[gthumb] image viewer: use a white background for transparency

[Paolo Bacchilega <paobac src gnome org>]

commit 57df6d225a6dd24f2864ee081a533294c50dc27b
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Thu Oct 26 08:52:54 2017 +0200

    image viewer: use a white background for transparency
    
    [bug #780207]

 gthumb/gth-image-viewer.c |   94 +++++++++++++++++++++-----------------------
 1 files changed, 45 insertions(+), 49 deletions(-)
---
diff --git a/gthumb/gth-image-viewer.c b/gthumb/gth-image-viewer.c
index ee95894..1b9747d 100644
--- a/gthumb/gth-image-viewer.c
+++ b/gthumb/gth-image-viewer.c
@@ -806,24 +806,6 @@ queue_animation_frame_change (GthImageViewer *self)
 
 
 static gboolean
-image_has_alpha (GthImageViewer *viewer)
-{
-       cairo_surface_t *image;
-       guchar          *first_pixel;
-
-       image = gth_image_viewer_get_current_image (viewer);
-       if (image == NULL)
-               return FALSE;
-
-       first_pixel = _cairo_image_surface_flush_and_get_data (image);
-       if (first_pixel == NULL)
-               return FALSE;
-
-       return first_pixel[CAIRO_ALPHA] < 255;
-}
-
-
-static gboolean
 gth_image_viewer_draw (GtkWidget *widget,
                       cairo_t   *cr)
 {
@@ -2632,50 +2614,64 @@ gth_image_viewer_paint_background (GthImageViewer *self,
 }
 
 
+#define FRAME_SHADOW_OFS 1
+
+
 void
 gth_image_viewer_paint_frame (GthImageViewer *self,
                              cairo_t        *cr)
 {
-       if (! gth_image_viewer_is_frame_visible (self)
-           || gth_image_viewer_is_animation (self)
-           || image_has_alpha (self))
-       {
-               return;
-       }
+       gboolean background_only;
+
+       background_only = ! gth_image_viewer_is_frame_visible (self);
 
        cairo_save (cr);
 
        cairo_translate (cr, -self->visible_area.x, -self->visible_area.y);
 
-       /* drop shadow */
+       if (! background_only) {
+               /* drop shadow */
 
-       cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 0.5);
-       cairo_rectangle (cr,
-                        self->image_area.x + 2 + 0.5,
-                        self->image_area.y + 2 + 0.5,
-                        self->image_area.width + 2,
-                        self->image_area.height + 2);
-       cairo_fill (cr);
+               cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 0.5);
+               cairo_rectangle (cr,
+                                self->image_area.x + FRAME_SHADOW_OFS + 0.5,
+                                self->image_area.y + FRAME_SHADOW_OFS + 0.5,
+                                self->image_area.width + 2 + FRAME_SHADOW_OFS,
+                                self->image_area.height + 2 + FRAME_SHADOW_OFS);
+               cairo_fill (cr);
+       }
 
-       /* frame */
+       /* background */
 
-       cairo_set_line_width (cr, 2.0);
-       cairo_set_source_rgb (cr, 1.0, 1.0, 1.0);
-       cairo_rectangle (cr,
-                        self->image_area.x - 1,
-                        self->image_area.y - 1,
-                        self->image_area.width + 2,
-                        self->image_area.height + 2);
-       cairo_stroke (cr);
-
-       cairo_set_line_width (cr, 1.0);
-       cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
+       cairo_set_source_rgba (cr, 1.0, 1.0, 1.0, 1.0);
        cairo_rectangle (cr,
-                        self->image_area.x - 2,
-                        self->image_area.y - 2,
-                        self->image_area.width + 5,
-                        self->image_area.height + 5);
-       cairo_stroke (cr);
+                        self->image_area.x,
+                        self->image_area.y,
+                        self->image_area.width,
+                        self->image_area.height);
+       cairo_fill (cr);
+
+       if (! background_only) {
+               /* frame */
+
+               cairo_set_line_width (cr, 2.0);
+               cairo_set_source_rgb (cr, 1.0, 1.0, 1.0);
+               cairo_rectangle (cr,
+                                self->image_area.x - 1,
+                                self->image_area.y - 1,
+                                self->image_area.width + 2,
+                                self->image_area.height + 2);
+               cairo_stroke (cr);
+
+               cairo_set_line_width (cr, 1.0);
+               cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
+               cairo_rectangle (cr,
+                                self->image_area.x - 2,
+                                self->image_area.y - 2,
+                                self->image_area.width + 5,
+                                self->image_area.height + 5);
+               cairo_stroke (cr);
+       }
 
        cairo_restore (cr);
 }