中點畫圓算法的實現

    算法來源於Donald Hearn和M. Pauline Baker合著的神作《計算機圖形學》。程序在codeblocks下采用win32 api編程實現。

#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);
}