[gthumb] slideshow: use black for transparency

[Paolo Bacchilega <paobac src gnome org>]

commit 313f7bf76cab69aadc46102c3e6e590e3171dad5
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Tue Nov 5 10:35:53 2019 +0100

    slideshow: use black for transparency

 extensions/slideshow/gth-slideshow.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/extensions/slideshow/gth-slideshow.c b/extensions/slideshow/gth-slideshow.c
index 769d3f1d..30935c94 100644
--- a/extensions/slideshow/gth-slideshow.c
+++ b/extensions/slideshow/gth-slideshow.c
@@ -744,6 +744,7 @@ default_projector_construct (GthSlideshow *self)
        gth_image_viewer_set_zoom_change (GTH_IMAGE_VIEWER (self->priv->viewer), GTH_ZOOM_CHANGE_FIT_SIZE);
        gth_image_viewer_set_zoom_quality (GTH_IMAGE_VIEWER (self->priv->viewer), GTH_ZOOM_QUALITY_LOW);
        gth_image_viewer_add_painter (GTH_IMAGE_VIEWER (self->priv->viewer), default_projector_pause_painter, 
self);
+       gth_image_viewer_set_transparency_style (GTH_IMAGE_VIEWER (self->priv->viewer), 
GTH_TRANSPARENCY_STYLE_BLACK);
 
        g_signal_connect (self->priv->viewer, "button-press-event", G_CALLBACK (viewer_event_cb), self);
        g_signal_connect (self->priv->viewer, "motion-notify-event", G_CALLBACK (viewer_event_cb), self);