How to load a transparent Image from ImageList?

问题

I want to load a picture (32 bit-depth, transparent) from a TImageList to an TImage. The standard approach would be ImageList.GetBitmap(Index, Image.Picture.Bitmap);. However the GetBitmap method doesn't work with transparency, so I always get a non-transparent bitmap.

回答1:

The workaround is rather simple - ImageList offers another method, GetIcon, which works OK with transparency. Code to load a transparent Image would be:

ImageList.GetIcon(Index, Image.Picture.Icon);

And don't forget to set proper ImageList properties:

ImageList.ColorDepth:=cd32bit;
ImageList.DrawingStyle:=dsTransparent;

回答2:

I too have had various issues with passing in images from the a tImageList. So I have a simple wrapper routine that generally does the job and it enforces the transparency. The code below is Delphi 2005 and imlActiveView is the tImageList component that has my set of button glyph images.

procedure TfrmForm.LoadBitmap (Number : integer; bmp : tBitMap);
var
  ActiveBitmap : TBitMap;
begin
  ActiveBitmap := TBitMap.Create;
  try
    imlActiveView.GetBitmap (Number, ActiveBitmap);
    bmp.Transparent := true;
    bmp.Height      := ActiveBitmap.Height;
    bmp.Width       := ActiveBitmap.Width;
    bmp.Canvas.Draw (0, 0, ActiveBitmap);
  finally
    ActiveBitmap.Free;
  end
end;

Here is an example of use where the 5th imlActiveView image is passed into the btnNavigate.Glyph.