Mouse Wheel Scroll Example

#include <windows.h>
#include <tchar.h>

#define WM_MOUSEWHEEL 0x020A    // For older Visual C++

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int scrollPosition = 0;

int WINAPI WinMain(HINSTANCE hInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine,
                   int nCmdShow)
{
    WNDCLASS wc;
    MSG msg;

    wc.style         = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = TEXT("ScrollDemo");

    RegisterClass(&wc);

    HWND hwnd = CreateWindow(
        TEXT("ScrollDemo"),
        TEXT("Mouse Wheel Scrolling Demo"),
        WS_OVERLAPPEDWINDOW,
        100,
        100,
        400,
        300,
        NULL,
        NULL,
        hInstance,
        NULL);

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    while(GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}


LRESULT CALLBACK WndProc(HWND hwnd,
                         UINT message,
                         WPARAM wParam,
                         LPARAM lParam)
{
    PAINTSTRUCT ps;
    HDC hdc;
    TCHAR text[100];
    int i;

    switch(message)
    {
        case WM_MOUSEWHEEL:

            if((short)HIWORD(wParam) > 0)
                scrollPosition -= 20;
            else
                scrollPosition += 20;

            // Limit scrolling range
            if(scrollPosition < 0)
                scrollPosition = 0;

            if(scrollPosition > 600)
                scrollPosition = 600;

            InvalidateRect(hwnd, NULL, TRUE);
            return 0;


        case WM_PAINT:

            hdc = BeginPaint(hwnd, &ps);

            for(i = 0; i < 40; i++)
            {
                wsprintf(text,
                         TEXT("This is line number %d"),
                         i + 1);

                TextOut(hdc,
                        50,
                        (i * 25) - scrollPosition,
                        text,
                        lstrlen(text));
            }

            EndPaint(hwnd, &ps);
            return 0;


        case WM_DESTROY:

            PostQuitMessage(0);
            return 0;
    }

    return DefWindowProc(hwnd, message, wParam, lParam);
}