Window positioning results in space around windows on Windows 10 - windows

Question

I have some code that positions windows to screen quadrants. It works fine on Windows XP, 7, and 8/8.1. However, on Windows 10, there is a weird gap between windows. The extra space surrounds the window on all 4 sides. I presume it has something to do with window borders, but can't figure out how to correct the problem. Any input would be highly appreciated. The code is as follows:
// Get monitor info
HMONITOR hm = MonitorFromWindow(hWnd, MONITOR_DEFAULTTONEAREST);
MONITORINFO mi;
mi.cbSize = sizeof(mi);
GetMonitorInfo(hm, &mi);
// Set screen coordinates and dimensions of monitor's work area
DWORD x = mi.rcWork.left;
DWORD y = mi.rcWork.top;
DWORD w = mi.rcWork.right - x;
DWORD h = mi.rcWork.bottom - y;
switch (corner) {
case 0: // Left top
SetWindowPos(hWnd, HWND_TOP, x, y, w / 2, h / 2, SWP_NOZORDER);
break;
case 1: // Right top
SetWindowPos(hWnd, HWND_TOP, x + w / 2, y, w / 2, h / 2, SWP_NOZORDER);
break;
case 2: // Right bottom
SetWindowPos(hWnd, HWND_TOP, x + w / 2, y + h / 2, w / 2, h / 2, SWP_NOZORDER);
break;
case 3: // Left bottom
SetWindowPos(hWnd, HWND_TOP, x, y + h / 2, w / 2, h / 2, SWP_NOZORDER);
break;
}

Answer 1

I managed to correct this effect by inflating target rectangle by a calculated margin like this:
static RECT GetSystemMargin(IntPtr handle) {
HResult success = DwmGetWindowAttribute(handle, DwmApi.DWMWINDOWATTRIBUTE.DWMWA_EXTENDED_FRAME_BOUNDS,
out var withMargin, Marshal.SizeOf<RECT>());
if (!success.Succeeded) {
Debug.WriteLine($"DwmGetWindowAttribute: {success.GetException()}");
return new RECT();
}
if (!GetWindowRect(handle, out var noMargin)) {
Debug.WriteLine($"GetWindowRect: {new Win32Exception()}");
return new RECT();
}
return new RECT {
left = withMargin.left - noMargin.left,
top = withMargin.top - noMargin.top,
right = noMargin.right - withMargin.right,
bottom = noMargin.bottom - withMargin.bottom,
};
}
And then doing
RECT systemMargin = GetSystemMargin(this.Handle);
targetBounds.X -= systemMargin.left;
targetBounds.Y -= systemMargin.top;
targetBounds.Width += systemMargin.left + systemMargin.right;
targetBounds.Height += systemMargin.top + systemMargin.bottom;
That worked for all windows I could test it with, except Explorer windows, which I hardcoded to exclude. If I'd do that expansion on Explorer near the screen edge, window ends up spilling a large area past it to the adjacent monitor.

Answer 2

The default font size of windows XP/7/8/8.1 is 100%, but in windows 10 the default is to display text and items in 125%. That affects directly all the window sizes.
Go to settings, display and you will find a scroller, move it to 100% and everything should display the same way as it did in Windows 8/7/XP