.4.0        gplots_3.1.1         rtracklayer_1.54.0   ggplot2_3.3.5       
   [6] GenomicRanges_1.46.1 GenomeInfoDb_1.30.0  IRanges_2.28.0       S4Vectors_0.32.3     BiocGenerics_0.40.0 
  [11] dplyr_1.0.7          readr_2.1.0          vcfR_1.12.0          ballgown_2.26.0  
  </code></pre>