add gif background colour as metadata

ChangeLog

@@ -17,8 +17,9 @@
 - hist_find outputs a double histogram for large images [erdmann]
 - fix ref leaks in mosaicing package
 - run libvips leak test in CI 
-- add vips_fitsload_source()m vips_niftiload_source()
-- png load notes background colour as metadata [781545872]
+- add vips_fitsload_source(), vips_niftiload_source()
+- png and gif load note background colour as metadata [781545872]
+- add vips_image_[set|get]_array_double()
 
 22/12/20 start 8.10.6
 - don't seek on bad file descriptors [kleisauke]

libvips/foreign/gifload.c

@@ -42,6 +42,8 @@
  * 2/7/20
  * 	- clip out of bounds images against canvas
  * 	- fix PREVIOUS handling, again
+ * 19/2/21 781545872
+ * 	- read out background, if we can
  */
 
 /*
@@ -701,6 +703,7 @@ static int
 vips_foreign_load_gif_set_header( VipsForeignLoadGif *gif, VipsImage *image )
 {
 	const gint64 total_height = (gint64) gif->file->SHeight * gif->n;
+	ColorMapObject *map = gif->file->SColorMap;
 
 	if( total_height <= 0 || 
 		total_height > VIPS_MAX_COORD ) {
@@ -745,6 +748,18 @@ vips_foreign_load_gif_set_header( VipsForeignLoadGif *gif, VipsImage *image )
 	if( gif->comment )
 		vips_image_set_string( image, "gif-comment", gif->comment );
 
+	if( map && 
+		gif->file->SBackGroundColor >= 0 &&
+		gif->file->SBackGroundColor < map->ColorCount ) { 
+		double array[3];
+
+		array[0] = map->Colors[gif->file->SBackGroundColor].Red;
+		array[1] = map->Colors[gif->file->SBackGroundColor].Green;
+		array[2] = map->Colors[gif->file->SBackGroundColor].Blue;
+
+		vips_image_set_array_double( image, "background", array, 3 );
+	}
+
 	return( 0 );
 }
 

libvips/foreign/spngload.c

@@ -302,14 +302,9 @@ vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 			break;
 		}
 
-		if( n > 0 ) {
-			GValue value = { 0 };
-
-			g_value_init( &value, VIPS_TYPE_ARRAY_DOUBLE );
-			vips_value_set_array_double( &value, array, n );
-			vips_image_set( image, "background", &value );
-			g_value_unset( &value );
-		}
+		if( n > 0 ) 
+			vips_image_set_array_double( image, "background", 
+				array, n );
 	}
 }
 

libvips/foreign/vipspng.c

@@ -597,14 +597,9 @@ png2vips_header( Read *read, VipsImage *out )
 			break;
 		}
 
-		if( n > 0 ) {
-			GValue value = { 0 };
-
-			g_value_init( &value, VIPS_TYPE_ARRAY_DOUBLE );
-			vips_value_set_array_double( &value, array, n );
-			vips_image_set( out, "background", &value );
-			g_value_unset( &value );
-		}
+		if( n > 0 )
+			vips_image_set_array_double( out, "background", 
+				array, n );
 	}
 }
 #endif

libvips/include/vips/header.h

@@ -230,6 +230,10 @@ void vips_image_set_array_int( VipsImage *image, const char *name,
 	const int *array, int n );
 int vips_image_get_array_int( VipsImage *image, const char *name, 
 	int **out, int *n );
+int vips_image_get_array_double( VipsImage *image, const char *name, 
+	double **out, int *n );
+void vips_image_set_array_double( VipsImage *image, const char *name,
+	const double *array, int n );
 
 int vips_image_history_printf( VipsImage *image, const char *format, ... )
 	__attribute__((format(printf, 2, 3)));

libvips/iofuncs/header.c

@@ -1959,6 +1959,64 @@ vips_image_set_array_int( VipsImage *image, const char *name,
 	g_value_unset( &value );
 }
 
+/** 
+ * vips_image_get_array_double: (method)
+ * @image: image to get the metadata from
+ * @name: metadata name
+ * @out: (transfer none): return pointer to array
+ * @n: (allow-none): return the number of elements here, optionally
+ *
+ * Gets @out from @im under the name @name. 
+ * The field must be of type
+ * #VIPS_TYPE_ARRAY_INT.
+ *
+ * Do not free @out. @out is valid as long as @image is valid.
+ *
+ * Use vips_image_get_typeof() to test for the 
+ * existence of a piece of metadata.
+ *
+ * See also: vips_image_get(), vips_image_set_image()
+ *
+ * Returns: 0 on success, -1 otherwise.
+ */
+int
+vips_image_get_array_double( VipsImage *image, const char *name,
+	double **out, int *n )
+{
+	GValue value = { 0 };
+
+	if( meta_get_value( image, name, VIPS_TYPE_ARRAY_DOUBLE, &value ) ) 
+		return( -1 );
+	*out = vips_value_get_array_double( &value, n );
+	g_value_unset( &value );
+
+	return( 0 );
+}
+
+/**
+ * vips_image_set_array_double: (method)
+ * @image: image to attach the metadata to
+ * @name: metadata name
+ * @array: (array length=n) (allow-none): array of doubles
+ * @n: the number of elements 
+ *
+ * Attaches @array as a metadata item on @image as @name. 
+ * A convenience function over vips_image_set().
+ *
+ * See also: vips_image_get_image(), vips_image_set().
+ */
+void
+vips_image_set_array_double( VipsImage *image, const char *name,
+	const double *array, int n )
+{
+	GValue value = { 0 };
+
+	g_value_init( &value, VIPS_TYPE_ARRAY_DOUBLE );
+	vips_value_set_array_double( &value, array, n );
+	vips_image_set( image, name, &value );
+	g_value_unset( &value );
+}
+
 /**
  * vips_image_history_printf: (method)
  * @image: add history line to this image