Add filter function to translate interaction

Add a filter function to the translate interaction. This filter is similar to the one present in the select interaction options and provides the ability to dynamically filter which features to include in the translate interaction. Adding the existing "features" options allows further filtering to take place. In this case the filter is first applied, and features that are passing the filtering need to be present in the "features" options to be further kept. The default filter function always return true (no filtering).

src/ol/interaction/Translate.js

@@ -45,6 +45,10 @@ const TranslateEventType = {
  * function will be called for each layer in the map and should return
  * `true` for layers that you want to be translatable. If the option is
  * absent, all visible layers will be considered translatable.
+ * @property {FilterFunction} [filter] A function
+ * that takes an {@link module:ol/Feature} and an
+ * {@link module:ol/layer/Layer} and returns `true` if the feature may be
+ * translated or `false` otherwise.
  * @property {number} [hitTolerance=0] Hit-detection tolerance. Pixels inside the radius around the given position
  * will be checked for features.
  */
@@ -136,6 +140,12 @@ class Translate extends PointerInteraction {
      */
     this.layerFilter_ = layerFilter;
 
+    /**
+     * @private
+     * @type {FilterFunction}
+     */
+    this.filter_ = options.filter ? options.filter : TRUE;
+
     /**
      * @private
      * @type {number}
@@ -245,9 +255,11 @@ class Translate extends PointerInteraction {
    */
   featuresAtPixel_(pixel, map) {
     return map.forEachFeatureAtPixel(pixel,
-      function(feature) {
-        if (!this.features_ || includes(this.features_.getArray(), feature)) {
-          return feature;
+      function(feature, layer) {
+        if (this.filter_(feature, layer)) {
+          if (!this.features_ || includes(this.features_.getArray(), feature)) {
+            return feature;
+          }
         }
       }.bind(this), {
         layerFilter: this.layerFilter_,