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Liang-Barsky Line Clipping Algorithm in C

Program:
#include <windows.h>
#include <cmath>
#define ROUND(a) ((int) (a + 0.5))

static HWND sHwnd;
static COLORREF redColor=RGB(255,0,0);
static COLORREF blueColor=RGB(0,0,255);
static COLORREF greenColor=RGB(0,255,0);

typedef struct Point
{
    int x;
    int y;
}pt;

pt winMin = {100, 100};
pt winMax = {800, 400};
pt p1 = {50, 200};
pt p2 = {900, 300};

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 LineBresenham (int xa, int ya, int xb, int yb){
    int dx = (xb - xa), dy = (yb - ya);
    int x, y, xEnd, yEnd;
    int p = 2 * abs(dy) - abs(dx);
    int twoDy = 2 * abs(dy), twoDyDx = 2 * (abs(dy) - abs(dx));
    int tFactor = dx*dy;
    if(xa > xb){
        x = xb;
        y = yb;
        xEnd = xa;
    }else{
        x = xa;
        y = ya;
        xEnd = xb;
    }
    setPixel(x, y);
    while(x < xEnd){
        x++;
        if(p < 0)
            p += twoDy;
        else{
            if(tFactor > 0) //for positive slope
                y++;
            else //for negative slope
                y--;
            p += twoDyDx;
        }
        setPixel(x, y);
    }
}

void drawBoundary(pt winMin, pt winMax){
    int x, y;
    x = winMin.x;
    for(y = winMin.y; y < winMax.y; y++){
        setPixel(x,y, blueColor);
    }
    y = winMin.y;
    for(x = winMin.x; x < winMax.x; x++){
        setPixel(x,y, blueColor);
    }
    x = winMax.x;
    for(y = winMin.y; y < winMax.y; y++){
        setPixel(x,y, blueColor);
    }
    y = winMax.y;
    for(x = winMin.x; x < winMax.x; x++){
        setPixel(x,y, blueColor);
    }

}

int clipTest(float p, float q, float *u1, float *u2){
    float r;
    int retVal = TRUE;

    if(p < 0.0){
        r = q / p;
        if(r > *u2)
            retVal = FALSE;
        else
            if (r > *u1)
                *u1 = r;
    }
    else
        if (p > 0.0){
            r = q / p;
            if (r < *u1)
                retVal = FALSE;
            else if (r < *u2)
                *u2 = r;
        }
        else
            if(q < 0.0)
                retVal = FALSE;

        return (retVal);
}

void clipLine(pt winMin, pt winMax, pt p1, pt p2){
    float u1 = 0.0, u2 = 1.0, dx = p2.x - p1.x, dy;
    if(clipTest(-dx, p1.x - winMin.x, &u1, &u2))
        if(clipTest(dx, winMax.x - p1.x, &u1, &u2)){
            dy = p2.y - p1.y;
            if(clipTest(-dy, p1.y - winMin.y, &u1, &u2))
                if(clipTest(dy, winMax.y - p1.y, &u1, &u2)){
                    if(u2 < 1.0){
                        p2.x = p1.x + u2 * dx;
                        p2.y = p1.y + u2 * dy;
                    }
                    if(u1 > 0.0){
                        p1.x += u1 * dx;
                        p1.y += u1 * dy;
                    }
                    LineBresenham(ROUND(p1.x), ROUND(p1.y), ROUND(p2.x), ROUND(p2.y));
                }
        }
}
/* Window Procedure WndProc */
LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam){

    switch(message){
        case WM_PAINT:
            SetWindowHandle(hwnd);
            drawBoundary(winMin, winMax);
            clipLine(winMin, winMax, p1, p2 );
            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("Line Clipping");
    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,"Liang-Barsky Algorithm - 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;
}

1 comment:

  1. I want a program for line clipping for lines for slopes positive and less than 1 using liang barsky algorithm...

    ReplyDelete