Why do I get a WM_MOUSELEAVE after enabling window? - c

Question

After enabling a disabled child window, I try to turn mouse tracking on in WM_ENABLE only if mouse cursor is hovering over the window using TrackMouseEvent() with dwFlags of TRACKMOUSEEVENT structure set to TME_LEAVE. TrackMouseEvent() returns TRUE, but then right after calling it I get a WM_MOUSELEAVE message. This happens only under 2 conditions. With first condition, move cursor outside of child window, press Enter key to disable the window, then move cursor over the child window and press the Space key. With second condition, move the cursor over window, press Enter key to disable it, then before pressing the Space key move the cursor 1 pixel or more and then press the Space key. If you retest the second condition, but instead of moving cursor before you press the Space key, if you press the Space key right after you press the Enter key, mouse tracking is turned on properly. I've tried really hard to fix this but I've not been lucky so far. Can somebody please fix this code and explain why mouse tracking is being canceled when I'm trying to turn it on?
#include <windows.h>
const WCHAR g_szChildClassName[] = L"Childclass////";
HINSTANCE g_hInst;
LRESULT CALLBACK ChildProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
static BOOL bMouseTracking = FALSE;
switch(msg)
{
case WM_PAINT:
{
HDC hdc;
PAINTSTRUCT ps;
hdc = BeginPaint(hwnd, &ps);
if(hdc)
{
HBRUSH hbr = CreateSolidBrush(bMouseTracking?RGB(255, 0, 0):RGB(0, 0, 255));
if(hbr)
{
FillRect(hdc, &ps.rcPaint, hbr);
DeleteObject(hbr);
}
EndPaint(hwnd, &ps);
}
}
break;
case WM_MOUSEMOVE:
if(!bMouseTracking)
{
TRACKMOUSEEVENT tme = { 0 };
tme.cbSize = sizeof(TRACKMOUSEEVENT);
tme.dwFlags = TME_LEAVE;
tme.hwndTrack = hwnd;
bMouseTracking = TrackMouseEvent(&tme);
InvalidateRect(hwnd, 0, TRUE);
}
break;
case WM_MOUSELEAVE:
bMouseTracking = FALSE;
InvalidateRect(hwnd, 0, TRUE);
break;
case WM_ENABLE:
if(wParam)
{
RECT rc;
if(GetWindowRect(hwnd, &rc))
{
POINT pt;
if(GetCursorPos(&pt))
if(PtInRect(&rc, pt))
{
TRACKMOUSEEVENT tme = { 0 };
tme.cbSize = sizeof(TRACKMOUSEEVENT);
tme.dwFlags = TME_LEAVE;
tme.hwndTrack = hwnd;
//TrackMouseEvent() posts WM_MOUSELEAVE if conditions 1 and 2 are met, even though I'm trying to turn
//mouse tracking on and the cursor is over the child window. It doesn't make sense
//The problems is this piece of code right here /* bMouseTracking = TrackMouseEvent(&tme); */
//It should turn tracking on but it doesn't it cancels it even though WS_DISABLED has already been removed
//at this point
bMouseTracking = TrackMouseEvent(&tme);
InvalidateRect(hwnd, 0, TRUE);
}
}
} else {
if(bMouseTracking) {
////////If you comment everything from here ...
TRACKMOUSEEVENT tme = { 0 };
tme.cbSize = sizeof(TRACKMOUSEEVENT);
tme.dwFlags = TME_LEAVE | TME_CANCEL;
tme.hwndTrack = hwnd;
//if(TrackMouseEvent(&tme)) PostMessage(hwnd, WM_MOUSELEAVE, 0, 0); //Commented this line out to do things a bit differently with the same results
if(TrackMouseEvent(&tme)) { //If this succeeds it means mouse tracking was canceled
bMouseTracking = FALSE;
InvalidateRect(hwnd, 0, TRUE);
}
////////all the way down to here the result is the same
//If you comment everything in this block out then you have another problem which can be tested with this condition:
//With window enabled move mouse over window, then press the ENTER key. The color should change
//from red to blue but it doesn't. It will change to blue though if you move the mouse 1 or more pixels after you've pressed the ENTER key
}
}
break;
case WM_DESTROY:
bMouseTracking = FALSE;
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
static HWND hChild;
switch(msg)
{
case WM_CREATE:
hChild = CreateWindowEx(0, g_szChildClassName, 0, WS_VISIBLE | WS_CHILD, 4, 4, 240, 80, hwnd, 0, g_hInst, 0);
break;
case WM_KEYDOWN:
if(wParam == VK_SPACE) EnableWindow(hChild, TRUE);
else if(wParam == VK_RETURN) EnableWindow(hChild, FALSE);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, int nCmdShow)
{
const TCHAR szClassName[] = L"abccccccc";
WNDCLASSEX wc;
HWND hwnd;
MSG msg;
SecureZeroMemory(&wc, sizeof(WNDCLASSEX));
wc.cbSize = sizeof(WNDCLASSEX);
wc.hbrBackground = (HBRUSH)(COLOR_BTNFACE + 1);
wc.hCursor = LoadCursor(0, IDC_ARROW);
wc.hIcon = LoadIcon(0, IDI_APPLICATION);
wc.hInstance = hInstance;
wc.lpfnWndProc = WndProc;
wc.lpszClassName = szClassName;
if(!RegisterClassEx(&wc)) return 0; //Register main window class
SecureZeroMemory(&wc, sizeof(WNDCLASSEX));
wc.cbSize = sizeof(WNDCLASSEX);
wc.hCursor = LoadCursor(0, IDC_ARROW);
wc.hInstance = hInstance;
wc.lpfnWndProc = ChildProc;
wc.lpszClassName = g_szChildClassName;
if(!RegisterClassEx(&wc)) return 0; //Register child window class
g_hInst = hInstance;
hwnd = CreateWindowEx(0, szClassName, L"Test", WS_OVERLAPPEDWINDOW, 40, 40, 420, 200, 0, 0, hInstance, 0);
if(!hwnd) return 0;
ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);
while(GetMessage(&msg, 0, 0, 0) > 0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int)msg.wParam;
}
EDIT: You can't see the cursor in the pictures cause I used screen capture and it doesn't capture the cursor. In the first picture the cursor is outside of the child window and in the second picture the cursor is inside of the child window
ENTER key pressed when cursor is outside of child window
SPACE key pressed after the ENTER key was previously pressed and cursor is hovering over child window

