Improve Zooming with Enhanced Mouse Wheels

// MouseWheel.cpp :

#include "stdafx.h"

HHOOK g_hHook = 0 ;
HANDLE g_hThread = 0 ;
bool g_bSkip = false ;
LONG g_nTotalDelta = 0 ;
bool g_bExit = false;

// parameters for SetParameters (and their defaults)
int g_nDelta = WHEEL_DELTA ;
int g_nSleep = 18 ; // 18 milliseconds seems to be the minimum value that can be processed.
int g_nEvents = 1 ; // 18 milliseconds seems to be the minimum value that can be processed.

__declspec( dllexport ) void SetParameters(int x1, int x2, int x3)
{
	//SuspendThread(g_hThread) ;
	g_bSkip = true ;
	g_nDelta = x1 ;
	g_nSleep = x2 ;
	g_nEvents=x3 ;
	g_bSkip = false ;
	//ResumeThread(g_hThread) ;
}

DWORD WINAPI WorkerThread(LPVOID pParam)
{
	while (!g_bExit) {
		if (g_bSkip) {
			Sleep(3) ;
			continue ;
		}
		if (g_nTotalDelta == 0) {
			Sleep(3) ;
			continue ;
		}
		int nDirection = g_nTotalDelta/abs(g_nTotalDelta) ; 
		mouse_event( MOUSEEVENTF_WHEEL, 0, 0, nDirection*g_nDelta, 0);
		Sleep(g_nSleep) ;
	}
	return 0 ;
}

LRESULT WINAPI ProcMouseLL (int nCode, WPARAM wParam, LPARAM lParam)
{
	if (nCode < 0)
		return CallNextHookEx ( g_hHook, nCode, wParam, lParam );
	if (WM_MOUSEWHEEL == wParam) {
		if (lParam == 0)
			return CallNextHookEx ( g_hHook, nCode, wParam, lParam );
		MSLLHOOKSTRUCT *hookStruct = (MSLLHOOKSTRUCT *)lParam ;
		short delta = (short)HIWORD(hookStruct->mouseData) ;
		if (hookStruct->flags & LLMHF_INJECTED) {
			// created by mouse_event()
			// assumption is that we called it from our WorkerThread
			if ((g_nTotalDelta*delta) > 0) {
				g_nTotalDelta -= delta ;
				if ((g_nTotalDelta*delta) < 0) {
					g_nTotalDelta = 0 ;
				}
				return CallNextHookEx ( g_hHook, nCode, wParam, lParam ); // pass mouse wheel to system and application
			}
			else {
				// we've reversed directions and discard mouse_event() going in the opposite direction
				return -1 ; // eat mouse wheel
			}
		}
		else {
			// physical hardware generated event
			g_nTotalDelta = abs(delta)/delta*g_nDelta*g_nEvents ;
			return -1 ; // eat mouse wheel
		}
	}
	if ((WM_LBUTTONDOWN == wParam) ||
	    (WM_LBUTTONUP == wParam) ||
		(WM_RBUTTONDOWN == wParam) ||
		(WM_RBUTTONUP == wParam)) {
			g_nTotalDelta=0 ;
	}
	return CallNextHookEx ( g_hHook, nCode, wParam, lParam );
}

BOOL WINAPI DllMain(
    HINSTANCE hinstDLL,
    DWORD fdwReason,
    LPVOID lpvReserved)
{
    if ( fdwReason == DLL_PROCESS_ATTACH )
    {
		DisableThreadLibraryCalls( hinstDLL );
        if ( g_hHook )
            return FALSE;
        g_hHook = SetWindowsHookEx( WH_MOUSE_LL, (HOOKPROC)ProcMouseLL,hinstDLL, 0 );
		DWORD threadid;
		g_bExit = false ;
		g_bSkip = true ;
		g_hThread = CreateThread(NULL, 0,  WorkerThread, 0, 0, &threadid);
	}
    else if ( fdwReason == DLL_PROCESS_DETACH )
    {
		g_bSkip = false ;
		g_bExit = true ;
		Sleep((DWORD)(g_nSleep+5)) ;
		if (g_hHook)     
		{                                       
			UnhookWindowsHookEx(g_hHook);     
			g_hHook = 0;
		}
    }
    return TRUE;
}

extern "C" BOOL __stdcall _DllMainCRTStartup( 
    HINSTANCE hinstDLL,
    DWORD fdwReason,
    LPVOID lpvReserved)
{
    return DllMain( hinstDLL, fdwReason, lpvReserved );
}