Giving vector layers the style they deserve

Now vector layers can have a style. ol.Style instances have an
apply method to get the symbolizer literals for a feature. If the
layer does not have a style defined, there is also a static
applyDefaultStyle function on ol.Style to get the default
symbolizer literals for a feature. The vector layer also got a
groupFeaturesBySymbolizerLiteral method, which returns an array
with features grouped by symbolizer, as needed by the canvas
renderer.

src/ol/layer/vectorlayer.js

@@ -1,7 +1,9 @@
 goog.provide('ol.layer.Vector');
 
+goog.require('ol.Feature');
 goog.require('ol.layer.Layer');
 goog.require('ol.source.Vector');
+goog.require('ol.style.Style');
 
 
 
@@ -12,6 +14,13 @@ goog.require('ol.source.Vector');
  */
 ol.layer.Vector = function(layerOptions) {
   goog.base(this, layerOptions);
+
+  /**
+   * @private
+   * @type {ol.style.Style}
+   */
+  this.style_ = goog.isDef(layerOptions.style) ? layerOptions.style : null;
+
 };
 goog.inherits(ol.layer.Vector, ol.layer.Layer);
 
@@ -22,3 +31,38 @@ goog.inherits(ol.layer.Vector, ol.layer.Layer);
 ol.layer.Vector.prototype.getVectorSource = function() {
   return /** @type {ol.source.Vector} */ (this.getSource());
 };
+
+
+/**
+ * @param {Array.<ol.Feature>} features Features.
+ * @return {Array.<Array>} symbolizers for features.
+ */
+ol.layer.Vector.prototype.groupFeaturesBySymbolizerLiteral =
+    function(features) {
+  var uniqueLiterals = {},
+      featuresBySymbolizer = [],
+      style = this.style_,
+      feature, literals, literal, key;
+  for (var i = 0, ii = features.length; i < ii; ++i) {
+    feature = features[i];
+    literals = goog.isNull(style) ?
+        ol.style.Style.applyDefaultStyle(feature) :
+        style.apply(feature);
+    for (var j = 0, jj = literals.length; j < jj; ++j) {
+      literal = literals[j];
+      for (var l in uniqueLiterals) {
+        if (literal.equals(uniqueLiterals[l])) {
+          literal = uniqueLiterals[l];
+          break;
+        }
+      }
+      key = goog.getUid(literal);
+      if (!goog.object.containsKey(uniqueLiterals, key)) {
+        uniqueLiterals[key] = featuresBySymbolizer.length;
+        featuresBySymbolizer.push([[], literal]);
+      }
+      featuresBySymbolizer[uniqueLiterals[key]][0].push(feature);
+    }
+  }
+  return featuresBySymbolizer;
+};