C/C++ done

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ChangeLog

@@ -1,5 +1,7 @@
 15/4/17 started 8.6.0
 - supports fits images with leading non-image HDUs, thanks benepo
+- add vips_image_new_from_image() and vips_image_new_from_image1() ... make a
+  constant image
 
 23/4/17 started 8.5.5
 - doc polishing

TODO

@@ -1,3 +1,13 @@
+- can we change VImage::new_from_image() to not inherit bands? too awkward to
+  make a one-band image
+
+  needs some docs
+
+  add to python, C, ruby, php etc etc
+
+- does cpp image.bandjoin(12) work? how about 
+  bandjoin(std::vector<double>({1, 2}))
+
 - not sure about utf8 error messages on win
 
 - strange: 

cplusplus/VImage.cpp

@@ -565,34 +565,6 @@ VImage::new_from_buffer( void *buf, size_t len, const char *option_string,
 	return( out );
 }
 
-VImage 
-VImage::new_from_image( std::vector<double> pixel )
-{
-	VImage onepx = VImage::black( 1, 1, 
-		VImage::option()->set( "bands", bands() ) ); 
-
-	onepx = (onepx + pixel).cast( format() );
-
-	VImage big = onepx.embed( 0, 0, width(), height(), 
-		VImage::option()->set( "extend", VIPS_EXTEND_COPY ) ); 
-
-	big = big.copy( 
-		VImage::option()->
-			set( "interpretation", interpretation() )->
-			set( "xres", xres() )->
-			set( "yres", yres() )->
-			set( "xoffset", xres() )->
-			set( "yoffset", yres() ) ); 
-
-	return( big ); 
-}
-
-VImage 
-VImage::new_from_image( double pixel )
-{
-	return( new_from_image( to_vectorv( 1, pixel ) ) ); 
-}
-
 VImage 
 VImage::new_matrix( int width, int height ) 
 {
@@ -693,10 +665,10 @@ VImage::bandsplit( VOption *options )
 VImage 
 VImage::bandjoin( VImage other, VOption *options )
 {
-    VImage v[2] = { *this, other }; 
+	VImage v[2] = { *this, other }; 
-    std::vector<VImage> vec( v, v + VIPS_NUMBER( v ) );
+	std::vector<VImage> vec( v, v + VIPS_NUMBER( v ) );
 
-    return( bandjoin( vec, options ) ); 
+	return( bandjoin( vec, options ) ); 
 }
 
 std::complex<double> 

cplusplus/include/vips/VImage8.h

@@ -468,8 +468,21 @@ public:
 
 	static VImage new_matrixv( int width, int height, ... );
 
-	VImage new_from_image( std::vector<double> pixel );
+	VImage new_from_image( std::vector<double> pixel )
-	VImage new_from_image( double pixel );
+	{
+		VipsImage *image;
+
+		if( !(image = vips_image_new_from_image( this->get_image(), 
+			&pixel[0], pixel.size() )) )
+			throw( VError() ); 
+
+		return( VImage( image ) ); 
+	}
+
+	VImage new_from_image( double pixel )
+	{
+		return( new_from_image( to_vectorv( 1, pixel ) ) ); 
+	}
 
 	VImage write( VImage out );
 

doc/using-cpp.xml

@@ -134,11 +134,30 @@ main( int argc, char **argv )
 
       There are a series of similar constructors which parallel the other 
       constructors in the C API, see VImage::new_from_memory(),
-      VImage::new_from_buffer(), and VImage::new_matrix(). There's also 
+      VImage::new_from_buffer(), and VImage::new_matrix(). 
+    </para>
+
+    <para>
+      The convenience function `VImage::new_from_image()` makes a constant 
+      image from an existing image. The image it returns will have the same 
+      size, interpretation, resolution and format as the image you call it on, 
+      but with every pixel having the constant value you specify. For example:
+
+<programlisting language="cpp">
+      new_image = image.new_from_image(12);
+</programlisting>
+
+      Now `new_image` has the same size as `image`, but has one band, and every 
+      pixel has the value 12. You can pass a `std::vector<double>` as the 
+      argument to make a constant image with a different number of bands. 
+    </para>
+
+    <para>
+      There's also 
       VImage::new_memory() and VImage::new_temp_file(), which when written to 
       with VImage::write() will create whole images on memory or on disc. 
     </para>
-    
+
     <para>
       The next line finds the average pixel value, it's the equivalent of the 
       vips_avg() function. The differences from the C API are:

