Windows GDI：在for循环中调用draw函数

Question

这是我程序的主要功能。此代码有效，但是如果我将包含许多If和LineTo()调用的2 MoveToEx()个语句放在For循环中，那么屏幕上就不会显示图形输出。我尝试将GetDC()和ReleaseDC()调用放在For循环内，但没有做任何更改。请帮忙。抱歉，格式化是如此混乱。它通过3个不同的文本编辑器和一个Web浏览器。

    //  includes
    #include <stdafx.h>
    #include <windows.h>
    #include <windowsx.h>
    #include <string>
    #include <vector>

    //  namespaces
    using std::string;
    using std::vector;

    //  defines
    #define STARTX 1280/2
    #define STARTY 720/2
    #define CLIENT_WIDTH 1280
    #define CLIENT_HEIGHT 720
    #define SEGMENT_LENGTH 5
    #define SEGMENT_WIDTH 5
    #define KEY_DOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0)

    //  globals
    string szinput("sl");
    int iterations=2; int direction=1;  


    int WINAPI WinMain(HINSTANCE hinstance, HINSTANCE hprevinstance,
    LPSTR lpcmdline, int ncmdshow)
    {
HWND hwnd;
MSG msg;
WNDCLASSEX wc;
HDC hdc;

ZeroMemory(&wc, sizeof(WNDCLASSEX));

wc.cbSize=sizeof(WNDCLASSEX);
wc.style=CS_HREDRAW|CS_VREDRAW;
wc.lpfnWndProc=WindowProc;
wc.hInstance=hinstance;
wc.hCursor=LoadCursor(NULL, IDC_ARROW);
wc.lpszClassName=L"Fractals";

if(!RegisterClassEx(&wc))
{
    return(0);
}

if(!(hwnd=CreateWindow(L"Fractals", L"Fractals",
WS_OVERLAPPEDWINDOW|WS_VISIBLE, 0, 0, CLIENT_WIDTH,
CLIENT_HEIGHT, NULL, NULL, hinstance, NULL)))
{
    return(0);
}


//  main game loop

HPEN pen=CreatePen(PS_SOLID, SEGMENT_WIDTH, RGB(0, 255, 0));
POINT point;
//int center=CLIENT_WIDTH/CLIENT_HEIGHT;
int offsetx=10, offsety=10;
int x=STARTX, y=STARTY;
int flag=0;
int temp;

//while(TRUE)
//{
    while(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    if(msg.message==WM_QUIT)
    {
        //break;
    }
    hdc=GetDC(hwnd);
    SelectObject(hdc, pen);
    //  place the pen on the starting point specified by user
    //if(!flag)
    //{
    //SelectObject(hdc, pen);
    MoveToEx(hdc, STARTX, STARTY, &point);
    x=STARTX;
    y=STARTY;
    //flag=1;
    //}

vector<int> result=fngetParse();
//for(int i=iterations; i<iterations; i++)
//{
    //hdc=GetDC(hwnd);
//  if(!flag)
//  {
//      SelectObject(hdc, pen);
//      MoveToEx(hdc, STARTX, STARTY, &point);
//      x=STARTX;
//      y=STARTY;
//      flag=1;
//  }
//  SelectObject(hdc, pen);
    temp=result.at(0);
    if(temp==0)
    {
        if(direction==1)    //  flat
        {
            x+=10; y+=0;
            LineTo(hdc, x, y);
            direction=1;
            MoveToEx(hdc, x, y, &point);
        } else if(direction==2)
        {
            x+=10; y-=10;
            LineTo(hdc, x, y);
            direction=2;
            MoveToEx(hdc, x, y, &point);
        } else if(direction==3)
        {
            x+=0; y-=10;
            LineTo(hdc, x, y);
            direction=3;
            MoveToEx(hdc, x, y, &point);
        } else if(direction==4)
        {
            x-=10; y+=10;
            LineTo(hdc, x, y);
            direction=4;
            MoveToEx(hdc, x, y, &point);
        }
    }
    ////////////////
    temp=result.at(1);
    if(temp==1)
    {
        if(direction==1)    //  if 1, change to 2
        {
            x+=10; y-=10;
            LineTo(hdc, x, y);
            direction=2;
            MoveToEx(hdc, x, y, &point);
        } else if(direction==2) //  if 2, chnage to 3
        {
            x+=0; y-=10;
            LineTo(hdc, x, y);
            direction=3;
        } else if(direction==3) //  if 3, change to 4
        {
            x-=0; y-=10;
            LineTo(hdc, x, y);
            direction=4;
            MoveToEx(hdc, x, y, &point);
        } else if(direction==4) //  if 4 change to 1
        {
            x-=0; y+=10;
            LineTo(hdc, x, y);
            direction=1;
            MoveToEx(hdc, x, y, &point);
        }
    }
    //ReleaseDC(hwnd, hdc);
//}

    /*
    //  draw a straight line in the left direction
    //x+=25; y+=0;
    x+=10; y+=0;
    LineTo(hdc, x, y);
    //SelectObject(hdc, pen);
    MoveToEx(hdc, x, y, &point);

    //SelectObject(hdc, pen);
    //x=point.x; y=point.y;
    x+=10; y-=10;
    LineTo(hdc, x, y);
    //SelectObject(hdc, pen);
    MoveToEx(hdc, x, y, &point);
    //x+=25; y+=0;
    //LineTo(hdc, x, y);
    //SelectObject(hdc, pen);
    x+=10; y+=10;
    LineTo(hdc, x, y);
    MoveToEx(hdc, x, y, &point);

    x-=10; y+=10;
    LineTo(hdc, x, y);
    MoveToEx(hdc, x, y, &point);
    //  draw line at 45 degree angle
    //SelectObject(hdc, pen);
    //x+=25*cos(PI/2); y+=25*cos(PI/2);
    //x+=50; y-=20;
    //LineTo(hdc, x, y);
    //SelectObject(hdc, pen);
    //MoveToEx(hdc, x, y, &point);
    //
    //vector<int> result=fngetParse();
    //for(int i=0; i<result.size(); i++) {
    //  if(result.at(i)==0)
    //  {
    //      LineTo(hdc, x, y);
    //  }
    //  else if(result.at(i)==1)
    //  {
    //      LineTo(hdc, x+10*cos(PI/2), y+10*cos(PI/2));
    //  }

    //  MoveToEx(hdc, x, y, &point);
    //  x=+10; y+=10;
        //LineTo(hdc, 700, 400);
    //}
    */
    if(KEY_DOWN(VK_ESCAPE))
    {
        PostQuitMessage(0);
    }

    ReleaseDC(hwnd, hdc);
    Sleep(3000);
//}
return(msg.wParam);
    }

    vector<int> fnparseLSys(string& str)
    {
        vector<int> result;
        for(int i=0; i<str.length(); i++)
        {
    if(str.at(i)=='s')
    {
        result.push_back(0);
    } else if(str.at(i)=='l')
    {
        result.push_back(1);
    }
}

return result;
    }

    vector<int> fngetParse(void)
    {
vector<int> result;

result=fnparseLSys(szinput);
return result;
    }