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Getting Started with Windows Touch Messages

  • Článek

This section explains the tasks associated with getting Windows Touch input to function in your application.

The following steps are typically performed when working with Windows Touch messages:

  1. Test the capabilities of the input digitizer.
  2. Register to receive Windows Touch messages.
  3. Handle the messages.

The message used for Windows Touch is WM_TOUCH. This message indicates the various states of contact with a digitizer.

Testing the Capabilities of the Input Digitizer

The GetSystemMetrics function can be used to query the capabilities of the input digitizer by passing in the nIndex value of SM_DIGITIZER. GetSystemMetrics returns a bit field that indicates whether the device is ready, whether the device supports pen or touch, whether the input device is integrated or external, and whether the device supports multiple inputs (Windows Touch). The following table shows the bits for the various fields.

Bit 8 7 6 5 4 3 2 1
Value Stack Ready Multi-input Reserved Reserved External Pen Integrated Pen External Touch Integrated Touch

 

To test the result from the command for a particular feature, you can use the bitwise & operator and the particular bit you are testing. For example, to test for Windows Touch, you would test that the seventh-order bit is set (0x40 in hex). The following code example shows how these values could be tested.

#include <windows.h>

// test for touch
int value = GetSystemMetrics(SM_DIGITIZER);
if (value & NID_READY){ /* stack ready */}
if (value  & NID_MULTI_INPUT){
    /* digitizer is multitouch */ 
    MessageBoxW(hWnd, L"Multitouch found", L"IsMulti!", MB_OK);
}
if (value & NID_INTEGRATED_TOUCH){ /* Integrated touch */}

The following table lists the constants defined in windows.h for testing touch capabilities of the input digitizer.

Name Value Description
TABLET_CONFIG_NONE 0x00000000 The input digitizer does not have touch capabilities.
NID_INTEGRATED_TOUCH 0x00000001 An integrated touch digitizer is used for input.
NID_EXTERNAL_TOUCH 0x00000002 An external touch digitizer is used for input.
NID_INTEGRATED_PEN 0x00000004 An integrated pen digitizer is used for input.
NID_EXTERNAL_PEN 0x00000008 An external pen digitizer is used for input.
NID_MULTI_INPUT 0x00000040 An input digitizer with support for multiple inputs is used for input.
NID_READY 0x00000080 The input digitizer is ready for input. If this value is unset, it may mean that the tablet service is stopped, the digitizer is not supported, or digitizer drivers have not been installed.

 

Checking the NID_* values is a useful way of checking the capabilities of a user's computer to configure your application for touch, pen, or non-tablet input. For example, if you have a dynamic user interface (UI) and want to automatically configure some of it, you could check for NID_INTEGRATED_TOUCH, NID_MULTITOUCH, and could get the maximum number of touches the first time that a user runs your application.

Note

There are some inherent limitations for SM_GETSYSTEMMETRICS. For example, there is no support for plug and play. For this reason, use caution when using this function as a means for permanent configuration.

 

Registering to Receive Windows Touch Input

Before receiving Windows Touch input, applications must first register to receive Windows Touch input. By registering the application window, the application indicates that it is touch compatible. After the application registers its window, notifications from the Windows Touch driver are forwarded to the application when input is made on the window. When the application shuts down, it unregisters its window to disable notifications.

Note

WM_TOUCH messages are currently "greedy." After the first touch message is received on a window, all touch messages are sent to that window until another window receives focus.

 

Note

By default, you receive WM_GESTURE messages instead of WM_TOUCH messages. If you call RegisterTouchWindow, you will stop receiving WM_GESTURE messages.

 

The following code demonstrates how an application could register to receive Windows Touch messages in a Win32 application.

RegisterTouchWindow(hWnd, 0);

Handling Windows Touch Messages

You can handle the Windows Touch messages from applications in Windows operating systems in many ways. If you are programming a GUI application, you add code within the WndProc function to handle the messages of interest. If you are programming a Microsoft Foundation Class (MFC) or managed application, you add handlers for the messages of interest. The following code example shows how touch messages could be handled from WndProc in a Windows-based application.

  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];
                //do something with each touch input entry
            }            
            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
        return DefWindowProc(hWnd, WM_TOUCH, wParam, lParam);
    }
  }


LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    int wmId, wmEvent;
    PAINTSTRUCT ps;
    HDC hdc;

    switch (message)
    {
      // pass touch messages to the touch handler 
      case WM_TOUCH:
        OnTouch(hWnd, wParam, lParam);
        break;

The following code shows how you can implement the message map and a message handler. Note that the messages must be declared in the message map and then the handler for the message should be implemented. For example, in an MFC application, this could be declared in the dialog code. Note also, that the OnInitDialog function for your dialog window would have to include a call to RegisterTouchWindow such as RegisterTouchWindow(m_hWnd, 0).

  // Class implementations within a dialog
  LRESULT TestDlg::OnTouch( WPARAM wParam, LPARAM lParam ){
    //Insert handler code here to do something with the message or uncomment the following line to test
    //MessageBox(L"touch!", L"touch!", MB_OK);
    return 0;
  }
  // The message map
  BEGIN_MESSAGE_MAP()
    ON_WM_CREATE()
    ... ... ...
    ON_MESSAGE(WM_TOUCH, OnTouch)
  END_MESSAGE_MAP()  
 
  BOOL TestDlg::OnInitDialog()
  {
    CDialog::OnInitDialog();    

    RegisterTouchWindow(m_hWnd, 0);
     ... ... ...
  }

Touching the window will indicate touches from a pop-up window.

Windows Touch Input