one concern that could be brought up is that some users have created infrastructure around svg being the default renderer. possibly, in that case, we would need to fork stuff in a (very) similar way to jbrowse 1 and make a CanvasFeatures track and an SvgFeatures track, which FeatureTrack being the default with svg renderer.

just for the record, this is definitely way faster === more pleasant to use imo. if there are considerations before pushing forward on this, feel free to add, but could be worth pushing over the finish line

from meeting just now, thinking about how to allow pluggable Glyphs.

two ways of doing this I can think of:

1. add a pluggable element type called a CanvasFeatureGlyphType, add it to the plugin manager, etc.
2. add an extension point called CanvasFeatures-chooseGlyph that lets people modify the code that chooses what glyph class to use

@cmdcolin is this still on the radar? I would like to configure something that looks like the chromHMM track in jbrowse2, e.g. see https://jbrowse.org/code/JBrowse-1.16.11/?data=sample_data%2Fjson%2Fvolvox&loc=ctgA%3A9898..32508&amp%3Btracks=DNA%2CTranscript%2Cvolvox-sorted-vcf%2Cvolvox-sorted_bam%2Cvolvox_microarray_bw_xyplot%2Cvolvox_microarray_bw_density&amp%3Bdata=sample_data%2Fjson%2Fvolvox&amp%3Bhighlight=&tracks=DNA%2CTranscript%2Cvolvox_microarray_bw_density%2Cvolvox_microarray_bw_xyplot%2Cvolvox-sorted-vcf%2CChromHMM&highlight=

@thomasvangurp Many of the JBrowse 1 CanvasFeatures renderer features are already available in our SvgFeatureRenderer in JBrowse 2. For example, here is a link to a JBrowse 2 session with an example of a track like the ChromHMM track you linked:

https://s3.amazonaws.com/jbrowse.org/code/jb2/main/index.html?config=test_data%2Fvolvox%2Fconfig.json&session=share-_dSWmP49dR&password=vGe4g.

Also, here is the configuration for that track:

{
  "type": "FeatureTrack",
  "trackId": "chromhmm",
  "name": "ChromHMM",
  "assemblyNames": [
    "volvox"
  ],
  "adapter": {
    "type": "BedAdapter",
    "bedLocation": {
      "locationType": "UriLocation",
      "uri": "https://s3.amazonaws.com/jbrowse.org/code/JBrowse-1.16.11/sample_data/raw/volvox/volvox_segment.bed"
    }
  },
  "displays": [
    {
      "type": "LinearBasicDisplay",
      "displayId": "chromhmm-LinearBasicDisplay",
      "renderer": {
        "type": "SvgFeatureRenderer",
        "color1": "jexl:get(feature,'name')=='1_TssA'?'red':get(feature,'name')=='2_TssAFlnk'?'pink':get(feature,'name')=='3_TxFlnk'?'purple':get(feature,'name')=='4_Tx'?'orange':get(feature,'name')=='5_TxWk'?'darkorange':get(feature,'name')=='6_EnhG'?'yellow':get(feature,'name')=='7_Enh'?'gold':get(feature,'name')=='8_ZNFRpts'?'blue':get(feature,'name')=='9_Het'?'darkgreen':get(feature,'name')=='10_TssBiv'?'green':get(feature,'name')=='11_BivFlnk'?'lightgreen':get(feature,'name')=='12_EnhBiv'?'purple':get(feature,'name')=='13_ReprPC'?'lightblue':get(feature,'name')=='14_ReprPCWk'?'salmon':get(feature,'name')=='15_Quies'?'lightgrey':black",
        "labels": {
          "name": ""
        },
        "displayMode": "collapse"
      }
    }
  ]
}

attempting to push this PR forward a bit, still wip but some updates

floating labels

This PR changes it so that all the labels are rendered separately from the features at the display level, aggregating across a variable called display.layoutFeatures

I made it so that the "floating labels" rendering is moved to what I might call a more "principled" approach

The current feature label rendering is done on a block by block basis, with a fair number of hacks to make it stay on the screen in a "floating way"

this separated rendering also makes font rendering separate from feature drawing, which allows us to use plain html divs for text rendering, which is generally looks better and less pixelated than canvas font rendering

collapsed introns

some motivation with the above floating label refactoring is that "collapsed intron" display is handled better. previously, the label rendering in "collapsed intron" scenarios (which have many displayedRegion boundaries) was glitchy. now pretty much seemless

main branch
https://jbrowse.org/code/jb2/main/?config=test_data%2Fconfig_demo.json&session=share-U3J3bEP-aC&password=ijHd0

this branch
https://jbrowse.org/code/jb2/add_canvas_feature_renderer/?config=test_data%2Fconfig_demo.json&session=share-U3J3bEP-aC&password=ijHd0

large region

when rendering large amounts of genes, the canvas renderer should be much faster and noticeably less laggy

main branch
https://jbrowse.org/code/jb2/main/?config=test_data%2Fconfig_demo.json&session=share-RuR3oRl-1K&password=ZbPd3

this branch
https://jbrowse.org/code/jb2/add_canvas_feature_renderer/?config=test_data%2Fconfig_demo.json&session=share-RuR3oRl-1K&password=ZbPd3