Displacement type pile with overlaying tracks does not work

[ThHarbig]

When adding "alignment": "overlay" while using "displacement": {"type": "pile"} the displacement no longer works (see demo) Replacing it with a dataTransform is a work-around:

          "dataTransform": [
            {
              "type": "displace",
              "method": "pile",
              "boundingBox": {
                "padding": 3.5,
                "startField": "start",
                "endField": "end"
              },
              "newField": "row"
            }
          ],
          "row": {"field": "row", "type": "nominal"},

This also fixes the slightly buggy piling that is visible when using "displacement": {"type": "pile"}

[sehilyi]

Gosling currently supports displacement in two ways, i.e., (1) displacement and (2) displace Data Transform. Having these two options make processing specs more complicated, so I wonder if it makes sense to remove the former option and provide a single method for users.

interface SingleTrackBase extends CommonTrackDef {
    ...
-    // Resolving overlaps
-    displacement?: Displacement;
}

The original purpose for adding the former option was to support an easier way to use displacement. (1) displacement

"displacement": {"type": "pile"} // internally add `displace` `dataTransform`  based on spec (e..g, x, xe) and add `row` channel when processing the spec

(2) displace dataTransform

          "dataTransform": [
            {
              "type": "displace",
              "method": "pile",
              "boundingBox": {
                "padding": 3.5,
                "startField": "start",
                "endField": "end"
              },
              "newField": "row"
            }
          ],
          "row": {"field": "row", "type": "nominal"},

cc @manzt @etowahadams

[ThHarbig]

Somehow related to piling issues: In the example below ~~(sorry for the weird link, GitHub will somehow not format it properly)~~ the piling is off and the points are not placed on the axis although there would be enough space. I initially thought it would be because I set startField and endField to the same value, but if I do this with the example in the original post it works fine.

demo

[ThHarbig]

Thank you for the fix @sehilyi, I am adapting the IslandViewer example now. Can I pile from bottom to top instead of top to bottom (or inner circle/outer circle in circular layout) as well?

[sehilyi]

The y channel supports flipping, so I think you can replace the row with with y channel and then use the flip option.

{
      "style": {"outlineWidth": 1, "outline": "black"},
      "data": {
        "url": "https://s3.amazonaws.com/gosling-lang.org/data/IslandViewer/NC_004631.1_annotations.csv",
        "type": "csv",
        "genomicFields": ["Gene start", "Gene end"]
      },
      "dataTransform": [
        {
          "type": "displace",
          "method": "pile",
          "boundingBox": {
            "padding": 3.5,
            "startField": "Gene start",
            "endField": "Gene end"
          },
          "newField": "row"
        }
      ],
-      "row": {"field": "row", "type": "nominal"},
+      "y": {"field": "row", "type": "nominal", "flip": true},
      "mark": "point",
      "x": {"field": "Gene start", "type": "genomic"},
      "xe": {"field": "Gene end", "type": "genomic"},
      "size": {"value": 3},
      "color": {
        "field": "Type",
        "type": "nominal",
        "domain": ["Victors", "BLAST", "RGI", "PAG"],
        "range": ["#460B80", "#A684EA", "#FF9CC1", "#FF9CC1"]
      }
    },