How to detect drag in a mouse hook procedure - c++

Question

I've successfully set up a mouse hook for a window, and I'd like to detect a drag operation when the left mouse button is clicked. I've tried using DragDetect, as shown below, but it never returns TRUE, and it never suppresses the subsequent mouse-up event (in this code, hwnd is the target window):
LRESULT CALLBACK MouseHookProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if (nCode < 0)
{
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
switch (wParam)
{
case WM_LBUTTONDOWN:
{
// Get the click point
LPMOUSEHOOKSTRUCT pMouseHookStruct = reinterpret_cast<LPMOUSEHOOKSTRUCT>(lParam);
CPoint ptClick = pMouseHookStruct->pt;
// Drag detect
BOOL fDrag = DragDetect(hwnd, ptClick);
if (fDrag)
{
MessageBox(NULL, L"Drag", NULL, MB_OK);
}
break;
}
}
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
Does DragDetect not work within hook procedures, or am I just doing something wrong?

Answer 1

As comments pointed, DragDetect does not predict the future. But you can compare the POINT of WM_LBUTTONDOWN and WM_MOUSEMOVE in a click-time.
Sample:
#include <windows.h>
#include <iostream>
using namespace std;
typedef BOOL(*SETHOOK)(HWND hWnd);
typedef BOOL(*UNHOOK)();
LRESULT CALLBACK WndProcFunc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, message, wParam, lParam);
}
int main(int argc, char* argv[])
{
WNDCLASS wc{};
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = WndProcFunc;
wc.hInstance = GetModuleHandle(NULL);
wc.lpszClassName = L"Class_Name";
wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
RegisterClass(&wc);
HWND hWnd = CreateWindow(L"Class_Name", L"Test", WS_OVERLAPPEDWINDOW, 0, 0, 1000, 500, NULL, NULL, GetModuleHandle(NULL), NULL);
SETHOOK SetHook;
UNHOOK UnHook;
HMODULE h = LoadLibraryA("PATH\\DLL4.dll");
SetHook = (SETHOOK)GetProcAddress(h, "SetHook");
UnHook = (UNHOOK)GetProcAddress(h, "UnHook");
BOOL i = SetHook(hWnd);
ShowWindow(hWnd, 1);
UpdateWindow(hWnd);
MSG Msg;
while (GetMessage(&Msg, NULL, 0, 0))
{
TranslateMessage(&Msg);
DispatchMessage(&Msg);
}
UnHook();
return 0;
}
DLL:
// dllmain.cpp : Defines the entry point for the DLL application.
#include "pch.h"
#include <windows.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#define PRESS TRUE
#define RELEASE FALSE
HHOOK tHook;
HMODULE hinstDLL;
BOOL button = RELEASE;
BOOL Drag = FALSE;
HWND hWnd;
POINT pt = { 0 };
LRESULT CALLBACK MouseProc(int nCode, WPARAM wParam, LPARAM lParam) {
if (nCode < 0)
{
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
LPMOUSEHOOKSTRUCT pMouseHookStruct = reinterpret_cast<LPMOUSEHOOKSTRUCT>(lParam);
if (pMouseHookStruct->hwnd != hWnd)
{
button = RELEASE;
Drag = FALSE;
}
else {
switch (wParam)
{
case WM_LBUTTONDOWN:
{
button = PRESS;
Drag = FALSE;
printf("WM_LBUTTONDOWN\n");
printf("%d , %d\n", pMouseHookStruct->pt.x, pMouseHookStruct->pt.y);
pt.x = pMouseHookStruct->pt.x;
pt.y = pMouseHookStruct->pt.y;
break;
}
case WM_LBUTTONUP:
{
button = RELEASE;
Drag = FALSE;
printf("WM_LBUTTONUP\n");
break;
}
case WM_MOUSEMOVE:
{
if (button == PRESS)
{
printf("%d , %d\n", pMouseHookStruct->pt.x, pMouseHookStruct->pt.y);
if (Drag == FALSE && (abs(pt.x - pMouseHookStruct->pt.x) >= GetSystemMetrics(SM_CXDRAG) || abs(pt.y - pMouseHookStruct->pt.y) >= GetSystemMetrics(SM_CYDRAG)))
{
printf("Drag\n");
Drag = TRUE;
}
}
break;
}
}
}
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
extern "C" __declspec(dllexport) BOOL SetHook(HWND hwnd)
{
hWnd = hwnd;
tHook = SetWindowsHookEx(WH_MOUSE, MouseProc, hinstDLL, 0);
if (tHook == NULL)
return FALSE;
else
return TRUE;
}
extern "C" __declspec(dllexport) BOOL UnHook()
{
return UnhookWindowsHookEx(tHook);
}
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
hinstDLL = hModule;
break;
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}