My WS_EX_TRANSPARENT window does not receive WM_PAINT after the window behind it re-paints.

Project:  SKINbedder.  Embeds other programs windows to my TWindowContainer component (CustomControl), then overlays semi-transparent PNG graphics with multiple "Hot-Spot" buttons through a TSkinLayer component(CustomControl).  (mostly used to "skin" iGuidance GPS navigation software)

Problem:  When the embedded window repaints its self, my buttons disappear.  They are not re-drawn because no WM_PAINT message gets received (even though according to MSDN, a WS_EX_TRANSPARENT window should receive a WM_PAINT whenever anything underneath it is re-drawn).  I cannot continually repaint because it ruins the semi-transparency, causes flicker, and eats CPU time.  I cannot use Rgn for a transparency effect because it wouldn't work for semi-transparency plus I want to intercept mouse clicks even on the transparent parts (no click-through).

Question:  I need a way to know when my semi-transparent buttons have been erased by the embedded window repainting its self so I can repaint my buttons.  Basically I need to 1) Intercept all WM_PAINT messages to it (although I'm not sure that would work if it is repainting due to its own internal event), 2) Assign the embedded window an OnPaint or actually a "AfterPaint" event (probably impossible), or 3) Figure out why my component doesn't always receive WM_PAINT whenever anything behind it changes (as WS_EX_TRANSPARENT controls should according to M$)

Quirk / Possible alternate solution:  If you minimize then restore my app, everything is always drawn perfectly.  I guess this is because the embedded window paints first and then I paint.  I have tried to continually repaint but also continually SendMessage(EmbeddedWindowHandle, WM_PAINT, 0, 0) first.  It didn't repaint its self over my buttons though so that did not solve the ruining semi-transparency bug as I had hoped.

Source Code:  Below is the source code to my TSkinLayer.  Any suggestions about any part of the component are welcome ;).  This and TWindowContainer are my first 2 components ever (and are based on TmodderBut which was posted here on experts-exchange for an earlier version of this same program).


[code]

unit SkinLayer;

interface

uses
//  Dialogs,
  Windows, Messages, Classes, Graphics, Controls, Forms, PNGImage;

type
  THotSpots = record
    Top: integer;
    Bottom: integer;
    Left: integer;
    Right: integer;
    OnPressDown: String;
    OnPressUp: String;
    Toggle: Boolean;
   end;

  TSkinLayer = class(TCustomControl)
   private
   protected
    FNorm, FDown: TPNGObject;
    FHotSpots: Array of THotSpots;
    procedure WMEraseBkgnd(var Msg: TWMEraseBkgnd); message WM_ERASEBKGND;
    procedure CreateParams(var Params: TCreateParams); override;
    procedure Paint; override;
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
    procedure MouseUp(Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
   public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    procedure WriteHotSpot(Index: integer; Top, Bottom, Left, Right: integer; OnPressUp, OnPressDown: String);
    function ReadHotSpot(Index: integer; var Top: Integer; var Bottom: Integer; var Left: Integer; var Right: integer; var OnPressUp: String; var OnPressDown: String): Boolean;
    property Canvas;
   published
    property NormalBmp: TPNGObject read FNorm write FNorm;
    property DownBmp: TPNGObject read FDown write FDown;
    property Height default 1;
    property Width default 1;
    property Visible default False;
    property Cursor default crCross;
    property Name;
    property Anchors;
    property Left;
    property Top;
    property OnMouseDown;
    property OnMouseUp;
   end;

procedure Register;

implementation

uses
  SysUtils;

procedure Register;
 begin
  RegisterComponents('RPM', [TSkinLayer]);
 end;

//--- WMEraseBkgnd -----------------------------------------------------------\\
procedure TSkinLayer.WMEraseBkgnd(var Msg: TWMEraseBkgnd);
 begin
  Msg.Result := 1;
 end;
//--- End WMEraseBkgnd -------------------------------------------------------//

//--- CreateParams -----------------------------------------------------------\\
procedure TSkinLayer.CreateParams(var Params: TCreateParams);
 begin
  inherited CreateParams(Params);
  with Params do
   begin
    WindowClass.lpszClassName := 'TSkinLayer';
    WindowClass.hbrBackground := 0;
    WindowClass.style := WindowClass.style OR CS_HREDRAW OR CS_VREDRAW OR CS_OWNDC OR CS_SAVEBITS;
    Style := Style OR WS_CHILD OR WS_CLIPSIBLINGS AND NOT(WS_TABSTOP) AND NOT(WS_VISIBLE);
    ExStyle := ExStyle OR WS_EX_TRANSPARENT;
   end;
 end;
//--- End CreateParams -------------------------------------------------------//

//--- Create -----------------------------------------------------------------\\
constructor TSkinLayer.Create(AOwner: TComponent);
 begin
  inherited Create(AOwner);
  ControlStyle := [csCaptureMouse, csClickEvents, csFixedWidth, csFixedHeight, csReflector];
  Width := 1;
  Height := 1;
  Cursor := crCross;
  Visible := False;
  FNorm := TPNGObject.Create;
  FDown := TPNGObject.Create;
 end;
//--- End Create -------------------------------------------------------------//

//--- Destroy ----------------------------------------------------------------\\
destructor TSkinLayer.Destroy;
 begin
  FreeAndNil(FNorm);
  FreeAndNil(FDown);
  inherited Destroy;
 end;
//--- End Destroy ------------------------------------------------------------//