libvips/include/vips/image.h

@@ -452,6 +452,9 @@ VipsImage *vips_image_new_matrix_from_array( int width, int height,
 	const double *array, int size );
 VipsImage *vips_image_matrix_from_array( int width, int height, 
 	const double *array, int size );
+VipsImage *vips_image_new_from_image( VipsImage *image, const double *c, int n );
+VipsImage *vips_image_new_from_image1( VipsImage *image, double c );
+
 void vips_image_set_delete_on_close( VipsImage *image, 
 	gboolean delete_on_close );
 guint64 vips_get_disc_threshold( void );

libvips/iofuncs/image.c

@@ -2292,6 +2292,80 @@ vips_image_matrix_from_array( int width, int height,
 		array, size ) ); 
 }
 
+/**
+ * vips_image_new_from_image:
+ * @image: image to copy
+ * @c: (array length=n) (transfer none): array of constants
+ * @n: number of constants
+ *
+ * Creates a new image with width, height, format, interpretation, resolution
+ * and offset taken from @image, but with number of bands taken from @n and the
+ * value of each band element set from @c.
+ *
+ * See also: vips_image_new_from_image1()
+ *
+ * Returns: (transfer full): the new #VipsImage, or %NULL on error.
+ */
+VipsImage *
+vips_image_new_from_image( VipsImage *image, const double *c, int n )
+{
+	VipsObject *scope = (VipsObject *) vips_image_new();
+	VipsImage **t = (VipsImage **) vips_object_local_array( scope, 5 );
+
+	double *ones;
+	int i;
+	VipsImage *result;
+
+	if( !(ones = VIPS_ARRAY( scope, n, double )) ) {
+		g_object_unref( scope );
+		return( NULL );
+	}
+	for( i = 0; i < n; i++ )
+		ones[i] = 1.0;
+
+	if( vips_black( &t[0], 1, 1, NULL ) ||
+		vips_linear( t[0], &t[1], ones, (double *) c, n, NULL ) ||
+		vips_cast( t[1], &t[2], image->BandFmt, NULL ) ||
+		vips_embed( t[2], &t[3], 0, 0, image->Xsize, image->Ysize,
+			"extend", VIPS_EXTEND_COPY, NULL ) ||
+		vips_copy( t[3], &t[4], 
+			"interpretation", image->Type,
+			"xres", image->Xres,
+			"yres", image->Yres,
+			"xoffset", image->Xoffset,
+			"yoffset", image->Yoffset,
+			NULL ) ) {
+		g_object_unref( scope );
+		return( NULL );
+	}
+
+	result = t[4];
+	g_object_ref( result );
+
+	g_object_unref( scope );
+
+	return( result ); 
+}
+
+/**
+ * vips_image_new_from_image1:
+ * @image: image to copy
+ * @c: constants
+ *
+ * Creates a new image with width, height, format, interpretation, resolution
+ * and offset taken from @image, but with one band and each pixel having the
+ * value @c.
+ *
+ * See also: vips_image_new_from_image()
+ *
+ * Returns: (transfer full): the new #VipsImage, or %NULL on error.
+ */
+VipsImage *
+vips_image_new_from_image1( VipsImage *image, double c )
+{
+	return( vips_image_new_from_image( image, (const double *) &c, 1 ) );
+}
+
 /**
  * vips_image_set_delete_on_close:
  * @image: image to set