中点画圆算法的实现

    算法来源于Donald Hearn和M. Pauline Baker合著的神作《计算机图形学》。程序在codeblocks下采用win32 api编程实现。

#include <windows.h>#include <math.h>/*  Declare Windows procedure  */LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);float Radius (POINT ptBeg, POINT ptEnd);void CircleMidpoint (HDC hdc, int xc, int yc, int rad);void CirclePlotPoints (HDC hdc, int xc, int yc, POINT circPt);void DrawCircle (HDC hdc, POINT ptBeg, POINT ptEnd);static int radius;/*  Make the class name into a global variable  */char szClassName[ ] = "CodeBlocksWindowsApp";int WINAPI WinMain (HINSTANCE hThisInstance,                     HINSTANCE hPrevInstance,                     LPSTR lpszArgument,                     int nCmdShow){    HWND hwnd;               /* This is the handle for our window */    MSG messages;            /* Here messages to the application are saved */    WNDCLASSEX wincl;        /* Data structure for the windowclass */    /* The Window structure */    wincl.hInstance = hThisInstance;    wincl.lpszClassName = szClassName;    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */    wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */    wincl.cbSize = sizeof (WNDCLASSEX);    /* Use default icon and mouse-pointer */    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);    wincl.lpszMenuName = NULL;                 /* No menu */    wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */    wincl.cbWndExtra = 0;                      /* structure or the window instance */    /* Use Windows's default colour as the background of the window */    wincl.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);    /* Register the window class, and if it fails quit the program */    if (!RegisterClassEx (&wincl))        return 0;    /* The class is registered, let's create the program*/    hwnd = CreateWindowEx (           0,                   /* Extended possibilites for variation */           szClassName,         /* Classname */           "Code::Blocks Template Windows App",       /* Title Text */           WS_OVERLAPPEDWINDOW, /* default window */           CW_USEDEFAULT,       /* Windows decides the position */           CW_USEDEFAULT,       /* where the window ends up on the screen */           544,                 /* The programs width */           375,                 /* and height in pixels */           HWND_DESKTOP,        /* The window is a child-window to desktop */           NULL,                /* No menu */           hThisInstance,       /* Program Instance handler */           NULL                 /* No Window Creation data */           );    /* Make the window visible on the screen */    ShowWindow (hwnd, nCmdShow);    /* Run the message loop. It will run until GetMessage() returns 0 */    while (GetMessage (&messages, NULL, 0, 0))    {        /* Translate virtual-key messages into character messages */        TranslateMessage(&messages);        /* Send message to WindowProcedure */        DispatchMessage(&messages);    }    /* The program return-value is 0 - The value that PostQuitMessage() gave */    return messages.wParam;}/*  This function is called by the Windows function DispatchMessage()  */LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){    static POINT ptBeg, ptEnd;    HDC hdc;    PAINTSTRUCT ps;    switch (message)                  /* handle the messages */    {        case WM_CREATE:            radius = 0;            break;        case WM_LBUTTONDOWN:            ptBeg.x = LOWORD (lParam);            ptBeg.y = HIWORD (lParam);            ptEnd = ptBeg;            InvalidateRect (hwnd, NULL, TRUE);            break;        case WM_MOUSEMOVE:            if (wParam & MK_LBUTTON)            {                hdc = GetDC (hwnd);                SelectObject (hdc, GetStockObject (BLACK_PEN));                SetROP2 (hdc, R2_NOTXORPEN);                DrawCircle (hdc, ptBeg, ptEnd);                ptEnd.x = LOWORD (lParam);                ptEnd.y = HIWORD (lParam);                DrawCircle (hdc, ptBeg, ptEnd);                ReleaseDC (hwnd, hdc);            }            break;        case WM_LBUTTONUP:                InvalidateRect (hwnd, NULL, TRUE);                break;        case WM_PAINT:            hdc = BeginPaint(hwnd, &ps);            if(ptEnd.x != ptBeg.x || ptEnd.y != ptEnd.y)            {                SelectObject(hdc, GetStockObject(BLACK_PEN));                CircleMidpoint(hdc, ptBeg.x, ptBeg.y, radius);            }            EndPaint(hwnd, &ps);            break;        case WM_DESTROY:            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */            break;        default:                      /* for messages that we don't deal with */            return DefWindowProc (hwnd, message, wParam, lParam);    }    return 0;}float Radius(POINT ptBeg, POINT ptEnd){    return sqrt ((ptEnd.x - ptBeg.x)*(ptEnd.x - ptBeg.x) + (ptEnd.y - ptBeg.y)*(ptEnd.y - ptBeg.y));}void CircleMidpoint (HDC hdc, int xc, int yc, int rad){    POINT circPt;    int p = 1 - rad;    circPt.x = 0;    circPt.y = rad;    CirclePlotPoints (hdc, xc, yc, circPt);    while (circPt.x < circPt.y)    {        circPt.x++;        if (p < 0)        {            p += 2*circPt.x + 1;        }        else        {            circPt.y--;            p += 2*circPt.x + 1 - 2*circPt.y;        }        CirclePlotPoints (hdc, xc, yc, circPt);    }}void CirclePlotPoints (HDC hdc, int xc, int yc, POINT circPt){    SetPixel (hdc, xc + circPt.x, yc + circPt.y, 0);    SetPixel (hdc, xc - circPt.x, yc + circPt.y, 0);    SetPixel (hdc, xc + circPt.x, yc - circPt.y, 0);    SetPixel (hdc, xc - circPt.x, yc -circPt.y, 0);    SetPixel (hdc, xc + circPt.y, yc + circPt.x, 0);    SetPixel (hdc, xc -circPt.y, yc + circPt.x, 0);    SetPixel (hdc, xc + circPt.y, yc - circPt.x, 0);    SetPixel (hdc, xc - circPt.y, yc - circPt.x, 0);}void DrawCircle(HDC hdc, POINT ptBeg, POINT ptEnd){    radius = Radius (ptBeg, ptEnd);    MoveToEx (hdc, ptBeg.x, ptBeg.y, NULL);    LineTo (hdc, ptEnd.x, ptEnd.y);    CircleMidpoint (hdc, ptBeg.x, ptBeg.y, radius);}