Add some comments.

11 files changed, 190 insertions, 25 deletions

diff --git a/libdimensionxx/canvas.cpp b/libdimensionxx/canvas.cpp
index 2340066..411d4e8 100644
--- a/libdimensionxx/canvas.cpp
+++ b/libdimensionxx/canvas.cpp
@@ -22,8 +22,59 @@
 
 namespace Dimension
 {
+  // Allocate the canvas with dmnsn_new_canvas()
+  Canvas::Canvas(unsigned int width, unsigned int height)
+    : m_canvas(dmnsn_new_canvas(width, height)) { }
+
+  // Virtual destructor: delete the canvas with dmnsn_delete_canvas().
   Canvas::~Canvas()
   {
     dmnsn_delete_canvas(m_canvas);
   }
+
+  // Get the width
+  unsigned int
+  Canvas::width() const
+  {
+    return m_canvas->x;
+  }
+
+  // Get the height
+  unsigned int
+  Canvas::height() const
+  {
+    return m_canvas->y;
+  }
+
+  // Get a particular pixel, thread-safely, with dmnsn_get_pixel().
+  Color
+  Canvas::pixel(unsigned int x, unsigned int y) const
+  {
+    return Color(dmnsn_get_pixel(m_canvas, x, y));
+  }
+
+  // Set a particular pixel, thread-safely, with dmnsn_set_pixel().
+  void
+  Canvas::pixel(unsigned int x, unsigned int y, const Color& c)
+  {
+    dmnsn_set_pixel(m_canvas, x, y, c.dmnsn());
+  }
+
+  // Return the wrapped canvas
+  dmnsn_canvas* 
+  Canvas::dmnsn()
+  {
+    return m_canvas;
+  }
+
+  // Return a const version of the wrapped canvas
+  const dmnsn_canvas*
+  Canvas::dmnsn() const
+  {
+    return m_canvas;
+  }
+
+  // Protected default constructor: set m_canvas to NULL.
+  Canvas::Canvas()
+    : m_canvas(0) { }
 }
diff --git a/libdimensionxx/color.cpp b/libdimensionxx/color.cpp
index c7f768a..ffbc808 100644
--- a/libdimensionxx/color.cpp
+++ b/libdimensionxx/color.cpp
@@ -22,5 +22,6 @@
 
 namespace Dimension
 {
+  // Definition of whitepoint
   const CIE_XYZ whitepoint(dmnsn_whitepoint);
 }
diff --git a/libdimensionxx/cookie.cpp b/libdimensionxx/cookie.cpp
index dd8a06d..c3b1541 100644
--- a/libdimensionxx/cookie.cpp
+++ b/libdimensionxx/cookie.cpp
@@ -21,10 +21,20 @@
 #include "dimensionxx.hpp"
 #include <stdio.h>
 
+// The conundrum: libdimension and libdimension-* use C I/O, with FILE*'s.
+// We want to use C++ I/O with std::i/ostreams.  Unfortunately, there's no
+// standard way to map between them, so we use the nonportable GNU stdio
+// extension fopencookie(), which creates a FILE* with custom read/write/seek
+// functions.  BSD also has a similar function, funopen(), which we should
+// use too.  Failing in all that, we should fall back on a tmpfile() buffer,
+// but that would require an fclosecookie() function as well, to copy the
+// buffer to the stream potentially.
+
 namespace Dimension
 {
   namespace
   {
+    // Internal cookie type to hold the C++ streams.
     struct Cookie
     {
     public:
@@ -32,43 +42,50 @@ namespace Dimension
       std::ostream* ostr;
     };
 
+    // Cookie read function
     ssize_t
     cookie_read(void* cookie, char* buf, size_t size)
     {
       Cookie* streams = reinterpret_cast<Cookie*>(cookie);
 
+      // Do the unformatted read
       streams->istr->read(buf, size);
 
-      if (streams->istr->eof()) {
-        return streams->istr->gcount();
-      } else if (!streams->istr->good()) {
-        return -1;
+      if (streams->istr->eof() || streams->istr->good()) {
+        return streams->istr->gcount(); // This returns 0 on an immediate EOF
+                                        // for us.
       } else {
-        return streams->istr->gcount();
+        // Some non-EOF error
+        return -1;
       }
     }
 
