Callback function passed to EnumFontFamiliesExW uses wrong signature

[beevvy]

Example callback function used with EnumFontFamiliesExW:

int CALLBACK FontEnumForV2Console(ENUMLOGFONT *pelf, NEWTEXTMETRIC *pntm, int nFontType, LPARAM lParam);

But FONTENUMPROC as expected by EnumFontFamiliesExW is defined as follows (SDK 10.0.18362.0):

typedef int (CALLBACK* OLDFONTENUMPROCW)(CONST LOGFONTW *, CONST TEXTMETRICW *, DWORD, LPARAM);

In practice, the differing argument types are representation-compatible anyway, so it works fine, but it does require a cast on the function pointer. It was suggested in #871 to get this sorted out.

Affected files:

>git grep FONTENUMPROC
src/propsheet/misc.cpp:    EnumFontFamiliesEx(hDC, &LogFont, (FONTENUMPROC)((ShouldAllowAllMonoTTFonts()) ? FontEnumForV2Console : FontEnum), (LPARAM)&fed, 0);
src/renderer/gdi/tool/main.cpp:    EnumFontFamiliesExW( hDC, &lf, (FONTENUMPROC)EnumFontFamiliesExProc, 0, 0 );
src/tools/fontlist/main.cpp:    EnumFontFamiliesExW(hdc.get(), &LogFont, (FONTENUMPROC)FontEnumForV2Console, (LPARAM)hdc.get(), 0);

BTW, src/renderer/gdi/tool/main.cpp is not included in any project in the solution, preventing it to be scanned by an IDE. Is that intentional?

[HBelusca]

The actual problem here, I think, is that the function does really want to always use a NEWTEXTMETRIC pointer for its second argument (note: the ENUMLOGFONT pointer can be converted to a LOGFONTW pointer without problem).

[beevvy]

The documentation of EnumFontFamiliesExW links to a legacy doc of EnumFontFamExProc, which says:

lpntme
A pointer to a structure that contains information about the physical attributes of a font. The function uses the NEWTEXTMETRICEX structure for TrueType fonts; and the TEXTMETRIC structure for other fonts.
This can be an ENUMTEXTMETRIC structure.

I believe that the correct approach would be to use the specified function signature and just cast the second argument to NEWTEXTMETRICEX*. Just like you cast the LPTHREAD_START_ROUTINE's PVOID argument to whatever type you expect.