中点画圆法

#include<Windows.h>
#include<iostream>
#include<cmath>
using namespace std;
const int ScreenWidth = 500;
const int ScreenHeight = 500;
LRESULT CALLBACK WinProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message) {
    case WM_CLOSE:
        DestroyWindow(hWnd);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
        break;
    }
    return 0;
}
void CirclePoints(HDC hdc, int x, int y,int offx,int offy)//利用对称性画整圆
{
    SetPixel(hdc, x + offx, y + offy, RGB(0, 0, 0));
    SetPixel(hdc, y + offx, x + offy, RGB(0, 0, 0));
    SetPixel(hdc, x + offx, -y + offy, RGB(0, 0, 0));
    SetPixel(hdc, -y + offx, x + offy, RGB(0, 0, 0));
    SetPixel(hdc, -x + offx, y + offy, RGB(0, 0, 0));
    SetPixel(hdc, y + offx, -x + offy, RGB(0, 0, 0));
    SetPixel(hdc, -x + offx, -y + offy, RGB(0, 0, 0));
    SetPixel(hdc, -y + offx, -x + offy, RGB(0, 0, 0));
}
void MidPointCircle(HDC hdc, int x1, int y1, int r)
{
    int x, y, e;
    x = 0; y = r; e = 1 - r;
    CirclePoints(hdc, x, y, x1, y1);
    while (x <= y)
    {
        if (e < 0)
            e += 2 * x + 3;
        else
        {
            e += 2 * (x - y) + 5;
            y--;
        }
        x++;
        CirclePoints(hdc, x, y, x1, y1);
    }
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int nShowCmd)
{
    WNDCLASS wcs;
    wcs.cbClsExtra = 0;                                         // 窗口类附加参数  
    wcs.cbWndExtra = 0;                                         // 窗口附加参数  
    wcs.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);    // 窗口DC背景  
    wcs.hCursor = LoadCursor(hInstance, IDC_CROSS);             // 鼠标样式  
    wcs.hIcon = LoadIcon(NULL, IDI_WINLOGO);                    // 窗口icon  
    wcs.hInstance = hInstance;                                  // 应用程序实例  
    wcs.lpfnWndProc = (WNDPROC)WinProc;
    wcs.lpszClassName = "CG";
    wcs.lpszMenuName = NULL;
    wcs.style = CS_VREDRAW | CS_HREDRAW;
    RegisterClass(&wcs);
    HWND hWnd;
    hWnd = CreateWindow("CG", "DrawCircle", WS_OVERLAPPEDWINDOW, 200, 200, ScreenWidth, ScreenHeight, NULL, NULL, hInstance, NULL);
    ShowWindow(hWnd, nShowCmd);
    UpdateWindow(hWnd);
    MSG msg;
    // hdc init
    HDC hdc = GetDC(hWnd);
    MidPointCircle(hdc, 200, 200, 150);
    // 消息循环  
    while (GetMessage(&msg, 0, NULL, NULL)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    // release
    ReleaseDC(hWnd, hdc);
    return 0;
}