将位图渲染到控件里

需要知道GetDC与BeginPaint的区别，这里有一篇不错的文章。

简洁的就是说：BeginPaint() 和EndPaint() 可以删除消息队列中的WM_PAINT消息，并使无效区域有效。 
                         GetDC()和ReleaseDC()并不删除也不能使无效区域有效，因此当程序跳出 WM_PAINT 时 ，无效区域仍然存在。系统就回不断发送WM_PAINT消息，于是程序不断处理WM_PAINT消息。

如果用GetDC的话，窗口会一直在重绘，可以在WM_PAINT消息里加上断点即可知道

那么如何将位图渲染到控件里呢，我们需要用到DefSubclassProc(hwnd, uMsg, wParam, lParam);

这是默认的消息处理函数，因为是用来子类控件的消息事件，所以是DefSubclassProc。

在子类回调函数里的WM_PAINT添加DefSubclassProc即可。

下面的完整代码；

// WindowsProject49.cpp : Defines the entry point for the application.
//

#include "stdafx.h"
#include "WindowsProject49.h"
#include <Richedit.h>
#include <commctrl.h>

#pragma comment(lib, "comctl32.lib")

#define MAX_LOADSTRING 100
#define EDIT_CLASS RICHEDIT_CLASS
#define mb_err(x) MessageBox(NULL, TEXT(x), TEXT("Error!"), MB_ICONEXCLAMATION | MB_OK)
#define main_edit 101

// Global Variables:
HINSTANCE hInst;                                // current instance
WCHAR szTitle[MAX_LOADSTRING];                  // The title bar text
WCHAR szWindowClass[MAX_LOADSTRING] = L"Sample Window Class";            // the main window class name

HWND hedit = NULL;
HBITMAP hBitmap = NULL;

// 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);
LRESULT CALLBACK main_edit_proc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData);


int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPWSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    // TODO: Place code here.

    // Initialize global strings
    LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
    LoadStringW(hInstance, IDC_WINDOWSPROJECT49, szWindowClass, MAX_LOADSTRING);
    MyRegisterClass(hInstance);

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

    HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WINDOWSPROJECT49));

    MSG msg;

    // Main message loop:
    while (GetMessage(&msg, nullptr, 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)
{
    WNDCLASSEXW 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(NULL, IDI_APPLICATION);
    wcex.hCursor        = LoadCursor(nullptr, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName  = szWindowClass;
    wcex.hIconSm        = LoadIcon(NULL, IDI_APPLICATION);

    return RegisterClassExW(&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)
{
   hInst = hInstance; // Store instance handle in our global variable

   HWND hWnd = CreateWindowEx(
       0,                              // Optional window styles.
       szWindowClass,                     // Window class
       L"Learn to Program Windows",    // Window text
       WS_OVERLAPPEDWINDOW,            // Window style

       // Size and position
       CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

       NULL,       // Parent window    
       NULL,       // Menu
       hInstance,  // Instance handle
       NULL        // Additional application data
   );

   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)
{
    switch (message)
    {
    case WM_CREATE:
    {
        hBitmap = (HBITMAP)LoadImage(GetModuleHandle(NULL), L"C:\\Users\\strives\\Desktop\\small.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);

        LoadLibrary(L"Riched20.dll");
        hedit = CreateWindowEx(0, EDIT_CLASS, NULL,
            WS_CHILD | WS_VISIBLE | ES_MULTILINE
            | ES_AUTOVSCROLL | ES_AUTOHSCROLL | WS_HSCROLL,
            0, 0, 100, 100,
            hWnd, NULL, GetModuleHandle(NULL), NULL);
        if (main_edit_proc != NULL)
            SetWindowSubclass(hedit, main_edit_proc, main_edit, 1);

        if (hedit == NULL)
            mb_err("Could not create edit control.");
        else {
            SendMessage(hedit, EM_SETBKGNDCOLOR, 0, RGB(40, 40, 40));

            CHARFORMAT2 format;
            memset(&format, 0, sizeof format);

            format.cbSize = sizeof(CHARFORMAT2);
            format.dwMask = CFM_COLOR | CFM_FACE;
            format.crTextColor = RGB(255, 0, 255);
            memcpy(format.szFaceName, L"Consolas", sizeof(L"Consolas"));
            if (SendMessage(hedit, EM_SETCHARFORMAT, SCF_DEFAULT, (LPARAM)&format) == 0) {
                mb_err("Failed to set font.");
            }

            

            if (SendMessage(hedit, EM_SETTEXTMODE, TM_PLAINTEXT, 0) != 0) {
                mb_err("EM_SETTEXTMODE returned non-zero value");
            }

            //did not set the yHeight, so need to get it (from default)
            SendMessage(hedit, EM_GETCHARFORMAT, NULL, (LPARAM)&format);
            RECT rect;
            SendMessage(hedit, EM_GETRECT, 0, (LPARAM)&rect);
            rect.left = format.yHeight / 4;
            SendMessage(hedit, EM_SETRECT, 0, (LPARAM)&rect);
        }

        break;
    }
    case WM_COMMAND:
        {
            int wmId = LOWORD(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_PAINT:
    {
        PAINTSTRUCT     ps;
        HDC             hdc;
        BITMAP          bitmap;
        HDC             hdcMem;
        HGDIOBJ         oldBitmap;

        hdc = BeginPaint(hWnd, &ps);
        if (hdc == NULL) __debugbreak();

        hdcMem = CreateCompatibleDC(hdc);
        oldBitmap = SelectObject(hdcMem, hBitmap);

        GetObject(hBitmap, sizeof(bitmap), &bitmap);
        BitBlt(hdc, 200, 200, bitmap.bmWidth, bitmap.bmHeight, hdcMem, 0, 0, SRCCOPY);

        SelectObject(hdcMem, oldBitmap);
        DeleteDC(hdcMem);

        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;
}

LRESULT CALLBACK main_edit_proc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData) {
    switch (uMsg) {
    

    case WM_SETCURSOR:
    {
        POINT pos;

        GetCursorPos(&pos);
        HWND cur_hwnd = WindowFromPoint(pos);

        if (cur_hwnd == hwnd) SetCursor(LoadCursor(NULL, IDC_ARROW));
        else SendMessage(cur_hwnd, WM_SETCURSOR, 0, 0);

        return 0;
    }
    
    case WM_PAINT:
    {
        DefSubclassProc(hwnd, uMsg, wParam, lParam);
        HDC             hdc;
        BITMAP          bitmap;
        HDC             hdcMem;
        HGDIOBJ         oldBitmap;

        hdc = GetDC(hwnd);
        if (hdc == NULL) __debugbreak();

        hdcMem = CreateCompatibleDC(hdc);
        oldBitmap = SelectObject(hdcMem, hBitmap);

        GetObject(hBitmap, sizeof(bitmap), &bitmap);
        BitBlt(hdc, 0, 0, bitmap.bmWidth, bitmap.bmHeight, hdcMem, 0, 0, SRCCOPY);

        SelectObject(hdcMem, oldBitmap);
        DeleteDC(hdcMem);

        ReleaseDC(hwnd, hdc);
        return 0;
    }
    case WM_NCDESTROY:
        RemoveWindowSubclass(hwnd, &main_edit_proc, main_edit);
        break;
    

    }

    return DefSubclassProc(hwnd, uMsg, wParam, lParam);
}

效果：