Try the new target API first in VImage::write_to_buffer (#2511)

Needed after PR #2499.

cplusplus/VImage.cpp

@@ -714,16 +714,37 @@ VImage::write_to_buffer( const char *suffix, void **buf, size_t *size,
 	const char *operation_name;
 	VipsBlob *blob;
 
+	/* Save with the new target API if we can. Fall back to the older
+	 * mechanism in case the saver we need has not been converted yet.
+	 *
+	 * We need to hide any errors from this first phase.
+	 */
 	vips__filename_split8( suffix, filename, option_string );
-	if( !(operation_name = vips_foreign_find_save_buffer( filename )) ) {
+
-		delete options;
+	vips_error_freeze();
-		throw VError();
+	operation_name = vips_foreign_find_save_target( filename );
-	}
+	vips_error_thaw();
+
+	if( operation_name ) {
+		VTarget target = VTarget::new_to_memory();
 
+		call_option_string( operation_name, option_string,
+			(options ? options : VImage::option())->
+				set( "in", *this )->
+				set( "target", target ) );
+
+		g_object_get( target.get_target(), "blob", &blob, NULL );
+	}
+	else if( (operation_name = vips_foreign_find_save_buffer( filename )) ) {
 		call_option_string( operation_name, option_string,
 			(options ? options : VImage::option())->
 				set( "in", *this )->
 				set( "buffer", &blob ) );
+	}
+	else {
+		delete options;
+		throw VError();
+	}
 
 	if( blob ) {
 		if( buf ) {

cplusplus/examples/test.cpp

@@ -9,7 +9,7 @@
  *
  * run with:
  *
- * 	./a.out ~/pics/k2.jpg ~/pics/shark.jpg --vips-leak
+ * 	VIPS_LEAK=1 ./a.out ~/pics/k2.jpg ~/pics/shark.jpg
  * 	valgrind --leak-check=yes ./a.out ~/pics/k2.jpg ~/pics/shark.jpg 
  * 	rm x.tif
  *
@@ -295,6 +295,31 @@ main( int argc, char **argv )
 	g_free( buf ); 
 }
 
+{
+	// write to a formatted AVIF memory buffer
+	printf( "testing formatted AVIF memory write ...\n" );
+
+	if( vips_type_find("VipsOperation", "avifsave_target") != 0 ) {
+		size_t size;
+		void *buf;
+
+		// speed-up test by setting @effort to 0
+		left.write_to_buffer( ".avif", &buf, &size,
+			VImage::option()->set( "effort", 0 ) );
+		printf( "written to memory %p in AVIF format, %zu bytes\n", buf, size );
+
+		// load from the formatted memory area
+		VImage im = VImage::new_from_buffer( buf, size, "" );
+		printf( "loaded from memory, %d x %d pixel %s image\n",
+			im.width(), im.height(), im.get_string("heif-compression") );
+
+		g_free( buf );
+	}
+	else {
+		printf( "skipped, not compiled against libheif\n" );
+	}
+}
+
 {
 	// write to a vanilla memory buffer
 	printf( "testing memory array write ...\n" ); 

libvips/iofuncs/image.c

@@ -2678,7 +2678,7 @@ vips_image_write_to_file( VipsImage *image, const char *name, ... )
 	int result;
 
 	/* Save with the new target API if we can. Fall back to the older
-	 * mechanism in case the loader we need has not been converted yet.
+	 * mechanism in case the saver we need has not been converted yet.
 	 *
 	 * We need to hide any errors from this first phase.
 	 */