zoom: fix zoom

Right now zoom only works on the output at 0, 0 because it's adding
the output corner co-ordinates to global co-ordinates that already
include the output offset.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Bryce Harrington <b.harrington@samsung.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

src/zoom.c

@@ -96,8 +96,8 @@ weston_output_update_zoom_transform(struct weston_output *output)
 	global_x = wl_fixed_to_double(x);
 	global_y = wl_fixed_to_double(y);
 
-	output->zoom.trans_x = global_x - (output->x + output->width / 2);
+	output->zoom.trans_x = global_x - output->width / 2;
-	output->zoom.trans_y = global_y - (output->y + output->height / 2);
+	output->zoom.trans_y = global_y - output->height / 2;
 
 	if (output->zoom.trans_x < 0)
 		output->zoom.trans_x = 0;