Drawing a Circle with Mid – Point Circle Algorithm in C/C++

As in the previous line drawing algorithm, we sample at unit intervals and determine the closest pixel position to the specified circle path at each step. For a given radius r and screen center position (xc, yc), we can first set up our algorithm to calculate pixel positions around a circle path centered at the coordinate origin (0, 0). Then each calculated  position (x, y) is moved to its proper screen position by adding xc to x and yc to y. Along the circle section from x = 0 to x = y in the first quadrant, the slope of the curve varies from 0 to –1.  Therefore, we can take unit steps in the positive x direction over this octant and use a decision parameter to determine which of the two possible y positions is closer to the circle path at each step. Position in the other seven octants are then obtained by symmetry.

The following section implements Mid – Point Cicle  Algorithm in C/C++. The source code is complied using gcc Compiler and Code::Blocks IDE. To print a pixel, SetPixel() function of windows.h is used.

Note: to run this code in your machine with Code::blocks IDE, add a link library libgdi32.a (it is usually inside MinGW\lib )  in linker setting.
Souce Code

#include <windows.h>
#include <cmath>
#define ROUND(a) ((int) (a + 0.5))
/* set window handle */
static HWND sHwnd;
static COLORREF redColor=RGB(255,0,0);
static COLORREF blueColor=RGB(0,0,255);
static COLORREF greenColor=RGB(0,255,0);
void SetWindowHandle(HWND hwnd){
    sHwnd=hwnd;
}
/* SetPixel */
void setPixel(int x,int y,COLORREF& color=redColor){
    if(sHwnd==NULL){
        MessageBox(NULL,"sHwnd was not initialized !","Error",MB_OK|MB_ICONERROR);
        exit(0);
    }
    HDC hdc=GetDC(sHwnd);
    SetPixel(hdc,x,y,color);
    ReleaseDC(sHwnd,hdc);
    return;
}
void circlePoints(int xCenter, int yCenter, int x, int y){
    setPixel(xCenter + x, yCenter + y);
    setPixel(xCenter - x, yCenter + y);
    setPixel(xCenter + x, yCenter - y);
    setPixel(xCenter - x, yCenter - y);
    setPixel(xCenter + y, yCenter + x);
    setPixel(xCenter - y, yCenter + x);
    setPixel(xCenter + y, yCenter - x);
    setPixel(xCenter - y, yCenter - x);
}
void drawCircle(int xCenter, int yCenter, int radius){
    int x = 0;
    int y = radius;
    int p = 1 - radius;
    circlePoints(xCenter, yCenter, x, y);
    while(x < y){
        x++;
        if (p < 0){
            p += 2 * x + 1;
        }else{
            y--;
            p += 2 * (x - y) + 1;
        }
        circlePoints(xCenter, yCenter, x, y);
    }
}
/* Window Procedure WndProc */
LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam){
    switch(message){
        case WM_PAINT:
            SetWindowHandle(hwnd);
            drawCircle(200, 200, 100);
            break;
        case WM_CLOSE: // FAIL THROUGH to call DefWindowProc
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
        default:
        break; // FAIL to call DefWindowProc //
    }
    return DefWindowProc(hwnd,message,wParam,lParam);
}
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int iCmdShow){
    static TCHAR szAppName[] = TEXT("Circle");
    WNDCLASS wndclass;
    wndclass.style         = CS_HREDRAW|CS_VREDRAW ;
    wndclass.lpfnWndProc   = WndProc ;
    wndclass.cbClsExtra    = 0 ;
    wndclass.cbWndExtra    = 0 ;
    wndclass.hInstance     = hInstance ;
    wndclass.hIcon         = LoadIcon (NULL, IDI_APPLICATION) ;
    wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
    wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
    wndclass.lpszMenuName  = NULL ;
    wndclass.lpszClassName = szAppName ;
    // Register the window //
    if(!RegisterClass(&wndclass)){
        MessageBox(NULL,"Registering the class failled","Error",MB_OK|MB_ICONERROR);
        exit(0);
    }
    // CreateWindow //
    HWND hwnd=CreateWindow(szAppName,"Mid Point Circle Drawing - Programming Techniques",
                WS_OVERLAPPEDWINDOW,
                 CW_USEDEFAULT,
                 CW_USEDEFAULT,
                 CW_USEDEFAULT,
                 CW_USEDEFAULT,
                 NULL,
                 NULL,
                 hInstance,
                 NULL);
    if(!hwnd){
        MessageBox(NULL,"Window Creation Failed!","Error",MB_OK);
        exit(0);
    }
    // ShowWindow and UpdateWindow //
    ShowWindow(hwnd,iCmdShow);
    UpdateWindow(hwnd);
    // Message Loop //
    MSG msg;
    while(GetMessage(&msg,NULL,0,0)){
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    /* return no error to the operating system */
    return 0;
}

Output