#113 TWindow::SetWindowFont overload for TFont

[Vidar Hasfjord]

As discussed in the forum topic "TFontText" [discussion:214f1787], it would be nice to have a simple way to set the font for a control. OWLNext currently requires that the parent (dialog) manages the lifetime of the font, which requires additional class members (e.g. TFont objects). What we need is the ability to pass a TFont to TWindow::SetWindowFont and forget about it.

[Vidar Hasfjord]

This feature was implemented in Owlet in [r3731] and merged into the trunk in [r3739]. A new example, "examples/classes/static", was added in [r3744] to demonstrate the new feature.

Note that a TFont object can be an owner or a non-owner of the underlying font handle. A copy of a TFont object does not create a new font. Both objects will share the underlying handle, and reference-counting is used to ensure that the handle is deleted when the last owner is destructed.

The solution exploits these semantics. If a TFont is created as a temporary object at the point of call to SetWindowFont, the TFont copy constructor will share the handle with the callee. The reference count will be 2, then decremented to 1 as the temporary object is destructed after the call. The result is that the callee is now the owner of the font.

However, note that a TFont can be a non-owner as well. In this case, there is no ownership transfer in the call, and the caller is responsible for ensuring that the font handle outlives the window:

:::C++
Label1.SetWindowFont(TFont{"Arial", -9}); // Font handle ownership transfer.
Label1.SetWindowFont({"Arial", -9}); // Same as above; TFont is inferred.

TFont f{GetWindowFont()}; // Aliasing; f does not own the handle.
Label2.SetWindowFont(f); // No font handle ownership transfer.
Label2.SetWindowFont(f.GetHandle()); // Equivalent to above.

Please review.

[Vidar Hasfjord]

A regression, causing a crash while dispatching WM_SETFONT for a premature window, was fixed in [r4177], and the fix was merged into Owlet in [r4178].

See https://sourceforge.net/p/owlnext/discussion/97177/thread/071b2a02/#f2d6

[Vidar Hasfjord]

Unfortunately the fix implemented in [r4177] for the crash in the dispatch of WM_SETFONT causes a regression.

See [bugs:#507] "Font change in SetupWindow is ignored (regression in 7.0)".