Changes the resolution of a display on Windows. Useful for fixing the size of Wine's virtual desktop.

winfixres.c

/**
 * Changes the resolution of a display on Windows.
 * Useful for fixing the size of Wine's virtual desktop.
 *
 * Released into the public domain.
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

#include <stdio.h>
#include <wchar.h>
#include <windows.h>

const wchar_t *progname = L"winfixres";

__attribute__((noreturn))
static void usageQuit(void)
{
	fwprintf(stderr,
		L"Usage: %ls -l\n"
		L"       %ls DEVICENUM WIDTH HEIGHT\n",
		progname, progname
	);
	exit(1);
}

static size_t parseUIntOrQuit(const wchar_t *s)
{
	wchar_t *end;
	size_t ret;

	if (s == NULL)
	{
		fwprintf(stderr, L"Expected number, got NULL string.\n");
		usageQuit();
	}
	else if (s[0] == L'\0')
	{
		fwprintf(stderr, L"Expected number, got zero-length string.\n");
		usageQuit();
	}

	errno = 0;
	ret = wcstoul(s, &end, 0);

	if (errno != 0)
	{
		fwprintf(stderr, L"Error parsing number '%ls'.\n", s);
		usageQuit();
	}
	else if (end[0] != L'\0')
	{
		fwprintf(stderr, L"Found invalid character (%lc) in number '%ls'.\n", end[0], s);
		usageQuit();
	}

	return ret;
}

static void listDevices(void)
{
	DWORD i;
	DISPLAY_DEVICEW ddev;

	ddev.cb = sizeof(ddev);

	for (i = 0; ; ++i)
	{
		if (!EnumDisplayDevicesW(NULL, i, &ddev, 0))
		{
			/* failed; probably no more display devices */
			break;
		}

		wprintf(L"%3lu: %ls\n", i, ddev.DeviceString);
	}
}

static int changeRes(size_t devnum, size_t w, size_t h)
{
	DISPLAY_DEVICEW ddev;
	DEVMODEW dm;
	LONG ret;

	ddev.cb = sizeof(ddev);
	dm.dmSize = sizeof(dm);
	dm.dmDriverExtra = 0;

	if (!EnumDisplayDevicesW(NULL, devnum, &ddev, 0))
	{
		fwprintf(stderr, L"Display #%lu doesn't exist.\n", devnum);
		return 2;
	}

	if (!EnumDisplaySettingsExW(
		ddev.DeviceName,
		ENUM_CURRENT_SETTINGS,
		&dm,
		0
	))
	{
		fwprintf(stderr, L"Failed to fetch current display settings.\n");
		return 2;
	}

	dm.dmPelsWidth = w;
	dm.dmPelsHeight = h;
	dm.dmFields |= (DM_PELSWIDTH | DM_PELSHEIGHT);

	ret = ChangeDisplaySettingsExW(
		ddev.DeviceName,
		&dm,
		NULL,
		0,
		NULL
	);

	switch (ret)
	{
		case DISP_CHANGE_SUCCESSFUL:
			return 0;
		case DISP_CHANGE_BADDUALVIEW:
			fwprintf(stderr, L"Failed to change video mode: bad dual view.\n");
			return 2;
		case DISP_CHANGE_BADFLAGS:
			fwprintf(stderr, L"Failed to change video mode: bad flags.\n");
			return 2;
		case DISP_CHANGE_BADMODE:
			fwprintf(stderr, L"Failed to change video mode: unsupported mode.\n");
			return 2;
		case DISP_CHANGE_BADPARAM:
			fwprintf(stderr, L"Failed to change video mode: invalid parameter.\n");
			return 2;
		case DISP_CHANGE_FAILED:
			fwprintf(stderr, L"Failed to change video mode: driver failed the mode.\n");
			return 2;
		case DISP_CHANGE_NOTUPDATED:
			fwprintf(stderr, L"Warning: Failed to store video mode into registry.\n");
			return 0;
		case DISP_CHANGE_RESTART:
			fwprintf(stderr, L"Warning: The computer must be restarted for this mode to work.\n");
			return 0;
	}

	return 3;
}

int wmain(int argc, wchar_t **argv)
{
	if (argc > 0)
	{
		progname = argv[0];
	}

	if (argc == 2 && argv[1][0] == '-')
	{
		if (wcscmp(argv[1], L"-l") == 0)
		{
			listDevices();
		}
		else
		{
			usageQuit();
		}
	}
	else if (argc == 4)
	{
		size_t devnum = parseUIntOrQuit(argv[1]);
		size_t w = parseUIntOrQuit(argv[2]);
		size_t h = parseUIntOrQuit(argv[3]);

		return changeRes(devnum, w, h);
	}
	else
	{
		usageQuit();
	}

	return 0;
}