+    // Cookie write function
     ssize_t
     cookie_write(void* cookie, const char* buf, size_t size)
     {
       Cookie* streams = reinterpret_cast<Cookie*>(cookie);
 
+      // Do the unformatted write
       streams->ostr->write(buf, size);
 
-      if (!streams->ostr->good()) {
-        return -1;
-      } else {
+      if (streams->ostr->good()) {
+        // Write operation succeeded, so we must've written size bytes
         return size;
+      } else {
+        // Write operation failed
+        return -1;
       }
     }
 
+    // Cookie seek function
     int
     cookie_seek(void* cookie, off64_t* offset, int whence)
     {
       Cookie* streams = reinterpret_cast<Cookie*>(cookie);
-      bool success = true;
 
       if (streams->istr) {
+        // If we have an input stream, seek it
         switch (whence) {
         case SEEK_SET:
           streams->istr->seekg(*offset, std::ios::beg);
@@ -82,11 +99,13 @@ namespace Dimension
         }
 
         if (!streams->istr->good()) {
-          success = false;
+          // Seek failed
+          return 1;
         }
       }
 
       if (streams->ostr) {
+        // If we have an output stream, seek it too
         switch (whence) {
         case SEEK_SET:
           streams->ostr->seekp(*offset, std::ios::beg);
@@ -99,20 +118,25 @@ namespace Dimension
         }
 
         if (!streams->ostr->good()) {
-          success = false;
+          // Seek failed
+          return 1;
         }
       }
 
-      return !success;
+      // Seek succeeded
+      return 0;
     }
 
+    // Cookie delete function
     int
     cookie_close(void* cookie)
     {
+      // Free the cookie
       delete reinterpret_cast<Cookie*>(cookie);
     }
   }
 
+  // Make an input FILE*
   std::FILE*
   fcookie(std::istream& istr)
   {
@@ -129,6 +153,7 @@ namespace Dimension
     return fopencookie(reinterpret_cast<void*>(cookie), "r", io_funcs);
   }
 
+  // Make an output FILE*
   std::FILE*
   fcookie(std::ostream& ostr)
   {
@@ -145,6 +170,7 @@ namespace Dimension
     return fopencookie(reinterpret_cast<void*>(cookie), "w", io_funcs);
   }
 
+  // Make an I/O FILE*
   std::FILE*
   fcookie(std::iostream& iostr)
   {
diff --git a/libdimensionxx/dimensionxx/canvas.hpp b/libdimensionxx/dimensionxx/canvas.hpp
index c501413..eda9ad3 100644
--- a/libdimensionxx/dimensionxx/canvas.hpp
+++ b/libdimensionxx/dimensionxx/canvas.hpp
@@ -21,29 +21,39 @@
 #ifndef DIMENSIONXX_CANVAS_HPP
 #define DIMENSIONXX_CANVAS_HPP
 
+// dmnsn_canvas* wrapper.
+
 namespace Dimension
 {
+  // Base canvas class.  Wraps a dmnsn_canvas*.
   class Canvas
   {
   public:
-    Canvas(unsigned int width, unsigned int height)
-      : m_canvas(dmnsn_new_canvas(width, height)) { }
+    // Allocate a dmnsn_canvas specified width and height.
+    Canvas(unsigned int width, unsigned int height);
+
+    // Wrap an existing canvas.
     explicit Canvas(dmnsn_canvas* canvas) : m_canvas(canvas) { }
+
+    // Delete the canvas.  (dmnsn_delete_canvas(m_canvas).)
     virtual ~Canvas();
 
-    unsigned int width()  const { return m_canvas->x; }
-    unsigned int height() const { return m_canvas->y; }
+    // Get the width and height.
+    unsigned int width() const;
+    unsigned int height() const;
 
-    Color pixel(unsigned int x, unsigned int y) const
-      { return Color(dmnsn_get_pixel(m_canvas, x, y)); }
-    void pixel(unsigned int x, unsigned int y, const Color& c)
-      { dmnsn_set_pixel(m_canvas, x, y, c.dmnsn()); }
+    // Get and set a pixel, thread-safely.
+    Color pixel(unsigned int x, unsigned int y) const;
+    void pixel(unsigned int x, unsigned int y, const Color& c);
 
