Here are the API changes that occured between GtkAda 1.2 and GtkAda 2.0:

Glib:
  GType_* constants replace Gtk.Gtk_Type_*
Glib.Error:
  new package related to error handling
Glib.Convert:
  new package related to strings conversion to utf8
Glib.GObjects: new package
Glib.Properties.Creation:
  Gnew_Closure: removed.
Gdk.Color_Context: removed, use Gdk.Color instead.
Gdk.Color:
  Get_System: removed, replace with Gtk.Widget.Get_Default_Colormap
  Get_System_Size: removed
Gtk.Combo:
  Get_Popup_Window: new procedure.
  Set_Value_In_List: Val is now a Boolean.
Gdk.Cursor:
  Destroy: deprecated, use Unref instead.
  Ref/Unref: new procedures.
Gdk.Drawable:
  Get_Type, Get_Size: new functions.
  Get_Size, Set/Get_Colormap, Get_Visual: moved from Gdk.Window.
  Draw_Pixmap, Copy_Area: removed, use Draw_Drawable.
  Get_Depth, Ref, Unref: new procedures.
Gdk.Event:
  Gdk_Event_Scroll: new type.
  Get_Pressure, Get_Xtilt, Get_Ytilt, Get_Source: removed
  Get_Type: replace Gtk.Gtk_Type_Gdk_Event
  Get_Event: replace Gtk.Arguments.To_Event
Gdk.Font:
  Text_*: Removed, use String_* instead.
Gdk.Gc:
  Destroy: deprecated, use Unref instead.
  Set_Values: new procedure.
Gdk.Image:
  Destroy: deprecated, use Unref instead.
  Ref/Unref: new procedures.
Gdk.Main:
  Time_Get: removed.
  Timer_Get/Set/Enable/Disable: removed.
  Key_Repeat/Disable: removed.
  Set_Double_Click_Time: new procedure.
Gdk.Pixbuf:
  now part of libgtkada
  upgrade to gdk pixbuf 0.8, now part of Gtk+
  rendering functions have been suppressed.
  see gdk-pixbuf.ads for the complete list of new functions.
  Get_Frames, Copy (Gdk_Pixbuf_Animation): Removed.
  Gdk_New_From_Inline : Removed.
Gdk.Pixmap:
  Destroy: deprecated, use Unref instead.
Gdk.Rectangle:
  Gdk_Rectangle now takes gint instead of gint16 and guint16.
  GRectangle_Coord, GRectangle_Length: New subtypes provided for better compat.
Gdk.Region:
  Union_With_Rect, Intersect, Union, Substract, Gdk_Xor: Profile changed,
    Source1 is now in out (both source and result).
  Copy, Rectangle, Get_Rectangles: new functions.
Gdk.Rgb:
  Init: removed, not longer needed.
  Gtk_New: renamed Gdk_New.
  Get_8, Set_8: removed
Gdk.Types:
  Gdk_Point, Gdk_Segment: fields are now Gint instead of Gint16.
Gdk.Visual:
  Get_Best_Depth, Get_Best_Type, Get_System, Get_Best: now functions.
Gdk.Window:
  Get_Type: renamed Get_Window_Type.
  Focus, Scroll, Shape_Combine_Mask/Region,
  Get_State, Set_Static_Gravities, Set_Type_Hint, Set_Modal_Hint,
  Get_Frame_Extents, Iconify, Deiconify, Stick, Unstick,
  Maximize, Unmaximize, Register_Dnd, Get_Update_Area,
  Freeze/thaw_Updates, Process_All_Updates, Process_Updates,
  Set_Debug_Updates : new procedures.
  Copy_Area: obsolete. use Gdk.Drawable.Draw_Drawable instead.
  Get_Size, Set/Get_Colormap, Get_Visual: moved to Gdk.Drawable.
Gtk:
  Gtk_Type_* constants replaced by Glib.GType_*
  Gtk_Type_Gdk_Event: replace by Gdk.Event.Get_Type
  Root_Type replaced by Glib.GObjects.GObject_Record
  All subprograms related to Root_Type moved to Glib.GObjects as well.
Gtk.Accel_Group:
  Major changes in API, see gtk-accep_group.ads
Gtk.Adjustments:
  all Gfloat replaced by Gdouble
Gtk.Arguments obsolete, use Glib.Values instead
Gtk.Box:
  New function Get_Spacing
Gtk.Button:
  New procedures Gtk_New_From_Stock, Gtk_New_From_Mnemonic
Gtk.Button_Box:
  Set/Get_Spacing: removed since redundant with Gtk.Box
  Set/Get_Child*: removed
Gtk.Calendar:
  New signals: "day_selected", "day_selected_double_click",
   "prev_month", "next_month", "prev_year", "next_year"
Gtk.Check_Button:
  Gtk_New/Initialize: With_Label renamed Label.
  new procedure: Gtk_New_With_Mnemonic
Gtk.Check_Menu_Item:
  Set_Show_Toggle, Set_Always_Show_Toggle: removed (deprecated).
  new procedures: Set_Inconsistent, Get_Inconsistent.
Gtk.Clist: deprecated, use Gtk_Tree_View instead.
