How to detect double-click/tap when handling WM_POINTER message?

Question

I am trying to implement Pointer Input Messages to replace regular mouse message in a window. I'm doing this to have a better support of stylus input in my program. Everything works fine except for double-click.

I didn't process pointer message before, so these pointer messages posted by stylus driver were just passed to DefWindowProc and DefWindowProc just generated mouse input like WM_LBUTTONDBLCLK.

Unlike mouse message WM_LBUTTONDBLCLK, there is no pointer message that would explicitly tell you it's a double click. I understand their intention of designing a concise group of messages and make everything else in a clean single structure. POINTER_PEN_INFO is that struct which contains all information associated with the current message. I thought I could find anything there, maybe some flags to indicate that a WM_POINTERDOWN message should be treated as a double click, but nothing is there as well.

Is there anything I missed? If not, what else could I do to detect a double-click? I could only find some antiquated documents that was written for Window XP on MSDN. I'm programming on Windows 10, Win32 API programming with C++.

Thank you!

Answer 1

You can do this by tracking clicks and comparing each click to the last in the same way that Windows does.

Pseudo-code:

POINT ptLastClickPos;
DWORD dwLastClickTime;

if (uMsg == WM_POINTERDOWN)
{
    DWORD dwClickTime = GetMessageTime();
    POINT ptClickPos = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) };

    if (dwLastClickTime + GetDoubleClickTime() > dwClickTime
    &&  abs(ptLastClickPos.x - ptClickPos.x) < GetSystemMetrics(SM_CXDOUBLECLK)
    &&  abs(ptLastClickPos.y - ptClickPos.y) < GetSystemMetrics(SM_CYDOUBLECLK))
    {
        // double-click!
    }
    else
    {
        dwLastClickTime = dwClickTime;
        ptLastClickPos = ptClickPos;
    }
}