mapnik2_erase_patch.diff

Index: src/cairo_renderer.cpp
===================================================================
--- src/cairo_renderer.cpp	(revision 2643)
+++ src/cairo_renderer.cpp	(working copy)
@@ -307,7 +307,7 @@
     {
         context_->set_line_width(width);
     }
-
+    
     void set_dash(dash_array const &dashes)
     {
         std::valarray<double> d(dashes.size() * 2);
@@ -329,6 +329,11 @@
         context_->set_fill_rule(fill_rule);
     }
 
+    void set_operator(Cairo::Operator op)
+    {
+        context_->set_operator(op);
+    }
+
     void move_to(double x, double y)
     {
 #if CAIRO_VERSION < CAIRO_VERSION_ENCODE(1, 6, 0)
@@ -609,9 +614,15 @@
 
         set_line_width(halo_radius);
         set_line_join(ROUND_JOIN);
-        set_color(halo_fill);
-        stroke();
-
+        if (halo_fill.rgba() == 0)
+        {
+            set_operator(Cairo::OPERATOR_DEST_OUT);
+            stroke();
+            set_operator(Cairo::OPERATOR_OVER);
+        } else {
+            set_color(halo_fill);
+            stroke();
+        }
         set_color(fill);
 
         path.rewind();
@@ -746,7 +757,12 @@
 
     cairo_context context(context_);
 
-    context.set_color(sym.get_fill(), sym.get_opacity());
+    if (sym.get_fill().rgba() == 0) {
+        context.set_color(0, 0, 0, 1.0);
+        context.set_operator(Cairo::OPERATOR_DEST_OUT);
+    } else {
+        context.set_color(sym.get_fill(), sym.get_opacity());
+    }
 
     for (unsigned i = 0; i < feature.num_geometries(); ++i)
     {
@@ -760,6 +776,8 @@
             context.fill();
         }
     }
+    
+    context.set_operator(Cairo::OPERATOR_OVER);
 }
 
 typedef boost::tuple<double,double,double,double> segment_t;