[gthumb/gthumb-3-10] image viewer: fixed bright line visual artifacts

[Paolo Bacchilega <paobac src gnome org>]

commit a0e318b146026b74a263f2c126c21a501128c2a6
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sun Nov 29 16:12:08 2020 +0100

    image viewer: fixed bright line visual artifacts
    
    Fixes https://gitlab.gnome.org/GNOME/gthumb/-/issues/118

 gthumb/gth-image-dragger.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gthumb/gth-image-dragger.c b/gthumb/gth-image-dragger.c
index 9eadbbfd..547958b6 100644
--- a/gthumb/gth-image-dragger.c
+++ b/gthumb/gth-image-dragger.c
@@ -588,8 +588,8 @@ _gth_image_dragger_update_scaled_image (GthImageDragger *self)
 
        zoom_from_original = gth_image_viewer_get_zoom (self->priv->viewer);
        gth_image_viewer_get_original_size (self->priv->viewer, &original_width, &original_height);
-       new_width = zoom_from_original * original_width * screen_scale_factor;
-       new_height = zoom_from_original * original_height * screen_scale_factor;
+       new_width = zoom_from_original * original_width * screen_scale_factor + 0.5;
+       new_height = zoom_from_original * original_height * screen_scale_factor + 0.5;
        image_width = cairo_image_surface_get_width (image);
        image_height = cairo_image_surface_get_height (image);
        zoom_from_image = (double) new_width / image_width;