Gtk.Color_Selection:
  new functions Set/Get_Use_Opacity, Get/Set_Has_Opacity_Control,
   Get/Set_Has_Palette, Get/Set_Current_Color, Get/Set_Current_Alpha,
   Set/Get_Previous_Color, Get/Set_Previous_Alpha, Palette_From_String,
   Palette_To_String, Set_Change_Palette_Hook.
  Set_Opacity, Get/Set_Use_Opacity, Get/Set_Use_Palette: removed
Gtk.Color_Selection_Dialog:
  now a child of Gtk_Dialog.
  Get_Reset_Button: removed
Gtk.Container:
  Get_Toplevels, Register_Toplevel, Unregister_Toplevel: removed, use
   Gtk.Window.List_Toplevels instead.
  new functions: Propagate_Expose, Set/Unset_Focus_Chain, Resize_Children.
  Focus: Removed.
  Children: replace by Get_Children
  Set_Border_Width: now takes a Guint instead of a Gint.
  Get_Border_Width, Get_Resize_Mode: new functions.
Gtk.Ctree: deprecated, use Gtk_Tree_View instead.
Gtk.Curve: type Gtk_Curve_Type moved to Gtk.Enums.
Gtk.Data: removed, obsolete.
Gtk.Editable:
  The old Gtk.Editable has been renamed Gtk.Old_Editable and is obsolete.
  Gtk.Editable is a new package providing an abstract interface for text edition
Gtk.Enums:
  Gtk_Scroll_Type has new values
  Gtk_Window_Position has a new value
  The Window_Dialog value has been removed from Gtk_Window_Type
  Gtk_Scroll_Type has new values.
  New type Gtk_Text_Direction, Gtk_Anchor_Type, Gtk_Side_Type, Gtk_Wrap_Mode
  Gtk_Trough_Type: removed.
  Selection_Extended: removed, use Selection_Multiple instead.
  Gtk_Scroll_Type: Scroll_Page_Start/End renamed Scroll_Start/End
Gtk.Extra.PsFont: Removed, replaced by Pango.Font
Gtk.File_Selection:
  now a child of Gtk_Dialog
Gtk.Fixed:
  new procedure: Set_Has_Window
  Move, Put: now take Gint instead of Gint16 as parameters.
Gtk.Font_Selection:
  Gtk_Font_Selection_Dialog is now a child of Gtk_Dialog
  Gtk_Font_Selection is now a child of Gtk_Vbox
  Font_Metric_Type, Font_Type, Font_Filter_Type: removed.
  Set_Filter: removed
Gtk.Frame:
  new functions Get_Label, Set_Label_Widget.
Gtk.Gentry
  now a child of Gtk_Widget.
  new signals:
    "insert_text"
    "delete_text"
    "changed"
    "populate_popup"
    "activate"
    "move_cursor"
    "insert_at_cursor"
    "delete_from_cursor"
    "cut_clipboard"
    "copy_clipboard"
    "paste_clipboard"
    "toggle_overwrite"
  Select_Region: removed.

Gtk.Grange:
  Draw_*, Default_*, Slider_Update, Trough_Click: removed since internal
  Set/Get_Inverted: new functions
Gtk.Handlers:
  Use Glib.Values instead of Gtk.Arguments.
  Relatively good compatibility kept however.
Gtk.Image:
  Gtk_Image_Type: new type.
  Get_Storage_Type,
  Get/Set from Pixmap, File, Pixbuf, Stock, Icon_Set: new functions.
  Gtk_New (From_Animation), Get/Set (From_Animation): new functions.
Gtk.Invisible:
  now a child of Gtk.Widget.
Gtk.Item_Factory:
  Parse_Rc, Parse_Rc_String, Print_Func: removed.
Gtk.Label:
  Get: deprecated. use Get_Text instead.
  Parse_Uline: removed (replaced by Gtk_New_With_Mnemonic).
Gtk.Layout:
  Freeze, Thaw: now empty since no longer needed.
  Get_Width, Get_Height : deprecated
  Get_Size: new function
Gtk.List: deprecated, use Gtk_Tree_View instead.
Gtk.Marshallers:
  Use Glib.Values instead of Gtk.Arguments.
Gtk.Menu:
  Append, Insert, Prepend: removed since redundant with Gtk.Menu_Shell
  Ensure_Uline_Accel_Group, Get_Uline_Accel_Group: removed
Gtk.Menu_Bar:
  Set_Shadow_Type: removed.
  Append : removed.
  Insert : removed.
  Prepend : removed.
Gtk.Menu_Item:
  Gtk_New_With_Mnemonic: new function.
  Configure, Set_Placement : removed.
Gtk.Men_Shell:
  Gtk_Menu_Direction_Type: moved to Gtk.Enums.
Gtk.Notebook:
  Get_Notebook_Page: replace Gtk.Arguments.To_Notebook_Page
  Get_Cur_Page, Get_Tab_Label, Get_Allocation_*, Get_Child: removed
  Get_Menu_Label: spec modified to take a notebook+widget instead of a
    Gtk_Notebook_Page
  Set_Page : replace by Set_Current_Page
Gtk.Option_Menu:
  Get_History: new function.
