stub in new alpha manipulation functions for mapnik image - #609

bindings/python/mapnik_image.cpp

@@ -185,6 +185,9 @@ void export_image()
         .add_property("background",make_function
                       (&image_32::get_background,return_value_policy<copy_const_reference>()),
                       &image_32::set_background, "The background color of the image.")
+        .def("set_grayscale_to_alpha",&image_32::set_grayscale_to_alpha, "Set the grayscale values to the alpha channel of the Image")
+        .def("set_color_to_alpha",&image_32::set_color_to_alpha, "Set a given color to the alpha channel of the Image")
+        .def("set_alpha",&image_32::set_alpha, "Set the overall alpha channel of the Image")
         .def("blend",&blend)
         .def("composite",&composite)
         .def("tostring",&tostring1)

include/mapnik/graphics.hpp

@@ -149,10 +149,22 @@ public:
     image_32(Cairo::RefPtr<Cairo::ImageSurface> rhs);
 #endif
     ~image_32();
+    
     void set_background(color const& background);
-    const color& get_background() const;
-    const image_data_32& data() const;
 
+    const color& get_background() const;
+
+    void set_grayscale_to_alpha();
+
+    void set_color_to_alpha(color const& c);
+
+    void set_alpha(float opacity);
+    
+    inline const image_data_32& data() const
+    {
+        return data_;
+    }
+    
     inline image_data_32& data()
     {
         return data_;

src/graphics.cpp

@@ -24,6 +24,7 @@
 // mapnik
 #include <mapnik/graphics.hpp>
 #include <mapnik/image_util.hpp>
+#include <mapnik/global.hpp>
 
 // cairo
 #ifdef HAVE_CAIRO
@@ -90,9 +91,19 @@ image_32::image_32(Cairo::RefPtr<Cairo::ImageSurface> rhs)
 
 image_32::~image_32() {}
 
-const image_data_32& image_32::data() const
+void image_32::set_grayscale_to_alpha()
 {
-    return data_;
+
+}
+
+void image_32::set_color_to_alpha(const color& c)
+{
+
+}
+
+void image_32::set_alpha(float opacity)
+{
+
 }
 
 void image_32::set_background(const color& background)