A customer had a program which responded to left mouse clicks, but they found that when used with a touch screen, when users touched the screen, the WM_LBUTTON­DOWN message didn’t arrive until the users lifted their fingers from the screen. They wanted to know whether this was by design, and also whether there was a way to get the WM_LBUTTON­DOWN message as soon as the finger touches the screen.

Yes, this behavior is by design. The system is waiting to see whether the user is making a press-and-hold gesture. If so, then the touch events are converted to right-mouse-button messages (WM_RBUTTON­DOWN and WM_RBUTTON­UP). But if the finger does not remain in contact for a long time, then the touch events are converted to left-mouse-button messages (WM_LBUTTON­DOWN and WM_LBUTTON­UP).

The customer’s program was targeting Windows 7, so they were looking for solutions that would work on that platform.

Take our scratch program and add the following:

#include <strsafe.h> // StringCchPrintf
#include <tpcshrd.h> // WM_TABLET_QUERYSYSTEMGESTURESTATUS

BOOL
OnCreate(HWND hwnd, LPCREATESTRUCT lpcs)
{
  g_hwndChild = CreateWindow(TEXT("listbox"), NULL,
        LBS_HASSTRINGS | WS_CHILD | WS_VISIBLE | WS_VSCROLL,
        0, 0, 0, 0, hwnd, NULL, g_hinst, 0);
  return TRUE;
}

void
OnSize(HWND hwnd, UINT state, int cx, int cy)
{
    if (g_hwndChild) {
        MoveWindow(g_hwndChild, 0, 0, cx, cy/2, TRUE);
    }
}


LRESULT CALLBACK
WndProc(HWND hwnd, UINT uiMsg, WPARAM wParam, LPARAM lParam)
{
  ...
  case WM_LBUTTONDOWN:
  case WM_LBUTTONUP:
  case WM_RBUTTONDOWN:
  case WM_RBUTTONUP:
  {
    TCHAR buffer[80];
    StringCchPrintf(buffer, 80, TEXT("%04x %d %d"), uiMsg,
                    GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));
    ListBox_AddString(g_hwndChild, buffer);
  }
  break;

  case WM_TABLET_QUERYSYSTEMGESTURESTATUS:
    return TABLET_DISABLE_PRESSANDHOLD;
  ...
}

Most of this code is just creating a logging window so we can see the message traffic. (Note that we divide cy by 2 in the OnSize function so that there is room at the bottom of the window for touch activity.)

The interesting part is adding a handler for the WM_TABLET_QUERY­SYSTEM­GESTURE­STATUS message and responding that we want to disable press-and-hold.

This successfully disables the press-and-hold gesture on Tablet PC (remember that?), allowing the left-button messages to be generated immediately upon contact. But it doesn’t help for Windows 7 and above. For that, we need something else:

BOOL
OnCreate(HWND hwnd, LPCREATESTRUCT lpcs)
{
  g_hwndChild = CreateWindow(TEXT("listbox"), NULL,
        LBS_HASSTRINGS | WS_CHILD | WS_VISIBLE | WS_VSCROLL,
        0, 0, 0, 0, hwnd, NULL, g_hinst, 0);

  GESTURECONFIG config;
  config.dwID = 0;
  config.dwWant = 0;
  config.dwBlock = GC_ALLGESTURES;
  SetGestureConfig(hwnd, 0, 1, &config, sizeof(config));

  return TRUE;
}

This time, we disable all gestures using Set­Gesture­Config. This takes care of Windows 7 and higher.

So there are your options: There’s a “Windows XP and Windows Vista” solution, and there’s a “Windows 7 and higher” solution. Or you can just play it safe and use both.