[gnome-boxes] util-app: Add paint_empty_frame()

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit 3a6620a62f4268251666579ba4b173cf8e8ac1c5
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Tue Jun 23 12:23:05 2015 +0200

    util-app: Add paint_empty_frame()
    
    Add the paint_empty_frame() function, allowing to draw a rounded
    rectangle with a border.
    
    This will be used in next commit to draw a better thumbnail for stopped
    boxes to better differenciate them from running ones with (mostly) black
    thumbnails (e.g full screened terminal windows).
    
    https://bugzilla.gnome.org/show_bug.cgi?id=730258

 src/util-app.vala |   41 +++++++++++++++++++++++++++++++++++++++++
 1 files changed, 41 insertions(+), 0 deletions(-)
---
diff --git a/src/util-app.vala b/src/util-app.vala
index ddc4ce4..3acc449 100644
--- a/src/util-app.vala
+++ b/src/util-app.vala
@@ -514,4 +514,45 @@ namespace Boxes {
 
         return pix;
     }
+
+    public Gdk.Pixbuf? paint_empty_frame (int width, int height, double radius, Gdk.RGBA border_color, 
Gdk.RGBA? bg_color) {
+        var surface = new Cairo.ImageSurface (Cairo.Format.ARGB32, width, height);
+        var cr = new Cairo.Context (surface);
+
+        if (bg_color != null) {
+            cr.set_source_rgba (bg_color.red, bg_color.green, bg_color.blue, bg_color.alpha);
+            paint_frame_background (cr, width, height, radius);
+        }
+
+        cr.set_source_rgba (border_color.red, border_color.green, border_color.blue, border_color.alpha);
+        paint_frame_border (cr, width, height, radius);
+
+        return Gdk.pixbuf_get_from_surface (surface, 0, 0, width, height);
+    }
+
+    private void paint_frame_background (Cairo.Context cr, int width, int height, double radius) {
+        rounded_rectangle (cr, 0.5, 0.5, width - 1, height - 1, radius);
+        cr.fill ();
+    }
+
+    private void paint_frame_border (Cairo.Context cr, int width, int height, double radius) {
+        cr.set_line_width (1.0);
+        // The rectangle is reduced by 0.5px on each side to allow drawing a sharp 1px line and not between 
two pixels.
+        rounded_rectangle (cr, 0.5, 0.5, width - 1, height - 1, radius);
+        cr.stroke ();
+    }
+
+    private void rounded_rectangle (Cairo.Context cr, double x, double y, double width, double height, 
double radius) {
+        const double ARC_0 = 0;
+        const double ARC_1 = Math.PI * 0.5;
+        const double ARC_2 = Math.PI;
+        const double ARC_3 = Math.PI * 1.5;
+
+        cr.new_sub_path ();
+        cr.arc (x + width - radius, y + radius,          radius, ARC_3, ARC_0);
+        cr.arc (x + width - radius, y + height - radius, radius, ARC_0, ARC_1);
+        cr.arc (x + radius,         y + height - radius, radius, ARC_1, ARC_2);
+        cr.arc (x + radius,         y + radius,          radius, ARC_2, ARC_3);
+        cr.close_path ();
+    }
 }