libui/windows/util.c

// 6 april 2015
#include "uipriv_windows.h"

intmax_t uiWindowsWindowTextWidth(HWND hwnd)
{
	LRESULT len;
	WCHAR *text;
	HDC dc;
	HFONT prevfont;
	SIZE size;

	size.cx = 0;
	size.cy = 0;

	// first we need the window text
	len = SendMessageW(hwnd, WM_GETTEXTLENGTH, 0, 0);
	if (len == 0)		// no text; nothing to do
		return 0;
	text = (WCHAR *) uiAlloc((len + 1) * sizeof (WCHAR), "WCHAR[]");
	// note the comparison: the size includes the null terminator, but the return does not
	if (GetWindowText(hwnd, text, len + 1) != len)
		logLastError("error getting window text in uiWindowsWindowTextWidth()");

	// now we can do the calculations
	dc = GetDC(hwnd);
	if (dc == NULL)
		logLastError("error getting DC in uiWindowsWindowTextWidth()");
	prevfont = (HFONT) SelectObject(dc, hMessageFont);
	if (prevfont == NULL)
		logLastError("error loading control font into device context in uiWindowsWindowTextWidth()");
	if (GetTextExtentPoint32W(dc, text, len, &size) == 0)
		logLastError("error getting text extent point in uiWindowsWindowTextWidth()");
	if (SelectObject(dc, prevfont) != hMessageFont)
		logLastError("error restoring previous font into device context in uiWindowsWindowTextWidth()");
	if (ReleaseDC(hwnd, dc) == 0)
		logLastError("error releasing DC in uiWindowsWindowTextWidth()");
	uiFree(text);

	return size.cx;
}

// this is a helper function that takes the logic of determining window classes and puts it all in one place
// there are a number of places where we need to know what window class an arbitrary handle has
// theoretically we could use the class atom to avoid a _wcsicmp()
// however, raymond chen advises against this - http://blogs.msdn.com/b/oldnewthing/archive/2004/10/11/240744.aspx (and we're not in control of the Tab class, before you say anything)
// usage: windowClassOf(hwnd, L"class 1", L"class 2", ..., NULL)
int windowClassOf(HWND hwnd, ...)
{
// MSDN says 256 is the maximum length of a class name; add a few characters just to be safe (because it doesn't say whether this includes the terminating null character)
#define maxClassName 260
	WCHAR classname[maxClassName + 1];
	va_list ap;
	WCHAR *curname;
	int i;

	if (GetClassNameW(hwnd, classname, maxClassName) == 0)
		logLastError("error getting name of window class in windowClassOf()");
	va_start(ap, hwnd);
	i = 0;
	for (;;) {
		curname = va_arg(ap, WCHAR *);
		if (curname == NULL)
			break;
		if (_wcsicmp(classname, curname) == 0) {
			va_end(ap);
			return i;
		}
		i++;
	}
	// no match
	va_end(ap);
	return -1;
}

void complain(const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vfprintf(stderr, fmt, ap);
	va_end(ap);
	abort();
}