use featureset_buffer for simplier render time feature cache from @Mappy

include/mapnik/feature_style_processor_impl.hpp

@@ -45,6 +45,7 @@
 #include <mapnik/scale_denominator.hpp>
 #include <mapnik/projection.hpp>
 #include <mapnik/proj_transform.hpp>
+#include <mapnik/util/featureset_buffer.hpp>
 
 // boost
 #include <boost/variant/apply_visitor.hpp>
@@ -255,7 +256,8 @@ void feature_style_processor<Processor>::apply_to_layer(layer const& lay, Proces
 
     // clip buffered extent by maximum extent, if supplied
     boost::optional<box2d<double> > const& maximum_extent = m_.maximum_extent();
-    if (maximum_extent) {
+    if (maximum_extent)
+    {
         buffered_query_ext.clip(*maximum_extent);
     }
 
@@ -431,24 +433,22 @@ void feature_style_processor<Processor>::apply_to_layer(layer const& lay, Proces
         }
 
         // Also query the group by attribute
-        std::string group_by = lay.group_by();
-        if (group_by != "")
+        std::string const& group_by = lay.group_by();
+        if (!group_by.empty())
         {
             q.add_property_name(group_by);
         }
 
         bool cache_features = lay.cache_features() && active_styles.size() > 1;
 
-        // Render incrementally when the column that we group by
-        // changes value.
-        if (group_by != "")
+        // Render incrementally when the column that we group by changes value.
+        if (!group_by.empty())
         {
             featureset_ptr features = ds->features(q);
-            if (features) {
-                // Cache all features into the memory_datasource before rendering.
-                memory_datasource cache(ds->type(),false);
+            if (features)
+            {
+                boost::shared_ptr<featureset_buffer> cache = boost::make_shared<featureset_buffer>();
                 feature_ptr feature, prev;
-
                 while ((feature = features->next()))
                 {
                     if (prev && prev->get(group_by) != feature->get(group_by))
@@ -458,44 +458,49 @@ void feature_style_processor<Processor>::apply_to_layer(layer const& lay, Proces
                         int i = 0;
                         BOOST_FOREACH (feature_type_style const* style, active_styles)
                         {
+                            cache->prepare();
                             render_style(p, style, rule_caches[i], style_names[i],
-                                         cache.features(q), prj_trans);
+                                         cache, prj_trans);
                             i++;
                         }
-                        cache.clear();
+                        cache->clear();
                     }
-                    cache.push(feature);
+                    cache->push(feature);
                     prev = feature;
                 }
 
                 int i = 0;
                 BOOST_FOREACH (feature_type_style const* style, active_styles)
                 {
+                    cache->prepare();
                     render_style(p, style, rule_caches[i], style_names[i],
-                                 cache.features(q), prj_trans);
+                                 cache, prj_trans);
                     i++;
                 }
             }
         }
         else if (cache_features)
         {
-            memory_datasource cache(ds->type(),false);
             featureset_ptr features = ds->features(q);
-            if (features) {
+            boost::shared_ptr<featureset_buffer> cache = boost::make_shared<featureset_buffer>();
+            if (features)
+            {
                 // Cache all features into the memory_datasource before rendering.
                 feature_ptr feature;
                 while ((feature = features->next()))
                 {
-                    cache.push(feature);
+                    cache->push(feature);
                 }
             }
             int i = 0;
             BOOST_FOREACH (feature_type_style const* style, active_styles)
             {
+                cache->prepare();
                 render_style(p, style, rule_caches[i], style_names[i],
-                             cache.features(q), prj_trans);
+                             cache, prj_trans);
                 i++;
             }
+            cache->clear();
         }
         // We only have a single style and no grouping.
         else

include/mapnik/util/featureset_buffer.hpp

@@ -0,0 +1,77 @@
+/*****************************************************************************
+ *
+ * This file is part of Mapnik (c++ mapping toolkit)
+ *
+ * Copyright (C) 2013 Artem Pavlenko
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ *****************************************************************************/
+
+#ifndef MAPNIK_FEATURESET_BUFFER_HPP
+#define MAPNIK_FEATURESET_BUFFER_HPP
+
+// mapnik
+#include <mapnik/datasource.hpp>
+
+#include <vector>
+
+namespace mapnik {
+
+class featureset_buffer : public Featureset
+{
+public:
+    featureset_buffer()
+      : features_(),
+        pos_(),
+        end_()
+    {}
+
+    virtual ~featureset_buffer() {}
+
+    feature_ptr next()
+    {
+        if (pos_ != end_)
+        {
+            return *pos_++;
+        }
+        return feature_ptr();
+    }
+
+    void push(feature_ptr const& feature)
+    {
+        features_.push_back(feature);
+    }
+
+    void prepare()
+    {
+        pos_ = features_.begin();
+        end_ = features_.end();
+    }
+
+    void clear()
+    {
+        features_.clear();
+    }
+
+private:
+    std::vector<feature_ptr> features_;
+    std::vector<feature_ptr>::iterator pos_;
+    std::vector<feature_ptr>::iterator end_;
+};
+
+}
+
+#endif // MAPNIK_FEATURESET_BUFFER_HPP