WM_NCHITTEST not working in WS_EX_LAYERED form

delphi

Solution

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 :).

Problem

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. ```

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