Openlayers 4 use canvas pattern for feature style

Question

I'm using latest OL 4 version. I have several features on the map (one company -> one feature). Each company has a category and each category has one color.

Style of feature

var style = new ol.style.Style({
    image: new ol.style.RegularShape({
        fill: new ol.style.Fill({color: color}),
        stroke: new ol.style.Stroke({ color: 'black', width: 2 }),
        points: 4,
        radius: 10,
        angle: Math.PI / 4
    })
});

Color is a simple string like: "green" or "blue". This is working fine.

But there are companies with more than one category (max 2). My idea was to use a canvas pattern:

var canvas = document.createElement('canvas');
canvas.width = 10;
canvas.height = 10;
var context = canvas.getContext('2d');
context.fillStyle = "black";
context.fillRect(0, 0, 5, 5);
context.fillStyle= "white";
context.fillRect(5,0,5,5);                        
color = context.createPattern(canvas, "no-repeat");

And then use this color for the style of the feature:

var style = new ol.style.Style({                
    fill: new ol.style.Fill({colorlike: color})
});

this didn't work so I tried to use it with image fill:

var style = new ol.style.Style({
    image: new ol.style.RegularShape({
        fill: new ol.style.Fill({colorlike: color})                   
    })
});

This didn't work either. color and colorlike won't work

How do I use a canvas pattern for a OL feature. I just want a rectangle with a different color each half. But I can't get it by the OL api or the examples, because they all use style on layer or image style, but not the exact way I need it...

Any ideas?

thanks in advance

Did you try doing two strokes with a width of 5? – Alexander Higgins Jul 08 '17 at 05:32 — Alexander Higgins, Jul 08 '17 at 05:32
How are you drawing your styles? – Alexander Higgins Jul 08 '17 at 05:41 — Alexander Higgins, Jul 08 '17 at 05:41

score 1 · Answer 1 · answered Jul 08 '17 at 06:08

You can work on getting your fill pattern correct, but here is a working example using a canvas generated pattern using a variety of shapes and two vector layers.

<!DOCTYPE html>
<html>
  <head>
    <title>Regular Shapes</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.2.0/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <script src="https://openlayers.org/en/v4.2.0/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script>
    /*var canvas = document.createElement('canvas');
canvas.width = 10;
canvas.height = 10;
var context = canvas.getContext('2d');
context.fillStyle = "black";
context.fillRect(0, 0, 5, 5);
context.fillStyle= "white";
context.fillRect(5,0,5,5);                        
color = context.createPattern(canvas, "no-repeat");*/

var canvas = document.createElement('canvas');
var context = canvas.getContext('2d');

var pixelRatio = ol.has.DEVICE_PIXEL_RATIO;
var pattern = (function() {
        canvas.width = 10;
        canvas.height = 10
        // white background
        context.fillStyle = 'white';
        context.fillRect(0, 0, 5, 5);
          context.fill();
        // outer circle
        context.fillStyle = 'black';
        context.fillRect(5, 5, 5, 5);
        context.fill();

        return context.createPattern(canvas, 'repeat');
      }());
    /*var vectorLayer = new ol.layer.Vector({
        source: new ol.source.Vector({
          url: 'https://openlayers.org/en/v4.2.0/examples/data/geojson/countries.geojson',
          format: new ol.format.GeoJSON()
        }),
        style: getStackedStyle
      });*/
      var getStackedStyle = function(feature, resolution) {
        var id = feature.getId();
        fill.setColor(id > 'J' ? gradient(feature, resolution) : pattern);
        return style;
      };
      var stroke = new ol.style.Stroke({color: 'black', width: 2});
      var fill = new ol.style.Fill(pattern);
      var fill2 = new ol.style.Fill();
     /* fill2..setColor(patter);*/
      var style2 = new ol.style.Style({
            stroke: new ol.style.Stroke({
           color: '#333',
           width: 2
        })
      });
      fill.setColor(pattern);
      var styles = {
        'custom': style2,
        'square': new ol.style.Style({
          image: new ol.style.RegularShape({
            fill: fill,
            stroke: stroke,
            points: 4,
            radius: 10,
            angle: Math.PI / 4
          })
        }),
        'triangle': new ol.style.Style({
          image: new ol.style.RegularShape({
            fill: fill,
            stroke: stroke,
            points: 3,
            radius: 10,
            rotation: Math.PI / 4,
            angle: 0
          })
        }),
        'star': new ol.style.Style({
          image: new ol.style.RegularShape({
            fill: fill,
            stroke: stroke,
            points: 5,
            radius: 10,
            radius2: 4,
            angle: 0
          })
        }),
        'cross': new ol.style.Style({
          image: new ol.style.RegularShape({
            fill: fill,
            stroke: stroke,
            points: 4,
            radius: 10,
            radius2: 0,
            angle: 0
          })
        }),
        'x': new ol.style.Style({
          image: new ol.style.RegularShape({
            fill: fill,
            stroke: stroke,
            points: 4,
            radius: 10,
            radius2: 0,
            angle: Math.PI / 4
          })
        })
      };


      var styleKeys = ['x', 'cross', 'star', 'triangle', 'square'];
      var count = 250;
      var features = new Array(count);
      var e = 4500000;
      for (var i = 0; i < count; ++i) {
        var coordinates = [2 * e * Math.random() - e, 2 * e * Math.random() - e];
        features[i] = new ol.Feature(new ol.geom.Point(coordinates));
        features[i].setStyle(styles[styleKeys[Math.floor(Math.random() * 5)]]);
      }

      var source = new ol.source.Vector({
        features: features
      });

     /* */var vectorLayer = new ol.layer.Vector({
        source: source,
        style: getStackedStyle
      });

      // Create a vector layer that makes use of the style function above…
      var vectorLayer2 = new ol.layer.Vector({
        source: new ol.source.Vector({
          url: 'https://openlayers.org/en/v4.2.0/examples/data/geojson/countries.geojson',
          format: new ol.format.GeoJSON()
        }),
      
      });/**/
      var map = new ol.Map({
        layers: [
          vectorLayer, vectorLayer2
        ],
        target: 'map',
        view: new ol.View({
          center: [0, 0],
          zoom: 2
        })
      });
    </script>
  </body>
</html>

Thanks, will try it this evening and your suggestion with two strokes — Cabe Skuriles, Jul 10 '17 at 06:01

Openlayers 4 use canvas pattern for feature style

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