This section describes the basic steps for using multitouch gestures.
The following steps are typically performed when using Windows Touch gestures:
- Set up a window for receiving gestures.
- Handle the gesture messages.
- Interpret the gesture messages.
Setting up a Window to Receive Gestures
By default, you receive WM_GESTURE messages.
Note If you call RegisterTouchWindow, you will stop receiving WM_GESTURE messages. If you are not receiving WM_GESTURE messages, make sure that you haven't called RegisterTouchWindow.
The following code shows a simple InitInstance implementation.
#include <windows.h> BOOL InitInstance(HINSTANCE hInstance, int nCmdShow) { HWND hWnd; hInst = hInstance; // Store instance handle in our global variable hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL); if (!hWnd) { return FALSE; } ShowWindow(hWnd, nCmdShow); UpdateWindow(hWnd); return TRUE; }
Handling Gesture Messages
Similar to handling Windows Touch input messages, you can handle gesture messages in many ways. If you are using Win32, you can check for the WM_GESTURE message in WndProc. If you are creating another type of application, you can add the WM_GESTURE message to the message map and then implement a custom handler.
The following code shows how gesture messages could be handled.
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
switch (message)
{
case WM_GESTURE:
// Insert handler code here to interpret the gesture.
return DecodeGesture(hWnd, message, wParam, lParam);
Interpreting the Gesture Messages
The GetGestureInfo function is used to interpret a gesture message into a structure describing the gesture. The structure, GESTUREINFO, has information about the gesture such as the location where the gesture was performed and the type of gesture. The following code shows how you can retrieve and interpret a gesture message.
LRESULT DecodeGesture(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam){
// Create a structure to populate and retrieve the extra message info.
GESTUREINFO gi;
ZeroMemory(&gi, sizeof(GESTUREINFO));
gi.cbSize = sizeof(GESTUREINFO);
BOOL bResult = GetGestureInfo((HGESTUREINFO)lParam, &gi);
BOOL bHandled = FALSE;
if (bResult){
// now interpret the gesture
switch (gi.dwID){
case GID_ZOOM:
// Code for zooming goes here
bHandled = TRUE;
break;
case GID_PAN:
// Code for panning goes here
bHandled = TRUE;
break;
case GID_ROTATE:
// Code for rotation goes here
bHandled = TRUE;
break;
case GID_TWOFINGERTAP:
// Code for two-finger tap goes here
bHandled = TRUE;
break;
case GID_PRESSANDTAP:
// Code for roll over goes here
bHandled = TRUE;
break;
default:
// A gesture was not recognized
break;
}
}else{
DWORD dwErr = GetLastError();
if (dwErr > 0){
//MessageBoxW(hWnd, L"Error!", L"Could not retrieve a GESTUREINFO structure.", MB_OK);
}
}
if (bHandled){
return 0;
}else{
return DefWindowProc(hWnd, message, wParam, lParam);
}
}