add image/grid clear methods to make it easier to quickly re-use previously allocated objects for rendering - closes #1571

bindings/python/mapnik_grid.cpp

@@ -66,6 +66,7 @@ void export_grid()
         .def("height",&mapnik::grid::height)
         .def("view",&mapnik::grid::get_view)
         .def("get_pixel",&get_pixel)
+        .def("clear",&mapnik::grid::clear)
         .def("encode",encode,
              ( boost::python::arg("encoding")="utf", boost::python::arg("features")=true,boost::python::arg("resolution")=4 ),
              "Encode the grid as as optimized json\n"

bindings/python/mapnik_image.cpp

@@ -235,6 +235,7 @@ void export_image()
         .def("demultiply",&image_32::demultiply)
         .def("set_pixel",&set_pixel)
         .def("get_pixel",&get_pixel)
+        .def("clear",&image_32::clear)
         //TODO(haoyu) The method name 'tostring' might be confusing since they actually return bytes in Python 3
 
         .def("tostring",&tostring1)

include/mapnik/graphics.hpp

@@ -72,6 +72,11 @@ public:
         return painted_;
     }
 
+    inline void clear()
+    {
+        std::memset(data_.getData(),0,sizeof(mapnik::image_data_32::pixel_type)*data_.width()*data_.height());
+    }
+
     boost::optional<color> const& get_background() const;
 
     void set_background(const color& c);

include/mapnik/grid/grid.hpp

@@ -82,6 +82,8 @@ public:
 
     ~hit_grid() {}
 
+    void clear();
+
     inline void painted(bool painted)
     {
         painted_ = painted;

src/grid/grid.cpp

@@ -65,6 +65,18 @@ hit_grid<T>::hit_grid(hit_grid<T> const& rhs)
           data_.set(base_mask);
       }
 
+template <typename T>
+void hit_grid<T>::clear()
+{
+    painted_ = false;
+    f_keys_.clear();
+    features_.clear();
+    names_.clear();
+    f_keys_[base_mask] = "";
+    data_.set(base_mask);
+    ctx_ = boost::make_shared<mapnik::context_type>();
+}
+
 template <typename T>
 void hit_grid<T>::add_feature(mapnik::feature_impl & feature)
 {

tests/python_tests/buffer_clear_test.py

@@ -0,0 +1,63 @@
+import sys
+import os, mapnik
+from timeit import Timer, time
+from nose.tools import *
+from utilities import execution_path
+
+def setup():
+    # All of the paths used are relative, if we run the tests
+    # from another directory we need to chdir()
+    os.chdir(execution_path('.'))
+
+def test_clearing_image_data():
+    im = mapnik.Image(256,256)
+    # make sure it equals itself
+    bytes = im.tostring()
+    eq_(im.tostring(),bytes)
+    # set background, then clear
+    im.background = mapnik.Color('green')
+    eq_(im.tostring()!=bytes,True)
+    # clear image, should now equal original
+    im.clear()
+    eq_(im.tostring(),bytes)
+
+def make_map():
+    ds = mapnik.MemoryDatasource()
+    context = mapnik.Context()
+    context.push('Name')
+    pixel_key = 1
+    f = mapnik.Feature(context,pixel_key)
+    f['Name'] = str(pixel_key)
+    f.add_geometries_from_wkt('POLYGON ((0 0, 0 256, 256 256, 256 0, 0 0))')
+    ds.add_feature(f)
+    s = mapnik.Style()
+    r = mapnik.Rule()
+    symb = mapnik.PolygonSymbolizer()
+    r.symbols.append(symb)
+    s.rules.append(r)
+    lyr = mapnik.Layer('Places')
+    lyr.datasource = ds
+    lyr.styles.append('places_labels')
+    width,height = 256,256
+    m = mapnik.Map(width,height)
+    m.append_style('places_labels',s)
+    m.layers.append(lyr)
+    m.zoom_all()
+    return m
+
+def test_clearing_grid_data():
+    g = mapnik.Grid(256,256)
+    utf = g.encode()
+    # make sure it equals itself
+    eq_(g.encode(),utf)
+    m = make_map()
+    mapnik.render_layer(m,g,layer=0,fields=['__id__','Name'])
+    eq_(g.encode()!=utf,True)
+    # clear grid, should now match original
+    g.clear()
+    eq_(g.encode(),utf)
+
+
+if __name__ == "__main__":
+    setup()
+    [eval(run)() for run in dir() if 'test_' in run]