Author: Tomas Rutkauskas

I try to determine if the mouse is just over a tab of a TTabControl using 
GetHitTestInfoAt(). This returns htOnItem if the mouse is over the tab and if it's 
not. How do I have to approach this issue?

Answer:

Probably, the problem is in the routine which calls GetHitTestInfoAt, since I've 
tried to check this method and all seemed to work fine. I was calling it in the 
form's and tabcontrols's OnMouseMove events:
1   
2   procedure TForm1.TabControl1MouseMove(Sender: TObject; Shift: TShiftState; X, Y:
3     Integer);
4   var
5     XHitTests: THitTests;
6   begin
7     XHitTests := TabControl1.GetHitTestInfoAt(X, Y);
8     if htOnItem in XHitTests then
9       ShowMessage('OnItem');
10  end;


Also, you can try to call Win API macro TabCtrl_HitTest directly, in order to 
determine which tab, if any, is over the cursor. Here's an example:
11  
12  procedure TForm1.TabControl1MouseMove(Sender: TObject; Shift: TShiftState; X, Y:
13    Integer);
14  var
15    XHitTestInfo: TTCHitTestInfo;
16    XIndex: integer;
17  begin
18    XHitTestInfo.pt := POINT(X, Y);
19    XIndex := TabCtrl_HitTest(TabControl1.Handle, @XHitTestInfo);
20    if XHitTestInfo.flags in [TCHT_ONITEM] then
21      ShowMessage('OnItem ' + TabControl1.Tabs[XIndex])
22    else if XHitTestInfo.flags in [TCHT_ONITEMICON] then
23      ShowMessage('OnIcon ' + TabControl1.Tabs[XIndex])
24    else if XHitTestInfo.flags in [TCHT_ONITEMLABEL] then
25      ShowMessage('OnLabel ' + TabControl1.Tabs[XIndex]);
26  end;