where can i find a thorough description of implementing custom ol.style.Style in openlayers 3?

问题

I've read through the source, and looked at the examples but haven't found the answer yet.

I need to style the image that appears on the modify overlay beneath the mouse cursor.

i'm using a custom style function to add midpoints and custom endpoints to the layer used by ol.interaction.Modify. ol.interaction.Modify is applying styling to a point near the mouse cursor to indicate that the feature can be modified. This is great except the cursor styling falls beneath the custom endpoints. i can't find a way to alter the z-index.

回答1:

so, i'm answering my question for myself. i guess that's what makes the internet wonderful. i'm not a dog.

// we'd normally pass feature & resolution parameters to the function, but we're going to
// make this dynamic, so we'll return a style function for later use which will take those params.

DynamicStyleFunction = ( function( /* no feat/res yet!*/ ) {

  /**
   you really only get style are rendered upon simple geometries, not features. features are made of different geometry types, and styleFunctions are passed a feature that has its geometries rendered.  in terms of styling vector geometries, you have only a few options. side note: if there's some feature you expect to see on the the map and it's not showing up, you probably haven't properly styled it. Or, maybe it hasn't been put it in a collection that is included in the source layer... which is a hiccup for a different day.
  */

  // for any geometry that you want to be rendered, you'll want a style. 
  var styles = {};
  var s = styles;

 /**
   an ol.layer.Vector or FeatureOverlay, renders those features in its source by applying Styles made of Strokes, Fills, and Images (made of strokes and fills) on top of the simple geometries which make up the features

   Stroke styles get applied to ol.geom.GeometryType.LINE_STRING

   MULTI_LINE_STRING can get different styling if you want

  */

  var strokeLinesWhite =   new ol.style.Stroke({ 
      color:  [255, 255, 255, 1], // white
      width:  5,
    })

  var whiteLineStyle  new ol.style.Style({
    stroke: strokeLinesWhite
  })

  styles[ol.geom.GeometryType.LINE_STRING] = whiteLineStyle

  /** 
    Polygon styles get applied to ol.geom.GeometryType.POLYGON

    Polygons are gonna get filled. They also have Lines... so they can take stroke

  */

  var fillPolygonBlue = new ol.style.Style({
    fill:  new ol.style.Fill({
      color: [0, 153, 255, 1], // blue
    })
  })

  var whiteOutlinedBluePolygon = new ol.style.Style({
    stroke: strokeLinesWhite,
    fill:   fillPolygonBlue,
  })

  styles[ol.geom.GeometryType.POLYGON] = fillPolygonBlue

  /** 
    Circle styles get applied to ol.geom.GeometryType.POINT

    They're made with a radius and a fill, and the edge gets stroked... 

  */

  var smallRedCircleStyle = new ol.style.Style({ 
    image: new ol.style.Circle({
      radius: 5,
      fill: new ol.style.Fill({
        color: '#FF0000', // red... but i had to look it up
      })
    })
  })

  var whiteBigCircleWithBlueBorderStyle = new ol.style.Style({ 
    image: new ol.style.Circle({
      radius: 10,
      fill: new ol.style.Fill({
        color: '#FFFFFF' // i guessed it
      })
    }),
    stroke: new.ol.style.Stroke({
      color: '#0000FF',  // blue
      width: 5
    })
  })

  // render all points as small red circles
  styles[ol.geom.GeometryType.POINT] = smallRedCircleStyle


  // if you pass an array as the style argument, every rendering of the feature will apply every defined style style rendered with the geometry as the argument. that can be a whole lot of rendering in a FeatureOverlay... 

  smallRedCircleStyle.setZIndex(Infinity)
  whiteBigCircleWithBlueBorderStyle.setZIndex(Infinity -1) // that prob wouldn't work, but i hope it's instructive that you can tinker with styles

  // so... 
  var bullseyePointStyle = [ smallRedCircleStyle, whiteBigCircleWithBlueBorderStyle ];

  return function dynamicStyleFunction (feature, resolution){

    // this is the actual function getting invoked on each function call
    // do whatever you want with the feature/resolution.

    if (Array.indexOf(feature.getKeys('thisIsOurBullseyeNode') > -1) {
      return bullseyePointStyle
    } else if (feature.getGeometryName('whiteBlueBox')){
      return whiteOutlinedBluePolygon
    } else {
      return styles[feature.getGeometryName()]
    }
  }
})()

回答2:

ol.interaction.Modify, ol.interaction.Select and ol.interaction.Draw take a style argument to change the look of the sketching features.

来源：https://stackoverflow.com/questions/30268100/where-can-i-find-a-thorough-description-of-implementing-custom-ol-style-style-in