font.c

#include <windows.h>
#include <uxtheme.h>
#include <vssym32.h>

// window is a top-level HWND

static HFONT get_control_font_textstyle(void)
{
	HTHEME textstyle = OpenThemeData(window, VSCLASS_TEXTSTYLE);
	if (!textstyle)
		return NULL;

	LOGFONTW logfont;
	HRESULT res = GetThemeFont(textstyle, NULL, TEXT_CONTROLLABEL, 0, TMT_FONT,
	                           &logfont);
	CloseThemeData(textstyle);
	if (res != S_OK)
		return NULL;

	return CreateFontIndirectW(&logfont);
}

static HFONT get_control_font_sys(void)
{
	HTHEME theme = OpenThemeData(window, VSCLASS_WINDOW);
	if (!theme)
		return NULL;

	LOGFONTW logfont;
	HRESULT res = GetThemeSysFont(theme, TMT_MENUFONT, &logfont);
	CloseThemeData(theme);
	if (res != S_OK)
		return NULL;

	return CreateFontIndirectW(&logfont);
}

static HFONT get_control_font_ncm(void)
{
	NONCLIENTMETRICSW ncm = {
		.cbSize = sizeof(NONCLIENTMETRICSW),
	};

	if (!SystemParametersInfoW(SPI_GETNONCLIENTMETRICS, sizeof(ncm), &ncm, 0))
		return NULL;
	return CreateFontIndirectW(&ncm.lfMenuFont);
}

/* get_control_font - nothing is trivial in Windows, even (especially?) getting
   the system font */
static HFONT get_control_font(void)
{
	HFONT font;

	/* Only Windows Vista and up have the TextStyle class. If the class is
	   missing, use the system menu font instead. */
	if ((font = get_control_font_textstyle())) return font;
	if ((font = get_control_font_sys())) return font;

	/* If both UXTheme methods fail, try the old fashioned NONCLIENTMETRICS
	   structure */
	if ((font = get_control_font_ncm())) return font;

	return NULL;
}