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[Solved] Lazarus Pascal - Determine titlebar height crossplatform quick and easy

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Joined: 11 years ago
Posts: 2677
Topic starter  

Seems hard to determine the height of the titlebar/caption of a form.
I've seen some calls that are Windows specific only, and some tricks that maximize the form to determine the size (flicker), or system calls that simply do not work on all platforms.

So after tinkering with that issue for a bit, I figured; why not use the "translation" of a pixel on a form to its location on the screen and determine how much it's off? (a.k.a. the titlebar height)

Tested this under Windows (11), macOS (Monterey and Sonoma), GTK2 and QT5 ... and it just works ...

function DetermineTitlebarHeight(aForm:Tform):integer;
  global_pos : TPoint;
  global_pos := aForm.ClientToScreen(Point (1,1));
  Result     := global_pos.Y - aForm.Top;

I've tested this at onFormPaint and onFormChangeBounds, and even when changing themes (Linux) it adapts.

For testing I've added a little project that has 2 units, where the 2nd unit stays aligned to the bottom of the first unit.