-    dmnsn_canvas*       dmnsn()       { return m_canvas; }
-    const dmnsn_canvas* dmnsn() const { return m_canvas; }
+    // Access the wrapped C object.
+    dmnsn_canvas*       dmnsn();
+    const dmnsn_canvas* dmnsn() const;
 
   protected:
-    Canvas() : m_canvas(0) { }
+    // 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;
 
diff --git a/libdimensionxx/dimensionxx/color.hpp b/libdimensionxx/dimensionxx/color.hpp
index afd7ea5..a7087a7 100644
--- a/libdimensionxx/dimensionxx/color.hpp
+++ b/libdimensionxx/dimensionxx/color.hpp
@@ -21,16 +21,21 @@
 #ifndef DIMENSIONXX_COLOR_HPP
 #define DIMENSIONXX_COLOR_HPP
 
+// Wrappers for libdimension colors.
+
 namespace Dimension
 {
+  // Forward declarations
   class CIE_XYZ;
   class CIE_xyY;
   class CIE_Lab;
   class CIE_Luv;
   class sRGB;
 
+  // Default whitepoint (D50)
   extern const CIE_XYZ whitepoint;
 
+  // Wrapper for dmnsn_color
   class Color
   {
   public:
@@ -44,6 +49,7 @@ namespace Dimension
     // Color(const Color& c);
     // ~Color();
 
+    // Get and set filtered and unfiltered transparancy
     double filter() const { return m_color.filter; }
     double trans()  const { return m_color.trans; }
 
@@ -51,15 +57,20 @@ namespace Dimension
     double trans(double t)  { m_color.trans = t; }
 
     // Color& operator=(const Color& c);
+
+    // Add a color to this one in a perceptually correct manner
     Color& operator+=(const Color& c)
       { m_color = dmnsn_color_add(m_color, c.m_color); return *this; }
 
+    // Access the wrapped color
     dmnsn_color dmnsn() const { return m_color; }
 
   private:
     dmnsn_color m_color;
   };
 
+  // Wrappers for all libdimension color types
+
   class CIE_XYZ
   {
   public:
@@ -206,6 +217,7 @@ namespace Dimension
 
   // Color operators
 
+  // Perceptually correct color combination
   inline Color
   operator+(const Color& lhs, const Color& rhs)
   {
@@ -214,6 +226,7 @@ namespace Dimension
     return temp;
   }
 
+  // Perceptual color difference
   inline double
   operator-(const Color& lhs, const Color& rhs)
   {
diff --git a/libdimensionxx/dimensionxx/cookie.hpp b/libdimensionxx/dimensionxx/cookie.hpp
index acb783d..639fbfe 100644
--- a/libdimensionxx/dimensionxx/cookie.hpp
+++ b/libdimensionxx/dimensionxx/cookie.hpp
@@ -21,6 +21,9 @@
 #ifndef DIMENSIONXX_COOKIE_HPP
 #define DIMENSIONXX_COOKIE_HPP
 
+// Some internal magic to use C FILE* I/O with C++ streams.  Currently this ties
+// us to Linux and glibc, but in the future, this will be portable.
+
 #include <istream>
 #include <ostream>
 #include <cstdio>
diff --git a/libdimensionxx/dimensionxx/error.hpp b/libdimensionxx/dimensionxx/error.hpp
index 8919895..99670cb 100644
--- a/libdimensionxx/dimensionxx/error.hpp
+++ b/libdimensionxx/dimensionxx/error.hpp
@@ -21,21 +21,29 @@
 #ifndef DIMENSIONXX_ERROR_HPP
 #define DIMENSIONXX_ERROR_HPP
 
+// Wrappers for libdimension error handling, and an exception class.
+// dmnsn_error is still used by libdimensionxx whenever an exception shouldn't
+// be thrown, like in destructors, and whenever libdimension or libdimension-*
+// use it internally.  Exceptions are thrown otherwise to report errors.
+
 #include <dimension.h>
 #include <stdexcept>
 #include <string>
 
 namespace Dimension
 {
+  // Wrapper for dmnsn_severity
   enum Severity {
     SEVERITY_LOW    = DMNSN_SEVERITY_LOW,
     SEVERITY_MEDIUM = DMNSN_SEVERITY_MEDIUM,
     SEVERITY_HIGH   = DMNSN_SEVERITY_HIGH
   };
 
