Theming & code duplication

[Frank Richter]

Hi,
somewhat recently I sent some code to wine-patches to add button
theming; if you have glanced at it, despite utilizing subclassing, code
was duplicated from the button code in user.

In particular, the themed button does its own state management. The
reason is that upon state changes, the user32 button control does some
repaints internally, ie calling the paint function directly - those
can't obviously be hooked by subclassing alone. In early versions I had
the themed button painted over after state-changing messages, but that
causes visible flickering (since the button is first painted in
"classic" style and the themed style is painted above that).

The basic problem - painting that is hard to hook into - will probably
also arise on other controls.

There are some ideas and approaches to deal with the problem that came
up (and the results from discussion with Kevin):
- Ignore. Have ugly flickering.
- Change the classic controls to use InvalidateRect() instead when
internal painting functions are called, so painting messages can be
hooked. That would deviate from native behaviour, though (and also
occasionally less efficient when the control just paints some change).
- Use some magic message the control sends to itself to do some painting
which is then hooked. Makes things more complex, could cause
compatibility issues with apps that may not handle this message and is
incompatible with native.
- Code duplication - e.g. in the case of buttons, do state management in
the themed class as well.
- Static libraries - implement the standard controls in a static library
and allow for hooks to override painting (in C++ you'd use virtual
methods). Both user32 and comctl32 would link against that lib, and the
latter would provide alternative painting functions. Binarily equivalent
to code duplication, but not that bad in the source code. For me it
looks like a good compromise, though, Kevin noted that "Historically
static libs have not gone over very well".

I don't like the current code duplication for theming that much, but I'm
a bit unsure what else could be done. Perhaps you have some comments or
suggestions, and hopefully there will be some consent of what approach
would be best for Wine.

Thanks for reading,
-f.r.

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