[gthumb] "High" quality zoom is pixelated on hi-dpi monitors

[Paolo Bacchilega <paobac src gnome org>]

commit e157afe353027b17bf6ce0a1ccdd02af09650d21
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Wed Oct 25 19:02:56 2017 +0200

    "High" quality zoom is pixelated on hi-dpi monitors
    
    [bug #779340]

 extensions/image_viewer/gth-image-viewer-page.c |    4 ++--
 gthumb/gth-image-dragger.c                      |   11 +++++++----
 2 files changed, 9 insertions(+), 6 deletions(-)
---
diff --git a/extensions/image_viewer/gth-image-viewer-page.c b/extensions/image_viewer/gth-image-viewer-page.c
index 33b62ca..f081c20 100644
--- a/extensions/image_viewer/gth-image-viewer-page.c
+++ b/extensions/image_viewer/gth-image-viewer-page.c
@@ -170,7 +170,7 @@ _gth_image_preloader_get_requested_size_for_next_images (GthImageViewerPage *sel
                break;
        }
 
-       return requested_size;
+       return requested_size * gtk_widget_get_scale_factor (GTK_WIDGET (self->priv->viewer));
 }
 
 
@@ -201,7 +201,7 @@ _gth_image_preloader_get_requested_size_for_current_image (GthImageViewerPage *s
                break;
        }
 
-       return requested_size;
+       return requested_size * gtk_widget_get_scale_factor (GTK_WIDGET (self->priv->viewer));
 }
 
 
diff --git a/gthumb/gth-image-dragger.c b/gthumb/gth-image-dragger.c
index 546c766..aad7630 100644
--- a/gthumb/gth-image-dragger.c
+++ b/gthumb/gth-image-dragger.c
@@ -493,6 +493,7 @@ _gth_image_dragger_update_scaled_image (GthImageDragger *self)
        int              image_width, image_height;
        int              original_width, original_height;
        int              new_width, new_height;
+       int              screen_scale_factor;
        scale_filter_t   filter;
 
        self->priv->scaled_zoom = 0;
@@ -517,20 +518,22 @@ _gth_image_dragger_update_scaled_image (GthImageDragger *self)
                return;
        }
 
-       if (gth_image_viewer_get_zoom_quality_filter (self->priv->viewer) == CAIRO_FILTER_FAST) {
+       screen_scale_factor = gtk_widget_get_scale_factor (GTK_WIDGET (self->priv->viewer));
+
+       if ((screen_scale_factor == 1) && (gth_image_viewer_get_zoom_quality_filter (self->priv->viewer) == 
CAIRO_FILTER_FAST)) {
                gtk_widget_queue_draw (GTK_WIDGET (self->priv->viewer));
                return;
        }
 
        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;
-       new_height = zoom_from_original * original_height;
+       new_width = zoom_from_original * original_width * screen_scale_factor;
+       new_height = zoom_from_original * original_height * screen_scale_factor;
        image_width = cairo_image_surface_get_width (image);
        image_height = cairo_image_surface_get_height (image);
        zoom_from_image = (double) new_width / image_width;
 
-       if (zoom_from_image >= 1.0) {
+       if ((screen_scale_factor == 1) && (zoom_from_image >= 1.0)) {
                gtk_widget_queue_draw (GTK_WIDGET (self->priv->viewer));
                return;
        }