几何函数内部的OpenLayers要素样式zIndex

Question

This (silly) picture summarizes the issue I'm having:

These are rendered in a vector layer.

Below these shields is a line string that I render once as-is (ie as a line), and on top of it I also render it using a style that has a geometry function defined. In that function, I return a ol.geom.MultiPoint containing the coordinates where I want shields to be added alongside the line.

My above demonstration is silly, I know (ie in my real use case, the gap between the shields is way bigger, so I know I won't have any collision).

The thing is, I'm aware that there's normally a way to avoid this kind of behaviour with the zIndex property of the ol.style.Style , ie if each feature has its own style defining a different zIndex, then each shield+text would be correctly rendered with text below overlapping shields. But, this can't work with a geometry method, as the same style is used multiple times for the same feature to render it multiple times.

Like I said, since I'll define a big enough gap to avoid collisions anyway I don't really need to figure a way to fix this issue, but I'm curious if there is one, for my future self and other people that would like to know.

Answer 1

Each point on a multipoint can be given its own style. Take this OpenLayers example http://openlayers.org/en/v4.6.5/examples/polygon-styles.html If you replace the styles array with this function each point on the multipoints can be given a different radius and different shade of yellow. It also works for zIndex, as can be seen where the first and last coordinates of the polygons coincide.

function styles(feature) {

  var multipoint = new ol.geom.MultiPoint(feature.getGeometry().getCoordinates()[0]);

  var styles = [

    new ol.style.Style({
      stroke: new ol.style.Stroke({
        color: 'blue',
        width: 3
      }),
      fill: new ol.style.Fill({
        color: 'rgba(0, 0, 255, 0.1)'
      })
    })

  ];

  multipoint.getCoordinates().forEach(function(coordinates, index) {

    var shade = (index+1)*50;
    var radius = (index+1)*5;
    var zIndex = 10-index;
    styles.push(new ol.style.Style({
      zIndex: zIndex,
      image: new ol.style.Circle({
        radius: radius,
        fill: new ol.style.Fill({
          color: 'rgba(' + shade + ',' + shade + ', 0, 1)'
        })
      }),
      geometry: new ol.geom.Point(coordinates)

    }));

  });

  return styles;
}