+  // Get or set the resilience, thread-safely
   Severity resilience();
   void resilience(Severity resilience);
 
+  // Generic exception class, derives from std::runtime_error
   class Dimension_Error : public std::runtime_error
   {
   public:
diff --git a/libdimensionxx/dimensionxx/geometry.hpp b/libdimensionxx/dimensionxx/geometry.hpp
index 4295c05..78b9b49 100644
--- a/libdimensionxx/dimensionxx/geometry.hpp
+++ b/libdimensionxx/dimensionxx/geometry.hpp
@@ -21,12 +21,15 @@
 #ifndef DIMENSIONXX_GEOMETRY_HPP
 #define DIMENSIONXX_GEOMETRY_HPP
 
+// Wrappers for geometric types (Scalars, Vectors, Lines (rays)).
+
 #include <dimension.h>
 
 namespace Dimension
 {
-  typedef dmnsn_scalar Scalar;
+  typedef dmnsn_scalar Scalar; // This is really `double'
 
+  // Wrapper for dmnsn_vector
   class Vector
   {
   public:
@@ -37,10 +40,13 @@ namespace Dimension
     // Vector(const Vector& v);
     // ~Vector();
 
+    // Get the x, y, and z components.
     Scalar x() const { return m_vector.x; }
     Scalar y() const { return m_vector.y; }
     Scalar z() const { return m_vector.z; }
 
+    // Vector arithmetic
+
     // Vector& operator=(const Vector& rhs);
     Vector& operator+=(const Vector& rhs)
       { m_vector = dmnsn_vector_add(m_vector, rhs.m_vector); return *this; }
@@ -51,12 +57,14 @@ namespace Dimension
     Vector& operator/=(Scalar rhs)
       { m_vector = dmnsn_vector_div(m_vector, rhs); return *this; }
 
+    // Get the wrapped vector
     dmnsn_vector dmnsn() const { return m_vector; }
 
   private:
     dmnsn_vector m_vector;
   };
 
+  // Wrapper for dmnsn_line
   class line
   {
   public:
@@ -70,8 +78,11 @@ namespace Dimension
     Vector n()  const { return Vector(m_line.n); }
 
     // line& operator=(const line& l);
+
+    // Get the point `t' on the line (x0 + t*n)
     Vector operator()(Scalar t) { return Vector(dmnsn_line_point(m_line, t)); }
 
+    // Get the wrapped line
     dmnsn_line dmnsn() const { return m_line; }
 
   private:
@@ -120,12 +131,14 @@ namespace Dimension
     return r;
   }
 
+  // Dot product
   inline Scalar
   dot(const Vector& lhs, const Vector& rhs)
   {
     return dmnsn_vector_dot(lhs.dmnsn(), rhs.dmnsn());
   }
 
+  // Cross product
   inline Vector
   cross(const Vector& lhs, const Vector& rhs)
   {
diff --git a/libdimensionxx/dimensionxx/png.hpp b/libdimensionxx/dimensionxx/png.hpp
index 96ab2ca..c14b25f 100644
--- a/libdimensionxx/dimensionxx/png.hpp
+++ b/libdimensionxx/dimensionxx/png.hpp
@@ -21,25 +21,43 @@
 #ifndef DIMENSIONXX_PNG_HPP
 #define DIMENSIONXX_PNG_HPP
 
+// C++ wrapper for libdimension-png.  PNG_Canvas derives from Canvas.
+
 #include <istream>
 #include <ostream>
 
 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
   {
   public:
+    // Input PNG_Canvas; read the Canvas from istr now
     explicit PNG_Canvas(std::istream& istr)
       : Canvas(), m_istr(&istr), m_ostr(0), m_written(false) { read(); }
+
+    // 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)
       : Canvas(x, y), m_istr(0), m_ostr(&ostr), m_written(false) { }
+
+    // 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)
       : Canvas(), m_istr(&istr), m_ostr(&ostr), m_written(false) { read(); }
+
+    // Call write() if we're an output PNG_Canvas, but trap any exceptions and
+    // report a dmnsn_error() instead.
     virtual ~PNG_Canvas();
 
