wxWidgets/docs/contributing/wxmsw-contributor-guide.md

Special notes about writing wxMSW code

0. Purpose

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This is just a collection of various notes which should be useful to anybody working on wxMSW codebase, please feel free to add more here.

This text assumes familiarity with both Windows programming and wxWidgets so it doesn't cover any wxWidgets-wide issues not specific to Windows.

1. Windows headers wrappers

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In no event should the Windows headers such as <windows.h> or <commctrl.h> be included directly. So instead of #include <...> use "wx/msw/wrapwin.h" or wx/msw/wrapcctl.h.

For convenience it is also possible to replace #include <commdlg.h> and <shlobj.h> with #include "wx/msw/wrapcdlg.h" and wrapshl.h but this is less vital.

Also notice that many convenient (albeit undocumented) functions and classes are declared in "wx/msw/private.h", please do become familiar with this file contents and use the utility classes and functions from it instead of duplicating their functionality (which can often be done only in exception unsafe way).

2. Utility classes

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wxWidgets provides a couple of useful (mostly undocumented) classes making Windows API easier to work with.

Please whenever possible do not use raw pointers for BSTR, COM interfaces or task memory, use the appropriate RAII wrapper instead (see below).

Grep wxWidgets source code for the class name to see how it is to be used.

wxBasicString: for BSTR, in "wx/msw/ole/oleutils.h"

wxCOMPtr: simplistic smart pointer for COM interfaces, in "wx/msw/private/comptr.h"

wxCoTaskMemPtr: smart pointer for memory allocated/freed with CoTaskMem{Alloc/Free}(), in "wx/msw/private/cotaskmemptr.h"

wxSafeArray: for SAFEARRAY, in "wx/msw/ole/safearray.h"

3. Windows features checks

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All checks of features not present in all Windows versions must be done both at compile-time (because, even though we use maximal value for WINVER in our code, some compilers come with headers too old to declare them) and at run-time (because wxMSW applications should run everywhere).

The functions wxGetWinVersion() (from wx/msw/private.h) and wxApp:: GetComCtl32Version() should be used to check Windows and comctl32.dll versions respectively.

Any functions which may not be present in kernel32.dll/user32.dll/... in all Windows versions should be resolved dynamically, i.e. using wxDynamicLibrary as otherwise any wx application -- even not needing them at all -- would refuse to start up on Windows versions not implementing the feature in question. As an example, look at AlphaBlt()-related code in src/msw/dc.cpp.