add mapnik.Image.premultiplied() to query status of pixel premultiplication

CHANGELOG.md

@@ -6,6 +6,10 @@ Developers: Please commit along with changes.
 
 For a complete change history, see the git log.
 
+## Future
+
+- Added `premultiplied` property on mapnik::image_32 / mapnik.Image to enable knowledge of premultiplied status of image buffer.
+
 ## 2.2.0
 
 Released June 3rd, 2013

bindings/python/mapnik_image.cpp

@@ -272,6 +272,7 @@ void export_image()
            arg("mode")=mapnik::src_over,
            arg("opacity")=1.0f
          ))
+        .def("premultiplied",&image_32::premultiplied)
         .def("premultiply",&image_32::premultiply)
         .def("demultiply",&image_32::demultiply)
         .def("set_pixel",&set_pixel)

include/mapnik/graphics.hpp

@@ -54,6 +54,7 @@ private:
     boost::optional<color> background_;
     image_data_32 data_;
     bool painted_;
+    bool premultiplied_;
 public:
     image_32(int width,int height);
     image_32(image_32 const& rhs);
@@ -72,6 +73,11 @@ public:
         return painted_;
     }
 
+    bool premultiplied() const
+    {
+        return premultiplied_;
+    }
+
     inline void clear()
     {
         std::memset(data_.getData(),0,sizeof(mapnik::image_data_32::pixel_type)*data_.width()*data_.height());

src/graphics.cpp

@@ -45,19 +45,22 @@ image_32::image_32(int width,int height)
     :width_(width),
      height_(height),
      data_(width,height),
-     painted_(false) {}
+     painted_(false),
+     premultiplied_(false) {}
 
 image_32::image_32(const image_32& rhs)
     :width_(rhs.width_),
      height_(rhs.height_),
      data_(rhs.data_),
-     painted_(rhs.painted_)  {}
+     painted_(rhs.painted_),
+     premultiplied_(rhs.premultiplied_) {}
 
 #ifdef HAVE_CAIRO
 image_32::image_32(cairo_surface_ptr const& surface)
     :width_(cairo_image_surface_get_width(&*surface)),
      height_(cairo_image_surface_get_height(&*surface)),
-     data_(width_, height_)
+     data_(width_, height_),
+     premultiplied_(false)
 {
     painted_ = true;
     if ( cairo_image_surface_get_format(&*surface) != CAIRO_FORMAT_ARGB32)
@@ -193,6 +196,7 @@ void image_32::premultiply()
     agg::rendering_buffer buffer(data_.getBytes(),width_,height_,width_ * 4);
     agg::pixfmt_rgba32 pixf(buffer);
     pixf.premultiply();
+    premultiplied_ = true;
 }
 
 void image_32::demultiply()
@@ -200,6 +204,7 @@ void image_32::demultiply()
     agg::rendering_buffer buffer(data_.getBytes(),width_,height_,width_ * 4);
     agg::pixfmt_rgba32 pixf(buffer);
     pixf.demultiply();
+    premultiplied_ = false;
 }
 
 void image_32::composite_pixel(unsigned op, int x,int y, unsigned c, unsigned cover, double opacity)

tests/python_tests/image_test.py

@@ -12,6 +12,14 @@ def setup():
     # from another directory we need to chdir()
     os.chdir(execution_path('.'))
 
+def test_image_premultiply():
+    im = mapnik.Image(256,256)
+    eq_(im.premultiplied(),False)
+    im.premultiply()
+    eq_(im.premultiplied(),True)
+    im.demultiply()
+    eq_(im.premultiplied(),False)
+
 @raises(RuntimeError)
 def test_negative_image_dimensions():
     im = mapnik.Image(-40,40)