+    // Write the Canvas to the output stream, throwing a Dimension_Error on
+    // error.
     void write();
 
   protected:
+    // In case a derived class needs to set m_canvas after we're constructed
     PNG_Canvas(std::ostream* ostr)
       : Canvas(), m_istr(0), m_ostr(ostr), m_written(false) { }
 
@@ -48,6 +66,8 @@ namespace Dimension
     std::ostream* m_ostr;
     bool m_written;
 
+    // Read the Canvas from a PNG file, and throw a Dimension_Error upon
+    // failure.
     void read();
 
     // Copying prohibited
diff --git a/libdimensionxx/error.cpp b/libdimensionxx/error.cpp
index 948a8c0..3d7dfa0 100644
--- a/libdimensionxx/error.cpp
+++ b/libdimensionxx/error.cpp
@@ -24,18 +24,21 @@
 
 namespace Dimension
 {
+  // Get the resilience, thread-safely, with dmnsn_get_resilience().
   Severity
   resilience()
   {
     return static_cast<Severity>(dmnsn_get_resilience());
   }
 
+  // Set the resilience, thread-safely, with dmnsn_set_resilience().
   void
   resilience(Severity resilience)
   {
     dmnsn_set_resilience(static_cast<dmnsn_severity>(resilience));
   }
 
+  // Dimension_Error constructor
   Dimension_Error::Dimension_Error(const std::string& str)
     : std::runtime_error(str) { }
 }
diff --git a/libdimensionxx/png.cpp b/libdimensionxx/png.cpp
index 1ca3047..348b7a7 100644
--- a/libdimensionxx/png.cpp
+++ b/libdimensionxx/png.cpp
@@ -25,6 +25,9 @@
 
 namespace Dimension
 {
+  // PNG_Canvas destructor.  Call write() to write the PNG file if not already
+  // written, but catch any exceptions and instead report the error with
+  // dmnsn_error() to avoid throwing from a destructor.
   PNG_Canvas::~PNG_Canvas()
   {
     if (m_ostr && !m_written) {
@@ -37,46 +40,60 @@ namespace Dimension
     }
   }
 
+  // Write the PNG file.  Uses the fcookie() interface to make a FILE*
+  // corresponding to an std::ostream (including std::ostringstream, etc).
   void PNG_Canvas::write()
   {
     if (m_written) {
+      // Does writing a PNG file twice make sense?
       throw Dimension_Error("Attempt to write canvas to PNG twice.");
     }
 
     if (!m_ostr) {
+      // Don't call write() if we're not an output PNG_Canvas...
       throw Dimension_Error("Attempt to write canvas to PNG without an output"
                             " stream.");
     }      
 
     FILE* file = fcookie(*m_ostr);
     if (!file) {
+      // fcookie() shouldn't fail, really
       throw Dimension_Error("Couldn't create C++/C IO interface when writing"
                             " canvas to PNG.");
     }      
 
+    // Write the PNG file
     if (dmnsn_png_write_canvas(m_canvas, file)) {
+      // The actual write operation failed, for some reason.
       std::fclose(file);
       throw Dimension_Error("Writing canvas to PNG failed.");
     }
 
     std::fclose(file);
-    m_written = true;
+    m_written = true; // We've written the file now, don't do it again
   }
 
+  // Read a canvas from a  PNG file.  Uses the fcookie() interface to make a
+  // FILE* corresponding to an std::istream (including std::istringstream, etc).
   void PNG_Canvas::read()
   {
     if (!m_istr) {
+      // read() is private, and only called from the appropriate constructors,
+      // so this REALLY shouldn't happen.
       throw Dimension_Error("Attempt to read canvas from PNG without an input"
                             " stream.");
     }      
 
     FILE* file = fcookie(*m_istr);
     if (!file) {
+      // fcookie() shouldn't fail, really
       throw Dimension_Error("Couldn't create C++/C IO interface when reading"
                             " canvas from PNG.");
     }      
 
+    // Read the canvas from a PNG file
     if (!(m_canvas = dmnsn_png_read_canvas(file))) {
+      // The read operation failed
       std::fclose(file);
       throw Dimension_Error("Reading canvas from PNG failed.");
     }