send mouse click to winamp

Question

I'm trying to learn mouse/keyboard emulation using win api.
I found out that it is possible to emulate button click using sendmessage() function.

Well, I get coordinates of "play" button (it is (60;100)) and trying to push this button using the following code:

            int x = 60;
            int y = 100;
            int lParam = ((x << 16) | (y & 0xffff));

            int parentWindow = FindWindow("BaseWindow_RootWnd", "Main Window");//get main winamp window
            MessageBox.Show(parentWindow.ToString());//failed if 0

            SendMessage(parentWindow, WM_LBUTTONDOWN, IntPtr.Zero, new IntPtr(lParam));//send left mouse button down
            SendMessage(parentWindow, WM_LBUTTONUP, IntPtr.Zero, new IntPtr(lParam));//send left mouse button up

But this code has no effect on the winamp.

Can anybody point me on the mistakes i made? Any help is greatly appreciated!

p.s. It's not applicable for me to move mouse to the winamp play button, than do a click, than move it back.
Also for winamp it is impossible to get button's handle. With button handle SendMessage() works fairly well, but with coordinates it doesn't at all.

ADDITION #1

Well, the code above activates winamp window and shows it, if it was minimized. But play button stil don't want to be pushed ;(

ADDITION #2

Here are messages I get after I execute the code above.

Answer 1

well, to simulate mouse click in winamp window you need to do exactly what is happening when you just click it with hardware mouse. The following was found out from spy++:

So to emulate mouse click we need to:

1. Call twice PostMessage() instead of SendMessage() because "P" in the screenshot above tells us that the message was got from the PostMessage() (according to msdn)
2. The parameters should be the following for the first PostMessage():
   - First parameter - Winamp window handle (in our case it is 005E09FA)
   - Second parameter - the winapi code of the event, when left mouse button is down(WM_LBUTTONDOWN = 0x201)
   - Third parameter - MK_LBUTTON = 0x1 (It seems, it is necessary to pass it. It would be great if somebody can explain why)
   - Fourth parameter - Coordinates of the point where you want to press mouse button (this parameter can be calculated as following - ((Y << 16) | X))
3. The parameters should be the following for the second PostMessage():
   - First parameter - Winamp window handle (in our case it is 005E09FA)
   - Second parameter - the winapi code of the event, when left mouse button is up (WM_LBUTTONUP = 0x202)
   - Third parameter - 0 or IntPtr.Zero
   - Fourth parameter - Coordinates of the point where you want to release mouse button (need to be as in first PostMessage() if you want your click to have an effect; this parameter can be calculated as following - ((Y << 16) | X))

Thanks everyone for their input!

Answer 2

To let Winamp play/pause the current song, simply send it a Play/Pause message, which is long 40046 as defined in winamp.h. You'll have to send it in a WM_WA_IPC message (which is a user message, also known as WM_USER) instead of a WM_LBUTTONDOWN.

So, something like this should do:

SendMessage(parentWindow, WM_USER, IntPtr.Zero, new IntPtr(40046));

More info here, here and here.

Answer 3

You should be using SendInput() to send input to other applications, not faking window messages.