Gtk.Packer: deprecated, removed.
Gtk.Paned:
  Set/Get_Gutter_Size: stubs provided for compatibility only.
  Set/Get_Handle_Size: stubs provided for compatibility only.
  Get_Position: new function.
Gtk.Pixmap: deprecated, use Gtk.Image instead.
  Get_Mask, Get_Pixmap: Removed, see Get instead
Gtk.Preview: deprecated.
Gtk.Progress: deprecated.
  All functions but Set_Text_Alignment now take Gdouble instead of Gfloat.
Gtk.Progress_Bar: major API changes, see spec. Previous API wasn't usable.
Gtk.Radio_Button:
  New/Initialize_With_Mnemonic: new functions
  Group : replace by Get_Group.
Gtk.Radio_Menu_Item:
  New/Initialize_With_Mnemonic: new functions
  Group : replace by Get_Group.
Gtk.Range:
  Set_Increments, Set_Range, Get/Set_Value: new subprograms.
Gtk.Rc:
  Now completely bound. See gtk-rc.ads for more details.
Gtk.Ruler:
  all functions now take/return Gdouble instead of Gfloat.
  Get_Lower, Get_Upper, Get_Max_Size, Get_Position : removed
  Get_Range, Get_Metric : new functions
Gtk.Scale:
  Gtk_New_Hscale, Get_Value_Size, Get_Digits, Get_Draw_Value,
   Get_Value_Pos: new functions.
  Draw_Value, Get_Value_Size, Get_Value_Width: removed.
Gtk.Scrolled_Window:
  now a child of Gtk_Bin (instead of Gtk_Container).
  Set_Shadow_Type: new function.
  Gtk_Corner_Type: moved to Gtk.Enums.
Gtk.Selection:
  Clear_Targets: new function.
Gtk.Settings: new package.
Gtk.Signal: removed, obsolete. Use Gtk.Handlers instead.
Gtk.Spin_Button:
  type Gtk_Spin_Button_Update_Policy moved here (from Gtk.Enums).
  Gfloat parameters replaced by Gdouble.
  Spin: now takes a Gtk_Spin_Type and a Gdouble as parameters.
  Set_Digits: now takes a Guint instead of a Gint.
  Gtk_New (with range), Set_Increments, Set_Range, Update: new procedures.
  Get_Value_As_Float: removed, use Get_Value instead.
Gtk.Status_Bar:
  Set/Get_Has_Resize_Grip: new functions.
Gtk.Style:
  significant additions. see spec for details.
  Draw_String: deprecated.
  Draw_Oval: removed.
  Set_Font, Get_Font: deprecated
  Set_Font_Description, Get_Font_Description: new functions
Gtk.Text_Buffer: new package.
Gtk.Text_Child: new package.
Gtk.Text_Iter: new package.
Gtk.Text_Mark: new package.
Gtk.Text_Tag: new package.
Gtk.Text_Tag_Table: new package.
Gtk.Text_View: new package.
Gtk.Tips_Query: deprecated.
Gtk.Toggle_Button:
  New_With_Mnemonic, Set/Get_Inconsistent: new functions.
  Is_Active: removed, was deprecated. Use Get_Active instead.
Gtk.Toolbar:
  Gtk_New, Initialize: function profile modified.
  Remove_Space, Set/Unset_Icon_Size, Insert_Stock, Unset_Style : new functions.
  Set_Space_Size, Set_Space_Style, Get/Set_Button_Relief: removed.
Gtk.Tooltips:
  now a child of Gtk_Object.
  Set_Colors: removed, was deprecated. The colors for tooltips are now taken
   from the style.
Gtk.Tree: removed, deprecated, use Gtk_Tree_View instead.
Gtk.Tree_Item: removed, deprecated, use Gtk_Tree_View instead.
Gtk.Vbutton_Box:
  Get/Set_Spacing_Default: removed, deprecated, noop.
  Get/Set_Layout_Default: removed, deprecated, noop.
Gtk.Widget:
  Accelerator_Signal, Lock_Accelerators, Remove_Accelerators,
   Unlock_accelerators: removed.
  Gtk_Requisition, Gtk_Allocation: now takes gint insstead of gint16.
  Double_Buffered_Is_Set, Set_Double_Buffered,
  Get_Parent_Window, Hide_On_Delete, Get_Modifer_Style: new function.
  Set_Default_Visual, Push/Pop_Visual, Get_Visual, Set_Rc_Style: removed
  Draw_Default, Draw_Focus, Popup: removed
  Set_USize: deprecated
  Set_Size_Request: new function
  Modify_Style, Get_Modifier_Style: moved to Gtk.Rc
Gtk.Window:
  Set_Role, Set_Destroy_With_Parent,
  Set/Get_Resizable, Set_Has_Frame, Set_Frame_Dimensions,
  Set_Decorated, List_Toplevels, Present,
  Iconify, Deiconify, Stick, Unstick,
  Maximize, Unmaximize: new procedures.
  Set_Policy, Set_Default_Size: deprecated.
  Get_Transient_Parent: renamed Get_Transient_For