Windows multi touch TOUCHEVENTF_UP not received

Question

I am working on an app for Windows that supports multitouch. I have followed the guide found here

http://msdn.microsoft.com/en-us/library/windows/desktop/dd744775(v=vs.85).aspx

but i have a problem. At some point there is a stuck finger meaning that i can see that there is a TOUCHEVENTF_DOWN, a TOUCHEVENTF_MOVE but NO TOUCHEVENTF_UP for this finger although there is no fingers any more on the screen...

I have:

static int fingers = 0;
static LRESULT OnTouch(HWND hWnd, WPARAM wParam, LPARAM lParam );
static LRESULT CALLBACK winProc(HWND hwnd, UINT Msg, WPARAM wParam, LPARAM lParam);

SetWindowLongPtr(handle, GWL_WNDPROC, (long)winProc);

LRESULT CALLBACK winProc(HWND hwnd, UINT Msg, WPARAM wParam, LPARAM lParam){
    switch(Msg){
    case WM_TOUCH:
        OnTouch(handle, wParam, lParam);
        break;
...
}

LRESULT OnTouch(HWND hWnd, WPARAM wParam, LPARAM lParam )
{
    BOOL bHandled = FALSE;
    UINT cInputs = LOWORD(wParam);
    PTOUCHINPUT pInputs = new TOUCHINPUT[cInputs];
    if (pInputs){
        if (GetTouchInputInfo((HTOUCHINPUT)lParam, cInputs, pInputs, sizeof(TOUCHINPUT))){
            for (UINT i=0; i < cInputs; i++){
            TOUCHINPUT ti = pInputs[i];
            if( ti.dwFlags&TOUCHEVENTF_DOWN ) {
                        fingers+=1;
            }
            else {
                if( ti.dwFlags&TOUCHEVENTF_MOVE) {
                }
                if( ti.dwFlags&TOUCHEVENTF_UP) {
                            fingers-=1;
                }
            }
            bHandled = TRUE;
        }else{
            /* handle the error here */
        }
        delete [] pInputs;
    }else{
        /* handle the error here, probably out of memory */
    }
    if (bHandled){
        // if you handled the message, close the touch input handle and return
        CloseTouchInputHandle((HTOUCHINPUT)lParam);
        return 0;
    }else{
        // if you didn't handle the message, let DefWindowProc handle it
        printf("ERROR\n");
        return DefWindowProc(hWnd, WM_TOUCH, wParam, lParam);
    }
}

After touching the screen i end up with no actual fingers on the screen but with the variable fingers != 0....

I would appreciate some help. Thanks.

P.S. I applied the proposed change but i still get stuck fingers, no finger up received.

score 2 · Answer 1 · answered Dec 05 '13 at 20:32

2

TOUCHEVENTF_MOVE and TOUCHEVENTF_UP can be combined in the one input, but you are testing for them as if they are exclusive values. Therefore if a 'move' and an 'up' come at the same time you'll miss the 'up'.

The docs for the TOUCHINPUT structure specify which flags make sense in combination.

answered Dec 05 '13 at 20:32

Jonathan Potter

36,172
4
64
79

Thank u! I completely ignored the combined part when i was reading the doc. – thodoris Dec 06 '13 at 07:35
I updated my code (see above), but i still have the same issue.Any other suggestions? – thodoris Dec 09 '13 at 11:22

Windows multi touch TOUCHEVENTF_UP not received

1 Answers1