WM_NCHITTEST not working in WS_EX_LAYERED form - delphi

Question

I'm using the code of this article http://melander.dk/articles/alphasplash/ to display a 32 bit bitmap in a form, but when i try to use a solid color bitmap instead of a image the WM_NCHITTEST message is not received and i cann't move the form. If I use 32 bitmap image the code work just fine. What i'm missing here?
This is the code
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
protected
{ Private declarations }
procedure WMNCHitTest(var Message: TWMNCHitTest); message WM_NCHITTEST;
public
{ Public declarations }
end;
var
Form1 : TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
var
BlendFunction: TBlendFunction;
BitmapPos: TPoint;
BitmapSize: TSize;
exStyle: DWORD;
Bitmap: TBitmap;
begin
// Enable window layering
exStyle := GetWindowLongA(Handle, GWL_EXSTYLE);
if (exStyle and WS_EX_LAYERED = 0) then
SetWindowLong(Handle, GWL_EXSTYLE, exStyle or WS_EX_LAYERED);
Bitmap := TBitmap.Create;
try
//Bitmap.LoadFromFile('splash.bmp'); //if I use a image the code works fine
Bitmap.PixelFormat := pf32bit;
Bitmap.SetSize(Width, Height);
Bitmap.Canvas.Brush.Color:=clRed;
Bitmap.Canvas.FillRect(Rect(0,0, Bitmap.Width, Bitmap.Height));
// Position bitmap on form
BitmapPos := Point(0, 0);
BitmapSize.cx := Bitmap.Width;
BitmapSize.cy := Bitmap.Height;
// Setup alpha blending parameters
BlendFunction.BlendOp := AC_SRC_OVER;
BlendFunction.BlendFlags := 0;
BlendFunction.SourceConstantAlpha := 255;
BlendFunction.AlphaFormat := AC_SRC_ALPHA;
UpdateLayeredWindow(Handle, 0, nil, #BitmapSize, Bitmap.Canvas.Handle,
#BitmapPos, 0, #BlendFunction, ULW_ALPHA);
Show;
finally
Bitmap.Free;
end;
end;
procedure TForm1.WMNCHitTest(var Message: TWMNCHitTest);
begin
Message.Result := HTCAPTION;
end;
end.

Answer 1

Try with:
BlendFunction.SourceConstantAlpha := 150; // 255 is fully opaque.
BlendFunction.AlphaFormat := 0;
Because your bitmap data has no source alpha. AlphaFormat for a TBitmap is by default afIgnored. 'AC_SRC_ALPHA' is only used with images having color values premultiplied with alpha. The images you are loading from the disk probably has proper alpha channel.
I can't really guess what's the relation with 'WM_NC_HITTEST' but wrong inputs yields wrong results :).