scroll example

// Win32Project4.cpp : Defines the entry point for the application.
//

#include "stdafx.h"
#include "Win32Project4.h"
#include <strsafe.h>
#include <Commctrl.h>
#include <atltrace.h>

#define MAX_LOADSTRING 100

// Global Variables:
HINSTANCE hInst;                                // current instance
TCHAR szTitle[MAX_LOADSTRING];                  // The title bar text
TCHAR szWindowClass[MAX_LOADSTRING];            // the main window class name

// Forward declarations of functions included in this code module:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);
int g_scrollY = 0;

int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPTSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    // TODO: Place code here.
    MSG msg;
    HACCEL hAccelTable;

    // Initialize global strings
    LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
    LoadString(hInstance, IDC_WIN32PROJECT4, szWindowClass, MAX_LOADSTRING);
    MyRegisterClass(hInstance);

    // Perform application initialization:
    if (!InitInstance (hInstance, nCmdShow))
    {
        return FALSE;
    }

    hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WIN32PROJECT4));

    // Main message loop:
    while (GetMessage(&msg, NULL, 0, 0))
    {
        if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    return (int) msg.wParam;
}



//
//  FUNCTION: MyRegisterClass()
//
//  PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEX wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);

    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.cbClsExtra     = 0;
    wcex.cbWndExtra     = 0;
    wcex.hInstance      = hInstance;
    wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_WIN32PROJECT4));
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = MAKEINTRESOURCE(IDC_WIN32PROJECT4);
    wcex.lpszClassName  = szWindowClass;
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

    return RegisterClassEx(&wcex);
}

//
//   FUNCTION: InitInstance(HINSTANCE, int)
//
//   PURPOSE: Saves instance handle and creates main window
//
//   COMMENTS:
//
//        In this function, we save the instance handle in a global variable and
//        create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   HWND hWnd;

   hInst = hInstance; // Store instance handle in our global variable

   hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW | WS_VSCROLL,
      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);

   if (!hWnd)
   {
      return FALSE;
   }

   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

//
//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_COMMAND  - process the application menu
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    int wmId, wmEvent;
    PAINTSTRUCT ps;
    HDC hdc;

    switch (message)
    {
    case WM_COMMAND:
        wmId    = LOWORD(wParam);
        wmEvent = HIWORD(wParam);
        // Parse the menu selections:
        switch (wmId)
        {
        case IDM_ABOUT:
            DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
            break;
        case IDM_EXIT:
            DestroyWindow(hWnd);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
        }
        break;
    case WM_LBUTTONDOWN:
    {
        SCROLLINFO si = { 0 };
        si.cbSize = sizeof(SCROLLINFO);
        si.fMask = SIF_POS;
        si.nPos = 0;
        si.nTrackPos = 0;
        GetScrollInfo(hWnd, SB_VERT, &si);
        WCHAR buf[20];
        StringCchPrintf(buf, 20, L"pos = %d\n", si.nPos);
        OutputDebugString(buf);
        break;
    }
    case WM_VSCROLL:
    {
        auto action = LOWORD(wParam);
        HWND hScroll = (HWND)lParam;
        int pos = -1;
        if (action == SB_THUMBPOSITION || action == SB_THUMBTRACK) {
            pos = HIWORD(wParam);
        } else if (action == SB_LINEDOWN) {
            pos = g_scrollY + 30;
        } else if (action == SB_LINEUP) {
            pos = g_scrollY - 30;
        }
        if (pos == -1)
            break;
        WCHAR buf[20];
        SCROLLINFO si = { 0 };
        si.cbSize = sizeof(SCROLLINFO);
        si.fMask = SIF_POS;
        si.nPos = pos;
        si.nTrackPos = 0;
        SetScrollInfo(hWnd, SB_VERT, &si, true);
        GetScrollInfo(hWnd, SB_VERT, &si);
        pos = si.nPos;
        POINT pt;
        pt.x = 0;
        pt.y = pos - g_scrollY;
        auto hdc = GetDC(hWnd);
        LPtoDP(hdc, &pt, 1);
        ReleaseDC(hWnd, hdc);
        ScrollWindow(hWnd, 0, -pt.y, NULL, NULL);
        g_scrollY = pos;
        return 0;
    }
    case WM_CREATE:
    {
        for (int i = 0; i < 100; ++i) {
            auto hEdit = CreateWindowEx(WS_EX_CLIENTEDGE, L"EDIT", L"",
                WS_CHILD | WS_VISIBLE | ES_AUTOHSCROLL, 10, 30 * i, 250, 21, hWnd, NULL, hInst, NULL);
            wchar_t buf[10];
            StringCchPrintf(buf, 10, L"%d", i);
            SetWindowText(hEdit, buf);
        }
        RECT rc = { 0 };
        GetClientRect(hWnd, &rc);
        SCROLLINFO si = { 0 };
        si.cbSize = sizeof(SCROLLINFO);
        si.fMask = SIF_ALL;
        si.nMin = 0;
        si.nMax = 30 * 99 + 21;
        si.nPage = (rc.bottom - rc.top);
        si.nPos = 0;
        si.nTrackPos = 0;
        SetScrollInfo(hWnd, SB_VERT, &si, true);
        return 0;
    }
    case WM_SIZE:
    {
        RECT rc = { 0 };
        GetClientRect(hWnd, &rc);
        SCROLLINFO si = { 0 };
        si.cbSize = sizeof(SCROLLINFO);
        si.fMask = SIF_ALL;
        si.nMin = 0;
        si.nMax = 30 * 99 + 21;
        si.nPage = (rc.bottom - rc.top);
        si.nPos = 0;
        si.nTrackPos = 0;
        SetScrollInfo(hWnd, SB_VERT, &si, true);
        break;
    }
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);
        // TODO: Add any drawing code here...
        EndPaint(hWnd, &ps);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
    UNREFERENCED_PARAMETER(lParam);
    switch (message)
    {
    case WM_INITDIALOG:
        return (INT_PTR)TRUE;

    case WM_COMMAND:
        if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
        {
            EndDialog(hDlg, LOWORD(wParam));
            return (INT_PTR)TRUE;
        }
        break;
    }
    return (INT_PTR)FALSE;
}