2 files changed, 34 insertions, 46 deletions

diff --git a/libdimensionxx/dimensionxx/canvas.hpp b/libdimensionxx/dimensionxx/canvas.hpp
index f519fbd..b8f2887 100644
--- a/libdimensionxx/dimensionxx/canvas.hpp
+++ b/libdimensionxx/dimensionxx/canvas.hpp
@@ -23,6 +23,8 @@
 #ifndef DIMENSIONXX_CANVAS_HPP
 #define DIMENSIONXX_CANVAS_HPP
 
+#include <tr1/memory>
+
 namespace Dimension
 {
   // Base canvas class.  Wraps a dmnsn_canvas*.
@@ -31,10 +33,14 @@ namespace Dimension
   public:
     // Allocate a dmnsn_canvas of specified width and height
     Canvas(unsigned int width, unsigned int height);
+
     // Wrap an existing canvas
     explicit Canvas(dmnsn_canvas* canvas);
+
+    // Canvas(const Canvas& canvas);
+
     // Delete the canvas
-    virtual ~Canvas();
+    ~Canvas();
 
     // Get the width and height
     unsigned int width() const;
@@ -48,17 +54,11 @@ namespace Dimension
     dmnsn_canvas*       dmnsn();
     const dmnsn_canvas* dmnsn() const;
 
-  protected:
-    // Derived classes may want to set m_canvas later.  Set it to NULL now, so
-    // that the destructor can still dmnsn_delete_canvas it.
-    Canvas();
-
-    dmnsn_canvas* m_canvas;
-
   private:
-    // Copying prohibited
-    Canvas(const Canvas&);
+    // Copy-assignment prohibited
     Canvas& operator=(const Canvas&);
+
+    std::tr1::shared_ptr<dmnsn_canvas*> m_canvas;
   };
 }
 
diff --git a/libdimensionxx/dimensionxx/png.hpp b/libdimensionxx/dimensionxx/png.hpp
index 980840c..17cb883 100644
--- a/libdimensionxx/dimensionxx/png.hpp
+++ b/libdimensionxx/dimensionxx/png.hpp
@@ -28,55 +28,43 @@
 
 namespace Dimension
 {
-  // PNG_Canvas handles reading a Canvas from a PNG file, writing one to a PNG
-  // file, or both, depending on what type of stream(s) are given to the
-  // constructor.
-  class PNG_Canvas : public Canvas
+  class PNG_Writer
   {
   public:
-    // Input PNG_Canvas; read the Canvas from istr now
-    explicit PNG_Canvas(std::istream& istr);
+    PNG_Writer(Canvas& canvas, std::ostream& ostr);
+    ~PNG_Writer();
 
-    // Output PNG_Canvas; write the Canvas to ostr at destruction, or when
-    // write() is called.
-    PNG_Canvas(unsigned int x, unsigned int y, std::ostream& ostr);
-
-    // I/O PNG_Canvas; read the Canvas from istr now, and write to ostr at
-    // destruction or then write() is called.
-    PNG_Canvas(std::istream& istr, std::ostream& ostr);
+    void write();
+    Progress write_async();
 
-    // Call write() if we're an output PNG_Canvas, but trap any exceptions and
-    // report a dmnsn_error() instead.
-    virtual ~PNG_Canvas();
+  private:
+    // Copying prohibited
+    PNG_Writer(const PNG_Writer&);
+    PNG_Writer& operator=(const PNG_Writer&);
 
-    // Write the Canvas to the output stream, throwing a Dimension_Error on
-    // error.
-    void write();
+    Canvas* m_canvas;
+    std::ostream* m_ostr;
+    bool m_written;
+  };
 
-    // Write the Canvas to the output stream in the background
-    Progress write_async();
+  class PNG_Reader
+  {
+  public:
+    PNG_Reader(std::istream& istr);
+    // ~PNG_Reader();
 
-    // Construct an input or I/O PNG_Canvas in the background
-    static Progress read_async(std::istream& istr);
-    explicit PNG_Canvas(Progress& progress);
-    explicit PNG_Canvas(Progress& progress, std::ostream& ostr);
+    Canvas read();
 
-  protected:
-    // In case a derived class needs to set m_canvas after we're constructed
-    explicit PNG_Canvas(std::ostream& ostr);
+    Progress read_async();
+    static Canvas finish(Progress& progress);
 
   private:
     // Copying prohibited
-    PNG_Canvas(const PNG_Canvas&);
-    PNG_Canvas& operator=(const PNG_Canvas&);
+    PNG_Reader(const PNG_Reader&);
+    PNG_Reader& operator=(const PNG_Reader&);
 
     std::istream* m_istr;
-    std::ostream* m_ostr;
-    bool m_written;
-
-    // Read the Canvas from a PNG file, and throw a Dimension_Error upon
-    // failure.
-    void read();
+    bool m_read;
   };
 }