How to draw transparent text on form? - delphi

Question

Is there a way to draw a transparent text on form that has some controls? If I use TLabel control, it would always show behind controls on the form.

Answer 1

You cannot use a TLabel control, since it is not a windowed control, and therefore it will be hidden by every windowed child control of the form. You could use a TStaticText, which is indeed a windowed control (a STATIC control), but it will be a bit difficult to make it truly transparent, I'd suppose.
You can use layered windows for this:
Create a new VCL project, and add a bunch of windowed controls to it.
Create a new form in the project, named splash. Set BorderStyle to bsNone, and set the font name, size, and colour to whatever you desire (e.g., Segoe UI, 42, red).
Add a public method
procedure Tsplash.UpdateSplash(const Str: string);
var
R: TRect;
P: TPoint;
S: TPoint;
bm: TBitmap;
bf: TBlendFunction;
EXSTYLE: DWORD;
x, y: integer;
pixel: PRGBQuad;
TextRed,
TextGreen,
TextBlue: byte;
begin
EXSTYLE := GetWindowLong(Handle, GWL_EXSTYLE);
SetWindowLong(Handle, GWL_EXSTYLE, EXSTYLE or WS_EX_LAYERED);
R := ClientRect;
bm := TBitmap.Create;
try
bm.PixelFormat := pf32bit;
bm.SetSize(ClientWidth, ClientHeight);
bm.Canvas.Brush.Color := clBlack;
bm.Canvas.FillRect(ClientRect);
bm.Canvas.Font.Assign(Self.Font);
bm.Canvas.Font.Color := clWhite;
DrawText(bm.Canvas.Handle, PChar(Str), Length(Str), R,
DT_SINGLELINE or DT_VCENTER or DT_CENTER or DT_WORD_ELLIPSIS);
TextRed := GetRValue(Font.Color);
TextGreen := GetGValue(Font.Color);
TextBlue := GetBValue(Font.Color);
for y := 0 to bm.Height - 1 do
begin
pixel := bm.ScanLine[y];
x := 0;
while x < bm.Width do
begin
with pixel^ do
begin
rgbReserved := (rgbRed + rgbGreen + rgbBlue) div 3;
rgbBlue := TextBlue * rgbReserved div 255;
rgbGreen := TextGreen * rgbReserved div 255;
rgbRed := TextRed * rgbReserved div 255;
end;
inc(pixel);
inc(x);
end;
end;
P := Point(0, 0);
S := Point(bm.Width, bm.Height);
bf.BlendOp := AC_SRC_OVER;
bf.BlendFlags := 0;
bf.SourceConstantAlpha := 255;
bf.AlphaFormat := AC_SRC_ALPHA;
UpdateLayeredWindow(Handle, 0, nil, #S, bm.Canvas.Handle, #P, 0, #bf,
ULW_ALPHA)
finally
bm.Free;
end;
end;
To your main form, add private methods
procedure TForm1.CreateSplash;
var
p: TPoint;
begin
splash.Visible := true;
UpdateSplash;
end;
procedure TForm1.UpdateSplash;
var
p: TPoint;
begin
if not (Assigned(splash) and splash.Visible) then Exit;
p := ClientToScreen(Point(0, 0));
splash.SetBounds(p.X, p.Y, ClientWidth, ClientHeight);
splash.UpdateSplash('Sample Text');
end;
and call UpdateSplash every time the form is moved or resized:
procedure TForm1.WMMove(var Message: TWMMove);
begin
UpdateSplash;
end;
procedure TForm4.FormResize(Sender: TObject);
begin
UpdateSplash;
end;
Finally, you can do, just to try it out,
procedure TForm1.FormClick(Sender: TObject);
begin
if splash.Visible then
splash.Hide
else
CreateSplash;
end;
Compiled demo EXE