WM_MOUSEMOVE issues with position

Question

I am working on a program that is supposed to simulate basic mouse input for a program while it stays in the background (meaning, I want to do other things in other windows with the actual mouse and keyboard while the target receives input). One thing I need to be able to do is move the mouse to a specific (x,y) point.

It seems to work for the most part, but in a certain region of the screen the message only works correctly some of the time. Other times, it moves to a consistent but wrong other point within the region. I am reading that sometimes it is relative, but if I spam the message repeatedly, it does seem to work consistently. Also, reading in Spy++, the messages that are sent by me actually moving my mouse are using what seem to be absolute coordinates.

My function is here:

void mouseMove(short x, short y) {
    PostMessage(wnd, WM_MOUSEMOVE, 0, MAKELPARAM(x, y));
}

Preferably, I'd like for any (x,y) to be absolute so I can have the region treated as any other. But it would also be fine to set the position to a coordinate relative to the top left corner of the region.

I have tried just about all of the messages I've seen sent to the window in Spy++ before the WM_MOUSEMOVE but nothing is helping.

How might I approach this?

Edit, since details might not prove enough info:

I am sending these messages in this order:

• WM_ACTIVATE 2 0
• WM_MOUSEMOVE 0 MAKELPARAM(x,y)
• WM_LBUTTONDOWN MK_LBUTTON MAKELPARAM(x,y)
• WM_LBUTTONUP 0 MAKELPARAM(x,y)

I think what I initially thought (bad WM_SETCURSOR area) is wrong because Spy++ consistently shows HTCLIENT being used.

I have found a lot of people trying to do this (background input) and most seem to be told it's impossible. It's not impossible, and I think if someone can answer how to do this correctly once and for all it would be doing quite a few people a big favor.

Answer 1

Synthesizes keystrokes, mouse motions, and button clicks.

   UINT WINAPI SendInput(
      _In_ UINT    nInputs,
      _In_ LPINPUT pInputs,
      _In_ int     cbSize
    );

PostMessage function. Places (posts) a message in the message queue associated with the thread that created the specified window and returns without waiting for the thread to process the message.

For PostMessage to work you need to be in the process as the target that you can achieve with SetWindowHook but the these links will do the jobs:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms646310(v=vs.85).aspx https://msdn.microsoft.com/en-us/library/ms171542(v=vs.110).aspx