MouseDown and then MouseUp doesn't work - winapi

Question

I am trying to redirect mouse inputs on my Windows 7 application to some other window.
If I do this when I get WM_LBUTTONUP, it works (where MouseDown and MouseUp are SendInput functions in Win api):
SetForegroundWindow( other window );
SetCursorPos( somewhere on the window );
MouseDown();
MouseUp();
SetCursorPos( back );
SetForegroundWindow( main window );
But I don't want to only do mouse releases, I want to be able to capture all mouse stuff, including movements and dragging.
So this is next logical thing to do but it doesn't work:
WM_LBUTTONDOWN:
Do everything like before without MouseUp()
WM_LBUTTONUP:
Do everything like before without MouseDown()
This doesn't even work for regular clicks. I can't figure out why.
Can anybody help?

Answer 1

Mouse buttons are funky. When it gets an down then up, at some level those are converted to a click (and I think at some point the mouse up gets eaten, but I may not be recalling that correctly).
It could be any number of things, but if the other windows is (or is not) converting the buttondown/up to mouse clicks, it could be confusing your code.
I suggest you print a lot of debugging info and try to figure out exactly what the system is doing.

Answer 2

It might be worth looking at the SendMessage/PostMessage P/Invoke calls, and sending the messages directly to the window of the other application. You need to do some translation on the parameters so that the co-ordinates of mouse events tie up with what you want them to in the other application, but it's not a big deal to do that...
Edit -> I dug out some code where I have done this before... This is from a window which appears over the top of a tree view and replaces the default windows tooltip for that tree view.
private IntPtr _translate(IntPtr LParam)
{
// lparam is currently in client co-ordinates, and we need to translate those into client co-ordinates of
// the tree view we're attached to
int x = (int)LParam & 0xffff;
int y = (int)LParam >> 16;
Point screenPoint = this.PointToScreen(new Point(x, y));
Point treeViewClientPoint = _tv.PointToClient(screenPoint);
return (IntPtr)((treeViewClientPoint.Y << 16) | (treeViewClientPoint.X & 0xffff));
}
const int MA_NOACTIVATE = 3;
protected override void WndProc(ref Message m)
{
switch ((WM)m.Msg)
{
case WM.LBUTTONDBLCLK:
case WM.RBUTTONDBLCLK:
case WM.MBUTTONDBLCLK:
case WM.XBUTTONDBLCLK:
{
IntPtr i = _translate(m.LParam);
_hide();
InteropHelper.PostMessage(_tv.Handle, m.Msg, m.WParam, i);
return;
}
case WM.MOUSEACTIVATE:
{
m.Result = new IntPtr(MA_NOACTIVATE);
return;
}
case WM.MOUSEMOVE:
case WM.MOUSEHWHEEL:
case WM.LBUTTONUP:
case WM.RBUTTONUP:
case WM.MBUTTONUP:
case WM.XBUTTONUP:
case WM.LBUTTONDOWN:
case WM.RBUTTONDOWN:
case WM.MBUTTONDOWN:
case WM.XBUTTONDOWN:
{
IntPtr i = _translate(m.LParam);
InteropHelper.PostMessage(_tv.Handle, m.Msg, m.WParam, i);
return;
}
}
base.WndProc(ref m);
}