//--- WriteHotSpot -----------------------------------------------------------\\
procedure TSkinLayer.WriteHotSpot(Index: integer; Top, Bottom, Left, Right: integer; OnPressUp, OnPressDown: String);
 begin
  if (length(FHotSpots) < (Index + 1)) then
    SetLength(FHotSpots, Index + 1);
  FHotSpots[Index].Top := Top;
  FHotSpots[Index].Bottom := Bottom;
  FHotSpots[Index].Left := Left;
  FHotSpots[Index].Right := Right;
  FHotSpots[Index].OnPressUp := OnPressUp;
  FHotSpots[Index].OnPressDown := OnPressDown;
  FHotSpots[Index].Toggle := False;
 end;
//--- End WriteHotSpot -------------------------------------------------------//

//--- ReadHotSpot ------------------------------------------------------------\\
function TSkinLayer.ReadHotSpot(Index: integer; var Top: Integer; var Bottom: Integer; var Left: Integer; var Right: integer; var OnPressUp: String; var OnPressDown: String): Boolean;
 begin
  if Index < length(FHotSpots) then
   begin
    Top := FHotSpots[Index].Top;
    Bottom := FHotSpots[Index].Bottom;
    Left := FHotSpots[Index].Left;
    Right := FHotSpots[Index].Right;
    OnPressUp := FHotSpots[Index].OnPressUp;
    OnPressDown := FHotSpots[Index].OnPressDown;
    Result := True;
   end
  else
    Result := False;
 end;
//--- End ReadHotSpot --------------------------------------------------------//

//--- Paint ------------------------------------------------------------------\\
procedure TSkinLayer.Paint;
var
  Index: Integer;
 begin
  Parent.Update;  //Reduces re-draw errors while draging a window in front of us.

  //Draw FNorm and then overlay FDown if button is Toggled (bad method!)
  if not(FNorm.Empty) then
   begin
    FNorm.Draw(Canvas, Rect(0, 0, FNorm.Width, FNorm.Height));
    if not(FDown.Empty) then
     begin
      Index := 0;
      while (Index < length(FHotSpots)) do
       begin
        if (FHotSpots[Index].Toggle) then
          FDown.Draw(Canvas, Rect(FHotSpots[Index].Left, FHotSpots[Index].Top, FHotSpots[Index].Right, FHotSpots[Index].Bottom));
        Index := Index + 1;
       end;
     end;
   end;
 end;
//--- End Paint --------------------------------------------------------------//

//--- MouseDown --------------------------------------------------------------\\
procedure TSkinLayer.MouseDown(Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
var
  Index: Integer;
 begin
  Index := 0;
  while (Index < length(FHotSpots)) do
   begin
    if (X > FHotSpots[Index].Left) and (X < FHotSpots[Index].Right) and (Y > FHotSpots[Index].Top) and (Y < FHotSpots[Index].Bottom) then
     begin
      if (FHotSpots[Index].OnPressDown = '') then
       begin
        //No Down Command: Just paint FDown to HotSpot.
        if (not FDown.Empty) then
          FDown.Draw(Canvas, Rect(FHotSpots[Index].Left, FHotSpots[Index].Top, FHotSpots[Index].Right, FHotSpots[Index].Bottom));
       end
      else if not(FHotSpots[Index].Toggle) then
       begin
        //Non-Toggle or 1st-Click: Run command & paint FDown to HotSpot.
        inherited;  //Command is run in external OnMouseDown Event (assigned in MainForm on create)
        if (not FDown.Empty) then
          FDown.Draw(Canvas, Rect(FHotSpots[Index].Left, FHotSpots[Index].Top, FHotSpots[Index].Right, FHotSpots[Index].Bottom));
        //If Toggle, set flag.
        if (FHotSpots[Index].OnPressUp <> '') then
          FHotSpots[Index].Toggle := True;
       end
      else
        //Toggle-Button 2nd-Click: Do nothing, but handle next up.
        FHotSpots[Index].Toggle := False;
     end;
    Index := Index + 1;
   end;
 end;
//--- End MouseDown ----------------------------------------------------------//

//--- MouseUp ----------------------------------------------------------------\\
procedure TSkinLayer.MouseUp(Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
var
  Index: Integer;
 begin
  Index := 0;
  while (Index < length(FHotSpots)) do
   begin
    if (X > FHotSpots[Index].Left) and (X < FHotSpots[Index].Right) and (Y > FHotSpots[Index].Top) and (Y < FHotSpots[Index].Bottom) then
     begin
      if (FHotSpots[Index].OnPressUp = '') then
       begin
        //No Up Command: Just paint FNorm to HotSpot.
        if not(FNorm.Empty) then
          FNorm.Draw(Canvas, Rect(FHotSpots[Index].Left, FHotSpots[Index].Top, FHotSpots[Index].Right, FHotSpots[Index].Bottom));
       end
      else if not(FHotSpots[Index].Toggle) then
       begin
        //Non-Toggle or 2nd-Click: Run Command and paint FNorm to HotSpot
        inherited;  //Command is run in external OnMouseDown Event (assigned in MainForm on create)
        if not(FNorm.Empty) then
          FNorm.Draw(Canvas, Rect(FHotSpots[Index].Left, FHotSpots[Index].Top, FHotSpots[Index].Right, FHotSpots[Index].Bottom));
       end;
        //If 1st-Click on Toggle-Button, do nothing.
     end;
    Index := Index + 1;
   end;
 end;
//--- End MouseUp ------------------------------------------------------------//

end.

[/code]