Enable data-driven expressions for collision properties

[tristen]

Motivation

I have a use case for setting collision conditions to larger transit labels but defaulting to defaults for minor ones. Writing a data condition that effect these properties would help a lot:

• text-allow-overlap
• icon-allow-overlap
• icon-ignore-placement
• text-ignore-placement
• text-optional
• icon-optional
• text-padding
• icon-padding

Design Alternatives

Creating a new layer to handle overlap properties. When a layer is this long, its a lot to duplicate and keep in sync:

See transit-label layer in Streets v11

{
  "id": "transit-label",
  "type": "symbol",
  "metadata": { "mapbox:featureComponent": "transit-labels", "mapbox:group": "Transit labels" },
  "source": "composite",
  "source-layer": "transit_stop_label",
  "minzoom": 12,
  "filter": [
    "step",
    ["zoom"],
    [
      "all",
      ["match", ["get", "mode"], ["rail", "metro_rail"], true, false],
      ["!=", ["get", "stop_type"], "entrance"]
    ],
    15,
    [
      "all",
      ["match", ["get", "mode"], ["rail", "metro_rail", "ferry", "light_rail"], true, false],
      ["!=", ["get", "stop_type"], "entrance"]
    ],
    16,
    ["all", ["!=", ["get", "mode"], "bus"], ["!=", ["get", "stop_type"], "entrance"]],
    17,
    ["!=", ["get", "stop_type"], "entrance"],
    19,
    true
  ],
  "layout": {
    "text-size": 12,
    "icon-image": ["get", "network"],
    "text-font": ["DIN Offc Pro Medium", "Arial Unicode MS Regular"],
    "text-justify": ["match", ["get", "stop_type"], "entrance", "left", "center"],
    "text-offset": [
      "match",
      ["get", "stop_type"],
      "entrance",
      ["literal", [1, 0]],
      ["literal", [0, 0.8]]
    ],
    "text-anchor": ["match", ["get", "stop_type"], "entrance", "left", "top"],
    "text-field": [
      "step",
      ["zoom"],
      "",
      14,
      [
        "match",
        ["get", "mode"],
        ["rail", "metro_rail"],
        ["coalesce", ["get", "name_en"], ["get", "name"]],
        ""
      ],
      16,
      [
        "match",
        ["get", "mode"],
        ["bus", "bicycle"],
        "",
        ["coalesce", ["get", "name_en"], ["get", "name"]]
      ],
      18,
      ["coalesce", ["get", "name_en"], ["get", "name"]]
    ],
    "text-letter-spacing": 0.01,
    "text-max-width": ["match", ["get", "stop_type"], "entrance", 15, 9]
  },
  "paint": {
    "text-halo-color": "hsl(35, 17%, 100%)",
    "text-color": [
      "match",
      ["get", "network"],
      "tokyo-metro",
      "hsl(180, 50%, 30%)",
      "mexico-city-metro",
      "hsl(25, 100%, 100%)",
      ["barcelona-metro", "delhi-metro", "hong-kong-mtr", "milan-metro", "osaka-subway"],
      "hsl(0, 90%, 47%)",
      ["boston-t", "washington-metro"],
      "hsl(0, 0%, 0%)",
      ["chongqing-rail-transit", "kiev-metro", "singapore-mrt", "taipei-metro"],
      "hsl(140, 90%, 25%)",
      "hsl(230, 48%, 44%)"
    ],
    "text-halo-blur": 0.5,
    "text-halo-width": 0.5
  }
}