[gedit/wip/printing-enhancements] print-preview: do not store the dpi

[Sébastien Wilmet <swilmet src gnome org>]

commit 21d6c3bf14eb9d1fc7653127fd5fb3b493563f69
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sun Jun 28 16:21:13 2015 +0200

    print-preview: do not store the dpi
    
    It can be computed when needed. I don't think performance is important
    here. Except if there is a round trip between the X server and GDK to
    get the DPI. But I hope GDK does the caching for us.

 gedit/gedit-print-preview.c |   64 +++++++++++++++++++++++-------------------
 1 files changed, 35 insertions(+), 29 deletions(-)
---
diff --git a/gedit/gedit-print-preview.c b/gedit/gedit-print-preview.c
index 73b1ce8..6d40dfa 100644
--- a/gedit/gedit-print-preview.c
+++ b/gedit/gedit-print-preview.c
@@ -61,7 +61,6 @@ struct _GeditPrintPreview
         */
        GtkLayout *layout;
 
-       gdouble dpi;
        gdouble scale;
 
        /* multipage support */
@@ -142,6 +141,35 @@ gedit_print_preview_class_init (GeditPrintPreviewClass *klass)
        gtk_widget_class_bind_template_child (widget_class, GeditPrintPreview, layout);
 }
 
+static gdouble
+get_screen_dpi (GeditPrintPreview *preview)
+{
+       GdkScreen *screen;
+       gdouble dpi;
+       static gboolean warning_shown = FALSE;
+
+       screen = gtk_widget_get_screen (GTK_WIDGET (preview));
+
+       if (screen == NULL)
+       {
+               return PRINTER_DPI;
+       }
+
+       dpi = gdk_screen_get_resolution (screen);
+       if (dpi < 30.0 || 600.0 < dpi)
+       {
+               if (!warning_shown)
+               {
+                       g_warning ("Invalid the x-resolution for the screen, assuming 96dpi");
+                       warning_shown = TRUE;
+               }
+
+               dpi = 96.0;
+       }
+
+       return dpi;
+}
+
 /* Get the paper size in points: these must be used only
  * after the widget has been mapped and the dpi is known.
  */
@@ -154,7 +182,7 @@ get_paper_width (GeditPrintPreview *preview)
        page_setup = gtk_print_context_get_page_setup (preview->context);
        paper_width = gtk_page_setup_get_paper_width (page_setup, GTK_UNIT_INCH);
 
-       return paper_width * preview->dpi;
+       return paper_width * get_screen_dpi (preview);
 }
 
 static gdouble
@@ -166,7 +194,7 @@ get_paper_height (GeditPrintPreview *preview)
        page_setup = gtk_print_context_get_page_setup (preview->context);
        paper_height = gtk_page_setup_get_paper_height (page_setup, GTK_UNIT_INCH);
 
-       return paper_height * preview->dpi;
+       return paper_height * get_screen_dpi (preview);
 }
 
 /* The tile size is the size in pixels of the area where a page will be
@@ -788,7 +816,6 @@ static void
 gedit_print_preview_init (GeditPrintPreview *preview)
 {
        preview->cur_page = 0;
-       preview->dpi = PRINTER_DPI;
        preview->scale = 1.0;
        preview->n_columns = 1;
        preview->cursor_x = 0;
@@ -881,13 +908,13 @@ draw_page_content (cairo_t           *cr,
                   gint               page_number,
                   GeditPrintPreview *preview)
 {
+       gdouble dpi;
+
        /* scale to the desired size */
        cairo_scale (cr, preview->scale, preview->scale);
 
-       gtk_print_context_set_cairo_context (preview->context,
-                                            cr,
-                                            preview->dpi,
-                                            preview->dpi);
+       dpi = get_screen_dpi (preview);
+       gtk_print_context_set_cairo_context (preview->context, cr, dpi, dpi);
 
        gtk_print_operation_preview_render_page (preview->gtk_preview,
                                                 page_number);
@@ -993,24 +1020,6 @@ preview_draw (GtkWidget         *widget,
        return GDK_EVENT_STOP;
 }
 
-static gdouble
-get_screen_dpi (GeditPrintPreview *preview)
-{
-       GdkScreen *screen;
-       gdouble dpi;
-
-       screen = gtk_widget_get_screen (GTK_WIDGET (preview));
-
-       dpi = gdk_screen_get_resolution (screen);
-       if (dpi < 30.0 || 600.0 < dpi)
-       {
-               g_warning ("Invalid the x-resolution for the screen, assuming 96dpi");
-               dpi = 96.0;
-       }
-
-       return dpi;
-}
-
 static void
 set_n_pages (GeditPrintPreview *preview,
             gint               n_pages)
@@ -1035,9 +1044,6 @@ preview_ready (GtkPrintOperationPreview *gtk_preview,
        set_n_pages (preview, n_pages);
        goto_page (preview, 0);
 
-       /* figure out the dpi */
-       preview->dpi = get_screen_dpi (preview);
-
        set_zoom_factor (preview, 1.0);
 
        /* let the default gtklayout handler clear the background */