Port CreateMissingImage() to GTK3.

Pinta.Core/Extensions/CairoExtensions.cs

@@ -729,6 +729,7 @@ public static bool ContainsPoint (this Cairo.Rectangle r, Cairo.PointD point)
 
 		public unsafe static Gdk.Pixbuf ToPixbuf (this Cairo.ImageSurface surfSource)
 		{
+			// TODO-GTK3 use Gdk.Pixbuf.GetFromSurface once available (https://github.com/GtkSharp/GtkSharp/issues/174)
 			using (Cairo.ImageSurface surf = surfSource.Clone ()) {
 				surf.Flush ();
 

Pinta.Effects/CoreEffectsExtension.cs

@@ -32,7 +32,7 @@
 
 namespace Pinta.Effects
 {
-	// TODO-GTK3
+	// TODO-GTK3 (addins)
 #if false
 	[Mono.Addins.Extension]
 	class CoreEffectsExtension : IExtension

Pinta.Effects/Utilities/EffectHelper.cs

@@ -41,7 +41,7 @@ public static class EffectHelper
         /// The localizer for the effect add-in. This is used to fetch translations for the
         /// strings in the dialog.
         /// </param>
-        // TODO-GTK3
+        // TODO-GTK3 (addins)
 #if false
 		public static bool LaunchSimpleEffectDialog (BaseEffect effect, AddinLocalizer localizer)
 		{

Pinta.Resources/ResourceManager.cs

@@ -108,26 +108,29 @@ public static Stream GetResourceIconStream (string name)
 		// https://github.com/mono/monodevelop/blob/master/main/src/core/MonoDevelop.Ide/gtk-gui/generated.cs
 		private static Pixbuf CreateMissingImage (int size)
 		{
-			// TODO-GTK3 implement this. This will probably need to use Cairo:
-			// https://developer.gnome.org/gtk3/stable/ch26s02.html#id-1.6.3.4.5
-#if false
-			var pmap = new Gdk.Pixmap (Gdk.Screen.Default.RootWindow, size, size);
-			var gc = new Gdk.GC (pmap);
-
-			gc.RgbFgColor = new Gdk.Color (255, 255, 255);
-			pmap.DrawRectangle (gc, true, 0, 0, size, size);
-			gc.RgbFgColor = new Gdk.Color (0, 0, 0);
-			pmap.DrawRectangle (gc, false, 0, 0, (size - 1), (size - 1));
-
-			gc.SetLineAttributes (3, Gdk.LineStyle.Solid, Gdk.CapStyle.Round, Gdk.JoinStyle.Round);
-			gc.RgbFgColor = new Gdk.Color (255, 0, 0);
-			pmap.DrawLine (gc, (size / 4), (size / 4), ((size - 1) - (size / 4)), ((size - 1) - (size / 4)));
-			pmap.DrawLine (gc, ((size - 1) - (size / 4)), (size / 4), (size / 4), ((size - 1) - (size / 4)));
-
-			return Gdk.Pixbuf.FromDrawable (pmap, pmap.Colormap, 0, 0, 0, 0, size, size);
-#else
-			throw new NotImplementedException();
-#endif
+			using (var surf = new Cairo.ImageSurface(Cairo.Format.Argb32, size, size))
+			using (var g = new Cairo.Context(surf))
+            {
+				g.SetSourceColor(new Cairo.Color(1, 1, 1));
+				g.Rectangle(0, 0, size, size);
+				g.Fill();
+
+				g.SetSourceColor(new Cairo.Color(0, 0, 0));
+				g.Rectangle(0, 0, size - 1, size - 1);
+				g.Fill();
+
+				g.LineWidth = 3;
+				g.LineCap = Cairo.LineCap.Round;
+				g.LineJoin = Cairo.LineJoin.Round;
+				g.SetSourceColor(new Cairo.Color(1, 0, 0));
+				g.MoveTo(size / 4, size / 4);
+				g.LineTo((size - 1) - (size / 4), (size - 1) - (size / 4));
+				g.MoveTo((size - 1) - (size / 4), size / 4);
+				g.LineTo(size / 4, (size - 1) - (size / 4));
+
+				// TODO-GTK3 use Gdk.Pixbuf.GetFromSurface once available (https://github.com/GtkSharp/GtkSharp/issues/174)
+				return new Gdk.Pixbuf(surf.Data, true, 8, surf.Width, surf.Height, surf.Stride);
+			}
 		}
 
 		private static Gtk.IconSize GetIconSize(int size)