ELS window settings, WM_ CREATE、WM_ PAINT

#include<Windows.h>
#include"resource.h"
LRESULT CALLBACK PELouSi(HWND hWnd, UINT oMsg, WPARAM wParam, LPARAM lParam);
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPreInstance,LPSTR ipCmdLine,int nCmdShow)
{
    // Initialize window class .
    WNDCLASSEX  db;
    HWND hWnd;
    MSG msg;// Structural variable .

    db.cbClsExtra = 0;
    db.cbSize = sizeof(WNDCLASSEX);
    db.cbWndExtra = 0;

    db.hbrBackground = (HBRUSH)COLOR_BACKGROUND;// The background color .
    
    // Return value ： Handle of mouse .
    // Parameters 1： If the system cursor is loaded ,NULL、 If you load a custom cursor , Fill in the real column handle ,hInstance; Parameters 2： System cursor , Fill in the defined macro directly 、 If you load a custom cursor , Just use MAKEINTRESOURCE(240) Load the corresponding resources ID.
    //db.hCursor = LoadCursor(NULL,IDC_HAND);// Load the system defined cursor .
    db.hCursor = LoadCursor(hInstance,MAKEINTRESOURCE (IDC_NODROP));// Customized cursor . Resource file -> add to -> resources ->Cursor->IDC_NODROP-> newly build .
    
    // Return value ： Handle to icon .
    // Parameters 1： If the system cursor is loaded ,NULL、 If you load a custom cursor , Fill in the real column handle ,hInstance; Parameters 2： System cursor , Fill in the defined macro directly 、 If you load a custom cursor , Just use MAKEINTRESOURCE(240) Load the corresponding resources ID.
    //db.hIcon = LoadIcon(NULL,IDI_ASTERISK);// Load the system defined cursor .
    db.hIcon = LoadIcon(hInstance,MAKEINTRESOURCE(IDI_ICON1));// Status bar icons .
    
    //db.hIconSm = NULL;// The icon in the upper left corner is defined for this . If it is blank, it defaults to the status bar icon .
    db.hIconSm = LoadIcon(NULL,IDI_HAND);
    db.hInstance = hInstance;
    db.lpfnWndProc = PELouSi;// Callback function name .
    db.lpszClassName = "els";
    db.lpszMenuName = NULL;
    db.style = CS_HREDRAW | CS_VREDRAW;

    if(0==RegisterClassEx(&db))
    {
        int a = GetLastError();
        return 0;
    }

    // create a window .hWnd Window handle Failure to return NULL. 
    // Window style ： Parameters 4; Window name ： Parameters 3.
    hWnd=CreateWindowEx(WS_EX_TOPMOST,"els","els square ",WS_OVERLAPPEDWINDOW,100,100,500,500,NULL,NULL,hInstance,NULL);

    if (NULL == hWnd)// Window handle . Unique identification of the window .
    {

        return 0;
    }

    // Display window
    ShowWindow(hWnd, nCmdShow);
    
    // Message loop . queue .
    while(GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return 0;
}
    // Callback function
    // Return value ：LRESULT,CALLBACK Calling convention .
    // Parameters 1： Window handle ; Parameters 2： news ID.
LRESULT CALLBACK PELouSi(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam)// LRESULT:long type ;UINT： Unsigned integer , News ID.
{
    PAINTSTRUCT pt;// Defining structure .
    HDC hDc;
    // Close window message
    switch (nMsg)
    {
    case WM_CREATE:// The first message received by the window information handler , It is also the first message processed by the callback function ( by WM_CREATE). This message is generated only once , It is generally used to initialize some data .
        //GetLastError();// Optimize .
        break;

    // Is the second message processed by the callback function ( by WM_PAINT).
    // When a part of the display area of the window changes to （ Invalid ）, So much so that （ Update the screen ） when , The program will be notified by this message .
    // The last member of the window structure CS_HREDRAW|CS_VREDRAW, The purpose is when the window size changes , produce WM_PAINT news .
    // When windows overlap , When the overlap gradually appears .
    case WM_PAINT:
        //GetLastError();// Optimize .
        hDc=BeginPaint(hWnd,&pt);//getDC, Identification of window operable area .
        // Draw the contents of the window in between .

        EndPaint();// end .
        break;
    case WM_DESTROY:
            PostQuitMessage(0);// call PostQuitMessage(0) This function emits WM_QUIT news .// The point and fork system generates WM_CLOSE,WM_DESTROY,WM_QUIT.
            break;
        
    }// Manually handle the cross off message .

    return DefWindowProc(hWnd, nMsg, wParam, lParam);
    //LRESULT a=DefWindowProc(hWnd, oMsg, wParam, lParam);// function
    //return a;
}