EomScrollView: Use better downscaling filter

Replace all instances of CAIRO_FILTER_BILINEAR with CAIRO_FILTER_GOOD.
This produces much less aliasing on downscaled images. CAIRO_FILTER_GOOD
uses the same method as CAIRO_FILTER_BILINEAR for scale factors greater
than 0.75, according to https://bugs.webkit.org/show_bug.cgi?id=147826.

Comparison screenshots made with eog 3.18.1: http://imgur.com/a/NaoOs

CAIRO_FILTER_BEST is better still, but the the visual difference is
almost imperceptible and the performance impact is severe.

https://bugzilla.gnome.org/show_bug.cgi?id=665897

origin commit: https://gitlab.gnome.org/GNOME/eog/commit/fbc1128

fixes #96

Author: yump

src/eom-scroll-view.c

@@ -1410,7 +1410,7 @@ eom_scroll_view_set_antialiasing_in (EomScrollView *view, gboolean state)
 
 	priv = view->priv;
 
-	new_interp_type = state ? CAIRO_FILTER_BILINEAR : CAIRO_FILTER_NEAREST;
+	new_interp_type = state ? CAIRO_FILTER_GOOD : CAIRO_FILTER_NEAREST;
 
 	if (priv->interp_type_in != new_interp_type) {
 		priv->interp_type_in = new_interp_type;
@@ -1429,7 +1429,7 @@ eom_scroll_view_set_antialiasing_out (EomScrollView *view, gboolean state)
 
 	priv = view->priv;
 
-	new_interp_type = state ? CAIRO_FILTER_BILINEAR : CAIRO_FILTER_NEAREST;
+	new_interp_type = state ? CAIRO_FILTER_GOOD : CAIRO_FILTER_NEAREST;
 
 	if (priv->interp_type_out != new_interp_type) {
 		priv->interp_type_out = new_interp_type;
@@ -1737,8 +1737,8 @@ eom_scroll_view_init (EomScrollView *view)
 	priv->min_zoom = MIN_ZOOM_FACTOR;
 	priv->zoom_mode = ZOOM_MODE_FIT;
 	priv->upscale = FALSE;
-	priv->interp_type_in = CAIRO_FILTER_BILINEAR;
-	priv->interp_type_out = CAIRO_FILTER_BILINEAR;
+	priv->interp_type_in = CAIRO_FILTER_GOOD;
+	priv->interp_type_out = CAIRO_FILTER_GOOD;
 	priv->scroll_wheel_zoom = FALSE;
 	priv->zoom_multiplier = IMAGE_VIEW_ZOOM_MULTIPLIER;
 	priv->image = NULL;