How to move a transparent form without border in Delphi? - delphi

Question

I already know and have used these methods to create a form without boders that can be moved.
Move form without border style
I'm using the WMNCHitTest override.
The MouseDown event don't work at all.
This form is very simple it is displaying a countdown, a number that changes very second and that's all. The number being painted using a big TLabel with big fonts.
But I also made this form transparent by using Delphi's standard form properties.
Now, if I try to click on the form to move it, the only area I can use is the lines drawing the changing numbers, even if they are not so thin, this is not practical.
I'd like the user to be able to move the numbers to any position of the screen by clicking anywhere near the numbers, let's say inside a "0" or an "8".
I'd think about drawing a transparent rectangle over the numbers and be that the clickable area, but the effect would be the same, the click would go throu.
I know an application that does this, so it is possible, but how?
procedure TfrmCountDown.Timer1Timer(Sender: TObject);
begin
iCount := iCount - 1;
lblTime.Caption := FormatFloat('00', iCount);
end;
procedure TfrmCountDown.FormCreate(Sender: TObject);
begin
iCount := 60;
BorderStyle:=bsNone;
Self.Color := clGray;
Self.TransparentColor := true;
Self.TransparentColorValue := clGray;
end;
procedure TfrmCountDown.WMNCHitTest(var Message: TWMNCHitTest);
var
Pt: TPoint;
begin
Pt := ScreenToClient(SmallPointToPoint(Message.Pos));
if Pt.Y < 160 then
Message.Result := HTCAPTION
else
inherited;
end;

Answer 1

VCL Form Transparency (by which presume you to mean the TransparentColor property, as opposed to the Alpha properties) uses Layered Windows to achieve the transparent drawing. Using this technique any transparent area of the window is not only transparent visually but also with respect to hit testing.
i.e. Using VCL form transparency, the transparent areas in your form may as well not exist at all.
What could work is to turn off the VCL form transparency and instead implement your form using the WS_EX_TRANSPARENT window style. This enables visual transparency but allows you to handle hit testing to make different areas of your form transparent, or not, with respect to clicks.
Unfortunately WS_EX_TRANSPARENT is not a complete "transparency" solution - it only tells Windows that your form is transparent, but you also then have to take additional steps to actually be properly transparent, or to interpret what "transparent" means for your specific form.
This means it complicates the visual rendering of your form and you will also have to override the paint mechanism to properly draw your form. From how you describe the content on your form this does not sound like it will be too arduous however, though it is far some straightforward (I do not have a working example unfortunately).
At the very least you will probably be best to replace your TLabel with calls to select an appropriate font and render text into the window client area with a transparent background. But there will be additional house keeping required.
In your WM_NCHITTEST handler, respond with HTNOWHERE for those areas of your form which you wish to be interpreted as "click through" areas, and HTCAPTION for the areas that you wish to support dragging (i.e. from what you describe, within a region defined by the bounds of your text).
Unfortunately I think you will find that there are lots of fiddly aspects to the implementation of painting a transparent window.