Answer 1

I don't know if this is a shortcoming of the documentation or a bug in TrackMouseEvent, but it looks like TrackMouseEvent doesn't expect to be called within your WM_ENABLE handler.
To avoid that, try posting a message from WM_ENABLE and calling TrackMouseEvent from that:
case WM_ENABLE:
PostMessage(hwnd, WM_USER, wParam, lParam);
break;
case WM_USER:
if(wParam)
{
RECT rc;
if(GetWindowRect(hwnd, &rc))
{
POINT pt;
if(GetCursorPos(&pt))
if(PtInRect(&rc, pt))
{
TRACKMOUSEEVENT tme = { 0 };
tme.cbSize = sizeof(TRACKMOUSEEVENT);
tme.dwFlags = TME_LEAVE;
tme.hwndTrack = hwnd;
//TrackMouseEvent() posts WM_MOUSELEAVE if conditions 1 and 2 are met, even though I'm trying to turn
//mouse tracking on and the cursor is over the child window. It doesn't make sense
//The problems is this piece of code right here /* bMouseTracking = TrackMouseEvent(&tme); */
//It should turn tracking on but it doesn't it cancels it even though WS_DISABLED has already been removed
//at this point
bMouseTracking = TrackMouseEvent(&tme);
InvalidateRect(hwnd, 0, TRUE);
}
}
} else {
if(bMouseTracking) {
////////If you comment everything from here ...
TRACKMOUSEEVENT tme = { 0 };
tme.cbSize = sizeof(TRACKMOUSEEVENT);
tme.dwFlags = TME_LEAVE | TME_CANCEL;
tme.hwndTrack = hwnd;
//if(TrackMouseEvent(&tme)) PostMessage(hwnd, WM_MOUSELEAVE, 0, 0); //Commented this line out to do things a bit differently with the same results
if(TrackMouseEvent(&tme)) { //If this succeeds it means mouse tracking was canceled
bMouseTracking = FALSE;
InvalidateRect(hwnd, 0, TRUE);
}
////////all the way down to here the result is the same
//If you comment everything in this block out then you have another problem which can be tested with this condition:
//With window enabled move mouse over window, then press the ENTER key. The color should change
//from red to blue but it doesn't. It will change to blue though if you move the mouse 1 or more pixels after you've pressed the ENTER key
}
}
break;