[GTK3] Revert to manually scaling the surface, cairo_surface_set_device_scale is not supported on Ubuntu 14.04

src/Gtk/Avalonia.Gtk3/ImageSurfaceFramebuffer.cs

@@ -32,21 +32,23 @@ namespace Avalonia.Gtk3
             Height = height;
             Address = Native.CairoImageSurfaceGetData(_surface);
             RowBytes = Native.CairoImageSurfaceGetStride(_surface);
-            Native.CairoSurfaceSetDeviceScale(_surface, factor, factor);
             Native.CairoSurfaceFlush(_surface);
         }
 
-        static void Draw(IntPtr context, CairoSurface surface)
+        static void Draw(IntPtr context, CairoSurface surface, double factor)
         {
+            
             Native.CairoSurfaceMarkDirty(surface);
+            Native.CairoScale(context, 1d / factor, 1d / factor);
             Native.CairoSetSourceSurface(context, surface, 0, 0);
             Native.CairoPaint(context);
+
         }
         /*
         static Stopwatch St =Stopwatch.StartNew();
         private static int _frames;
         private static int _fps;*/
-        static void DrawToWidget(GtkWidget widget, CairoSurface surface, int width, int height)
+        static void DrawToWidget(GtkWidget widget, CairoSurface surface, int width, int height, double factor)
         {
             if(surface == null || widget.IsClosed)
                 return;
@@ -56,7 +58,7 @@ namespace Avalonia.Gtk3
             var rc = new GdkRectangle {Width = width, Height = height};
             Native.GdkWindowBeginPaintRect(window, ref rc);
             var context = Native.GdkCairoCreate(window);
-            Draw(context, surface);
+            Draw(context, surface, factor);
             /*
             _frames++;
             var el = St.Elapsed;
@@ -82,13 +84,15 @@ namespace Avalonia.Gtk3
         {
             private readonly GtkWidget _widget;
             private CairoSurface _surface;
+            private readonly double _factor;
             private readonly int _width;
             private readonly int _height;
 
-            public RenderOp(GtkWidget widget, CairoSurface _surface, int width, int height)
+            public RenderOp(GtkWidget widget, CairoSurface _surface, double factor, int width, int height)
             {
                 _widget = widget;
                 this._surface = _surface;
+                _factor = factor;
                 _width = width;
                 _height = height;
             }
@@ -101,7 +105,7 @@ namespace Avalonia.Gtk3
 
             public void RenderNow()
             {
-                DrawToWidget(_widget, _surface, _width, _height);
+                DrawToWidget(_widget, _surface, _width, _height, _factor);
             }
         }
         
@@ -112,13 +116,13 @@ namespace Avalonia.Gtk3
                 if (Dispatcher.UIThread.CheckAccess())
                 {
                     if (_impl.CurrentCairoContext != IntPtr.Zero)
-                        Draw(_impl.CurrentCairoContext, _surface);
+                        Draw(_impl.CurrentCairoContext, _surface, _factor);
                     else
-                        DrawToWidget(_widget, _surface, Width, Height);
+                        DrawToWidget(_widget, _surface, Width, Height, _factor);
                     _surface.Dispose();
                 }
                 else
-                    _impl.SetNextRenderOperation(new RenderOp(_widget, _surface, Width, Height));
+                    _impl.SetNextRenderOperation(new RenderOp(_widget, _surface, _factor, Width, Height));
                 _surface = null;
             }
         }

src/Gtk/Avalonia.Gtk3/Interop/Native.cs

@@ -179,9 +179,6 @@ namespace Avalonia.Gtk3.Interop
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Cairo)]
             public delegate void cairo_surface_destroy(IntPtr surface);
             
-            [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Cairo)]
-            public delegate void cairo_surface_set_device_scale(CairoSurface surface, double sx, double sy);
-            
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Cairo)]
             public delegate void cairo_set_source_surface(IntPtr cr, CairoSurface surface, double x, double y);
             
@@ -468,7 +465,6 @@ namespace Avalonia.Gtk3.Interop
         public static D.cairo_surface_write_to_png CairoSurfaceWriteToPng;
         public static D.cairo_surface_flush CairoSurfaceFlush;
         public static D.cairo_surface_destroy CairoSurfaceDestroy;
-        public static D.cairo_surface_set_device_scale CairoSurfaceSetDeviceScale;
         public static D.cairo_set_source_surface CairoSetSourceSurface;
         public static D.cairo_set_source_rgba CairoSetSourceRgba;
         public static D.cairo_scale CairoScale;