Use dmTransparent
draw mode for the DrawMode
property of your TBitmap32
image:
procedure TForm1.Button1Click(Sender: TObject);
var
Bitmap: TBitmap32;
Layer: TBitmapLayer;
begin
Layer := TBitmapLayer.Create(CityMap.Layers);
Bitmap := TBitmap32.Create;
Bitmap.DrawMode := dmTransparent;
Bitmap.SetSize(50, 50);
Bitmap.Canvas.Brush.Color := clYellow;
Bitmap.Canvas.Brush.Style:= bsSolid;
Bitmap.Canvas.Pen.Color := clBlue;
Bitmap.Canvas.Pen.Width := 2;
Bitmap.Canvas.Ellipse(Rect(0, 0, 50, 50));
Layer.Scaled := True;
Layer.Bitmap := Bitmap;
...
end;