Win api in C#. MouseMove event can't catch quick moves

Question

I have created a small Window without border by WinApi functions in C#. I want to move this window when right mouse button is pressed. I am trying to catch a mouse offset by anylizing WM_MOUSEMOVE event. It seems to work and i can move my window holding Right Mouse Button.

But I am loosing control of the window when i move my mouse too fast. That's because my Window is too small and if mouse leaves window very quick it doesn'n recieve WM_MOUSEMOVE messages anymore and i can't calculate a MouseOffset to move my Window.

So, How I can fix that?

Answer 1

You need to call SetCapture to tell Windows that your hwnd wants all the events even when the mouse isn't physically over the window. http://msdn.microsoft.com/en-us/library/windows/desktop/ms646262(v=vs.85).aspx

Answer 2

You can tell Windows that the user actually moused down on the title bar and it will handle the rest automatically for you.

[DllImport("user32.dll", CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern bool ReleaseCapture();

[DllImport("user32.dll", CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern bool PostMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

internal const uint WM_NCLBUTTONDOWN = 0xA1;

internal const int HTCAPTION = 2; // Window captions
internal const int HTBOTTOMRIGHT = 17; // Bottom right corner

/// <summary>
/// Simulates a Windows drag on the window border or title.
/// </summary>
/// <param name="handle">The window handle to drag.</param>
/// <param name="dragType">A HT* constant to determine which part to drag.</param>
internal static void DragWindow(IntPtr handle, int dragType) {
    User32.ReleaseCapture();
    User32.PostMessage(handle, User32.WM_NCLBUTTONDOWN, new IntPtr(dragType), IntPtr.Zero);
}