improve C++ API

Make VObject inheritance public, so we can have a single set() for all
VObject-derived types.

ChangeLog

@@ -1,5 +1,8 @@
 14/8/20 started 8.11
 - add vips_jpegload_source() and vips_svgload_source() to public C API
+- integrate doxygen in build system to generate C++ API docs
+- improve C++ API doc comments
+- add VipsInterpolate and guint64 support to C++ API 
 
 9/8/20 started 8.10.1
 - fix markdown -> xml conversion in doc generation

cplusplus/VConnection.cpp

@@ -110,19 +110,6 @@ VSource::new_from_options( const char *options )
 	return( out ); 
 }
 
-VOption *
-VOption::set( const char *name, const VSource value )
-{
-	Pair *pair = new Pair( name );
-
-	pair->input = true;
-	g_value_init( &pair->value, VIPS_TYPE_SOURCE );
-	g_value_set_object( &pair->value, value.get_source() );
-	options.push_back( pair );
-
-	return( this );
-}
-
 VTarget 
 VTarget::new_to_descriptor( int descriptor )
 {
@@ -162,17 +149,4 @@ VTarget::new_to_memory()
 	return( out ); 
 }
 
-VOption *
-VOption::set( const char *name, const VTarget value )
-{
-	Pair *pair = new Pair( name );
-
-	pair->input = true;
-	g_value_init( &pair->value, VIPS_TYPE_TARGET );
-	g_value_set_object( &pair->value, value.get_target() );
-	options.push_back( pair );
-
-	return( this );
-}
-
 VIPS_NAMESPACE_END

cplusplus/VImage.cpp

@@ -140,20 +140,6 @@ VOption::set( const char *name, int value )
 	return( this );
 }
 
-// input double
-VOption *
-VOption::set( const char *name, double value )
-{
-	Pair *pair = new Pair( name );
-
-	pair->input = true;
-	g_value_init( &pair->value, G_TYPE_DOUBLE );
-	g_value_set_double( &pair->value, value );
-	options.push_back( pair );
-
-	return( this );
-}
-
 // input guint64
 VOption *
 VOption::set( const char *name, guint64 value )
@@ -168,6 +154,20 @@ VOption::set( const char *name, guint64 value )
 	return( this );
 }
 
+// input double
+VOption *
+VOption::set( const char *name, double value )
+{
+	Pair *pair = new Pair( name );
+
+	pair->input = true;
+	g_value_init( &pair->value, G_TYPE_DOUBLE );
+	g_value_set_double( &pair->value, value );
+	options.push_back( pair );
+
+	return( this );
+}
+
 VOption *
 VOption::set( const char *name, const char *value )
 {
@@ -181,39 +181,17 @@ VOption::set( const char *name, const char *value )
 	return( this );
 }
 
-// input image
+// input vips object (image, source, target, etc. etc.)
 VOption *
-VOption::set( const char *name, const VImage value )
+VOption::set( const char *name, const VObject value )
 {
 	Pair *pair = new Pair( name );
+	VipsObject *object = value.get_object();
+	GType type = G_VALUE_TYPE( object );
 
 	pair->input = true;
-	g_value_init( &pair->value, VIPS_TYPE_IMAGE );
+	g_value_init( &pair->value, type );
-	g_value_set_object( &pair->value, value.get_image() );
+	g_value_set_object( &pair->value, object );
-	options.push_back( pair );
-
-	return( this );
-}
-
-// input double array
-VOption *
-VOption::set( const char *name, std::vector<double> value )
-{
-	Pair *pair = new Pair( name );
-
-	double *array;
-	unsigned int i;
-
-	pair->input = true;
-
-	g_value_init( &pair->value, VIPS_TYPE_ARRAY_DOUBLE );
-	vips_value_set_array_double( &pair->value, NULL,
-		static_cast< int >( value.size() ) );
-	array = vips_value_get_array_double( &pair->value, NULL );
-
-	for( i = 0; i < value.size(); i++ ) 
-		array[i] = value[i];
-
 	options.push_back( pair );
 
 	return( this );
@@ -243,6 +221,30 @@ VOption::set( const char *name, std::vector<int> value )
 	return( this );
 }
 
+// input double array
+VOption *
+VOption::set( const char *name, std::vector<double> value )
+{
+	Pair *pair = new Pair( name );
+
+	double *array;
+	unsigned int i;
+
+	pair->input = true;
+
+	g_value_init( &pair->value, VIPS_TYPE_ARRAY_DOUBLE );
+	vips_value_set_array_double( &pair->value, NULL,
+		static_cast< int >( value.size() ) );
+	array = vips_value_get_array_double( &pair->value, NULL );
+
+	for( i = 0; i < value.size(); i++ ) 
+		array[i] = value[i];
+
+	options.push_back( pair );
+
+	return( this );
+}
+
 // input image array
 VOption *
 VOption::set( const char *name, std::vector<VImage> value )

cplusplus/VInterpolate.cpp

@@ -60,17 +60,4 @@ VInterpolate::new_from_name( const char *name, VOption *options )
 	return( out ); 
 }
 
-VOption *
-VOption::set( const char *name, const VInterpolate value )
-{
-	Pair *pair = new Pair( name );
-
-	pair->input = true;
-	g_value_init( &pair->value, VIPS_TYPE_INTERPOLATE );
-	g_value_set_object( &pair->value, value.get_interpolate() );
-	options.push_back( pair );
-
-	return( this );
-}
-
 VIPS_NAMESPACE_END

cplusplus/include/vips/VConnection8.h

@@ -34,7 +34,7 @@
 
 VIPS_NAMESPACE_START
 
-class VSource : VObject
+class VSource : public VObject
 {
 public:
 	VSource( VipsSource *input, VSteal steal = STEAL ) : 
@@ -66,7 +66,7 @@ public:
 
 };
 
-class VTarget : VObject
+class VTarget : public VObject
 {
 public:
 	VTarget( VipsTarget *output, VSteal steal = STEAL ) : 

cplusplus/include/vips/VImage8.h

@@ -223,13 +223,10 @@ public:
 	VOption *set( const char *name, guint64 value );
 	VOption *set( const char *name, double value );
 	VOption *set( const char *name, const char *value );
-	VOption *set( const char *name, const VImage value );
+	VOption *set( const char *name, const VObject value );
-	VOption *set( const char *name, const VInterpolate value ); 
-	VOption *set( const char *name, const VSource value );
-	VOption *set( const char *name, const VTarget value );
-	VOption *set( const char *name, std::vector<VImage> value );
-	VOption *set( const char *name, std::vector<double> value );
 	VOption *set( const char *name, std::vector<int> value );
+	VOption *set( const char *name, std::vector<double> value );
+	VOption *set( const char *name, std::vector<VImage> value );
 	VOption *set( const char *name, VipsBlob *value ); 
 
 	VOption *set( const char *name, bool *value ); 
@@ -244,7 +241,7 @@ public:
 
 };
 
-class VImage : VObject
+class VImage : public VObject
 {
 public:
 	using VObject::is_null;

cplusplus/include/vips/VInterpolate8.h

@@ -41,7 +41,7 @@ VIPS_NAMESPACE_START
  * The available interpolators vary a bit with your libvips version and how it
  * was built, but will include `nearest`, `bilinear` and `bicubic`.
  */
-class VInterpolate : VObject
+class VInterpolate : public VObject
 {
 public:
 	/**