[gthumb] dragger: avoid some useless zoom

[Paolo Bacchilega <paobac src gnome org>]

commit 956810ce5220dcf42710121e67baabf389294970
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sun Oct 13 12:09:21 2013 +0200

    dragger: avoid some useless zoom

 gthumb/gth-image-dragger.c |   20 +++++++++++---------
 1 files changed, 11 insertions(+), 9 deletions(-)
---
diff --git a/gthumb/gth-image-dragger.c b/gthumb/gth-image-dragger.c
index 0c14c8f..7d94c0d 100644
--- a/gthumb/gth-image-dragger.c
+++ b/gthumb/gth-image-dragger.c
@@ -403,7 +403,8 @@ static void
 _gth_image_dragger_update_scaled_image (GthImageDragger *self)
 {
        cairo_surface_t *image;
-       double           zoom;
+       double           zoom_from_original;
+       double           zoom_from_image;
        int              image_width, image_height;
        int              original_width, original_height;
        int              new_width, new_height;
@@ -430,15 +431,16 @@ _gth_image_dragger_update_scaled_image (GthImageDragger *self)
        if (gth_image_viewer_get_zoom_quality (self->priv->viewer) == GTH_ZOOM_QUALITY_LOW)
                return;
 
-       zoom = gth_image_viewer_get_zoom (self->priv->viewer);
-       if (zoom >= 1.0)
-               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;
        image_width = cairo_image_surface_get_width (image);
        image_height = cairo_image_surface_get_height (image);
-       gth_image_viewer_get_original_size (self->priv->viewer, &original_width, &original_height);
-       new_width = zoom * original_width;
-       new_height = zoom * original_height;
+       zoom_from_image = (double) new_width / image_width;
+
+       if (zoom_from_image >= 1.0)
+               return;
 
        if (image_width * image_height <= SIZE_TOO_BIG_FOR_SCALE_BILINEAR) {
                self->priv->scaled = _cairo_image_surface_scale_bilinear (image, new_width, new_height);
@@ -447,7 +449,7 @@ _gth_image_dragger_update_scaled_image (GthImageDragger *self)
        else
                filter = SCALE_FILTER_BOX;
 
-       self->priv->scaled_zoom = zoom;
+       self->priv->scaled_zoom = zoom_from_original;
        _gth_image_dragger_create_scaled_high_quality (self, image, new_width, new_height, filter);
 }