renderers can now report to image if any features have been rendered via im.painted(), and im.background now uses boost optional to allow easy detection of whether a background has been set - closes #875

include/mapnik/agg_renderer.hpp

@@ -109,6 +109,10 @@ public:
         // agg renderer doesn't support processing of multiple symbolizers.
         return false;
     };
+    void painted(bool painted)
+    {
+        pixmap_.painted(painted);
+    }
 
 private:
     T & pixmap_;

include/mapnik/cairo_renderer.hpp

@@ -125,6 +125,11 @@ public:
         // cairo renderer doesn't support processing of multiple symbolizers.
         return false;
     };
+    void painted(bool /*painted*/)
+    {
+        // nothing to do
+    }
+
 protected:
     void render_marker(const int x, const int y, marker &marker, const agg::trans_affine & mtx, double opacity=1.0);
 

include/mapnik/graphics.hpp

@@ -24,6 +24,7 @@
 
 #ifndef GRAPHICS_HPP
 #define GRAPHICS_HPP
+
 // mapnik
 #include <mapnik/color.hpp>
 #include <mapnik/gamma.hpp>
@@ -42,6 +43,9 @@
 #include <cairomm/surface.h>
 #endif
 
+// boost
+#include <boost/optional/optional.hpp>
+
 namespace mapnik
 {
 
@@ -140,8 +144,9 @@ class MAPNIK_DECL image_32
 private:
     unsigned width_;
     unsigned height_;
-    color background_;
+    boost::optional<color> background_;
     image_data_32 data_;
+    bool painted_;
 public:
     image_32(int width,int height);
     image_32(image_32 const& rhs);
@@ -150,9 +155,19 @@ public:
 #endif
     ~image_32();
 
-    void set_background(color const& background);
+    void painted(bool painted)
+    {
+        painted_ = painted;
+    }
 
-    const color& get_background() const;
+    bool painted() const
+    {
+        return painted_;
+    }
+
+    boost::optional<color> const& get_background() const;
+    
+    void set_background(const color& c);
 
     void set_grayscale_to_alpha();
 

include/mapnik/grid/grid.hpp

@@ -65,6 +65,7 @@ private:
     data_type data_;
     std::set<std::string> names_;
     unsigned int resolution_;
+    bool painted_;
     
 public:
 
@@ -94,6 +95,16 @@ public:
     
     ~hit_grid() {}
 
+    void painted(bool painted)
+    {
+        painted_ = painted;
+    }
+
+    bool painted() const
+    {
+        return painted_;
+    }
+
     void add_feature(mapnik::Feature const& feature)
     {
 

include/mapnik/grid/grid_renderer.hpp

@@ -108,6 +108,10 @@ public:
         // grid renderer doesn't support processing of multiple symbolizers.
         return false;
     };
+    void painted(bool painted)
+    {
+        pixmap_.painted(painted);
+    }
 
 private:
     T & pixmap_;

src/feature_style_processor.cpp

@@ -424,6 +424,8 @@ void feature_style_processor<Processor>::apply_to_layer(layer const& lay, Proces
                         feat_processed = true;
                         #endif
                         
+                        p.painted(true);
+
                         do_else=false;
                         do_also=true;
                         rule::symbolizers const& symbols = r->get_symbolizers();
@@ -455,6 +457,8 @@ void feature_style_processor<Processor>::apply_to_layer(layer const& lay, Proces
                         feat_processed = true;
                         #endif
 
+                        p.painted(true);
+ 
                         rule::symbolizers const& symbols = r->get_symbolizers();
                         // if the underlying renderer is not able to process the complete set of symbolizers,
                         // process one by one.
@@ -477,6 +481,8 @@ void feature_style_processor<Processor>::apply_to_layer(layer const& lay, Proces
                         feat_processed = true;
                         #endif
 
+                        p.painted(true);
+ 
                         rule::symbolizers const& symbols = r->get_symbolizers();
                         // if the underlying renderer is not able to process the complete set of symbolizers,
                         // process one by one.

src/graphics.cpp

@@ -40,12 +40,14 @@ namespace mapnik
 image_32::image_32(int width,int height)
     :width_(width),
      height_(height),
-     data_(width,height) {}
+     data_(width,height),
+     painted_(false) {}
 
 image_32::image_32(const image_32& rhs)
     :width_(rhs.width_),
      height_(rhs.height_),
-     data_(rhs.data_)  {}
+     data_(rhs.data_),
+     painted_(rhs.painted_)  {}
 
 #ifdef HAVE_CAIRO
 image_32::image_32(Cairo::RefPtr<Cairo::ImageSurface> rhs)
@@ -53,6 +55,7 @@ image_32::image_32(Cairo::RefPtr<Cairo::ImageSurface> rhs)
      height_(rhs->get_height()),
      data_(rhs->get_width(),rhs->get_height())
 {
+    painted_ = true;
     if (rhs->get_format() != Cairo::FORMAT_ARGB32)
     {
         std::cerr << "Unable to convert this Cairo format\n";
@@ -159,14 +162,15 @@ void image_32::set_alpha(float opacity)
 
 }
 
-void image_32::set_background(const color& background)
+void image_32::set_background(const color& c)
 {
-    background_=background;
-    data_.set(background_.rgba());
+    background_=c;
+    data_.set(background_->rgba());
 }
 
-const color& image_32::get_background() const
+boost::optional<color> const& image_32::get_background() const
 {
     return background_;
 }
+
 }