[OpenLayers-Dev] Random Colors on Vector Features?

[Cameron Shorter]

If your desire is to get Openlayers to automatically set feature colors 
for you, I suggest using web safe colors. There are 256 of them, and 
they are all suitably different from each other, and it is easy to build 
an algorithm to create the colors.

Tim Schaub wrote:
> Picking up an old thread...
>
> Tim Schaub wrote:
>   
>> Hey-
>>
>> Christopher Schmidt wrote:
>>     
>>> I have a set of vector features. Each time I create a new feature, I
>>> want that feature to be styled such that it has a random color, chosen
>>> from a list of colors supplied by me.
>>> I see a couple of examples for 'unique style value' stuff, but that
>>> requires some unique attribute on my feature; I want to serialize the
>>> features later, so I don't want bogus attributes attached to them.
>>>
>>> Can I set a Style() object directly on the feature with my fillColor
>>> specified? Do I have to do something else? 
>>>       
>>     var colors = ["red", "orange", "yellow", "green", "blue", "purple"];
>>     var features = new Array(20);
>>     var x, y, fill;
>>     for(var i=0; i<20; i++) {
>>         x = Math.random() * 360 - 180;
>>         y = Math.random() * 180 - 90;
>>         fill = colors[Math.round((colors.length - 1) * Math.random())];
>>         features[i] = new OpenLayers.Feature.Vector(
>>             new OpenLayers.Geometry.Point(x, y), null,
>>             {fillColor: fill, pointRadius: 5}
>>         );
>>     }
>>
>> Setting a symbolizer directly on a feature still works.
>>
>>     
>
> But even less necessary if the patch #1434 gets in.
>
> Say you have 20 features with no "style":
>
>      var x, y;
>      var features = new Array(20);
>      for(var i=0; i<features.length; i++) {
>          x = Math.random() * 360 - 180;
>          y = Math.random() * 180 - 90;
>          features[i] = new OpenLayers.Feature.Vector(
>              new OpenLayers.Geometry.Point(x, y)
>          );
>      }
>      layer.addFeatures(features);
>      var colors = ["red", "green", "blue"];
>      layer.styleMap = new OpenLayers.StyleMap(new OpenLayers.Style(
>          {
>              pointRadius: 5,
>              fillColor: ${getColor}
>          }, {
>              getColor: function(feature) {
>                  return colors[parseInt(3 * Math.random())];
>              }
>          }
>      ));
>
> You can create a style map with a symbolizer template that runs whatever 
> function you want for each feature.  More verbose than giving each 
> feature a simple symbolizer, but way more useful (if you accept that 
> randomly styled features are less useful than features styled based on 
> something non-random).
>
> If you want to have features symbolized based on anything about the 
> feature (geometry area/length, fid, location, even intersection with 
> other features) you should do this with a style map.  Then, when you add 
> new features to your layer, when those features are drawn, the same 
> (underlying) rules get evaluated and symbolizers get created for those 
> features.  This makes the preFeatureInsert styling completely obsolete.
>
> As an added benefit, when you update something about your features that 
> is responsible for the feature styling, the symbolizer gets updated on 
> the next draw.  Move a feature whose style is based on position, the 
> style changes.  You don't get this with feature.style.
>
> Tim
>
>   
>> In the future, I think it would be good to encourage the use of 
>> FeatureId rules.  This could be facilitated by having layer.addFeature 
>> (to be written) optionally take a symbolizer.  If you specify a 
>> symbolizer when adding a feature to the layer, the layer would create a 
>> FeatureId rule for the corresponding feature (and add that rule to its 
>> styleMap).
>>
>> It might also make sense to have destroyFeatures remove the FeatureId 
>> rules for the given features from its styleMap.
>>
>> I'm curious about your use case.  I don't have a good idea how common it 
>> is to want to style a feature in a way that has nothing to do with its 
>> attributes.
>>
>> Tim
>>
>>     
>>> Regards,
>>>       
>>     
>
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>
>   


-- 
Cameron Shorter
Geospatial Systems Architect
Tel: +61 (0)2 8570 5050
Mob: +61 (0)419 142 254

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