PA1 - úkol 3.2 (Ořezávání úseček)

#ifndef __PROGTEST__
#include <stdio.h>
#endif /* __PROGTEST__ */
void swapNumbers ( double *a, double *b );
void rearangeRectangle ( double *rx1, double *ry1, double *rx2, double *ry2 );
int pointPosition ( double x, double y, double rx1, double ry1, double rx2, double ry2 );
int clipLine ( double rx1, double ry1, double rx2, double ry2, double * ax, double * ay, double * bx, double * by );
#ifndef __PROGTEST__
int main ( int argc, char * argv[] )
 {
    double ax, ay, bx, by, rx1, ry1, rx2, ry2;
    puts ( "ax, ay, bx, by, rx1, ry1, rx2, ry2" );
    scanf ( "%lf %lf %lf %lf %lf %lf %lf %lf", &ax, &ay, &bx, &by, &rx1, &ry1, &rx2, &ry2 );
    printf ( "\nclipline exitcode: %d\n", clipLine( rx1, ry1, rx2, ry2, &ax, &ay, &bx, &by ) );
    printf ( "ax: %f\nay: %f\nbx: %f\nby: %f\n", ax, ay, bx, by );

    return 0;
 }
#endif /* __PROGTEST__ */

void swapNumbers ( double *a, double *b )
 {
    *a += *b;
    *b = *a - *b;
    *a = *a - *b;
 }

void rearangeRectangle ( double *rx1, double *ry1, double *rx2, double *ry2 )
 {
    if ( *rx1 > *rx2 )
        swapNumbers ( rx1, rx2 );
    if ( *ry1 < *ry2 )
        swapNumbers ( ry1, ry2 );
 }

int pointPosition ( double x, double y, double rx1, double ry1, double rx2, double ry2 )
 {
    int position = 0; /* inside */
    if ( y > ry1 ) /* point is above rectangle */
        position += 1;
    if ( y < ry2 ) /* point is bellow rectangle */
        position += 2;
    if ( x > rx2 ) /* point is on the right side of the rectangle */
        position += 4;
    if ( x < rx1 ) /* point is on the left side of the rectangle */
        position += 8;
    return position;
 }

int clipLine ( double rx1, double ry1, double rx2, double ry2, double * ax, double * ay, double * bx, double * by )
 {
    int aPosition, bPosition;
    int *actualPosition;
    double *actualX, *actualY;
    rearangeRectangle ( &rx1, &ry1, &rx2, &ry2 );
    while ( 1 )
     {
        aPosition = pointPosition ( *ax, *ay, rx1, ry1, rx2, ry2 );
        bPosition = pointPosition ( *bx, *by, rx1, ry1, rx2, ry2 );
        if ( !( aPosition | bPosition ) ) /* whole line is already inside */
            return 1;
        if ( aPosition & bPosition ) /* whole line is outside */
            return 0;
        if ( !aPosition ) /* a is inside */
         {
            actualX = bx;
            actualY = by;
            actualPosition = &bPosition;
         }
        else
         {
            actualX = ax;
            actualY = ay;
            actualPosition = &aPosition;
         }
        if ( *actualPosition & 1 ) /* actual point is above rect */
         {
            *actualX = *ax + ( *bx - *ax ) * ( ry1 - *ay ) / ( *by - *ay );
            *actualY = ry1;
         }
        else if ( *actualPosition & 2 ) /* actual point is bellow rect */
         {
            *actualX = *ax + ( *bx - *ax ) * ( ry2 - *ay ) / ( *by - *ay );
            *actualY = ry2;
         }
        else if ( *actualPosition & 4 ) /* actual point is on the right side of the rectangle */
         {
            *actualY = *ay + ( *by - *ay ) * ( rx2 - *ax ) / ( *bx - *ax );
            *actualX = rx2;
         }
        else /* actual point is on the left side of the rectangle */
         {
            *actualY = *ay + ( *by - *ay ) * ( rx1 - *ax ) / ( *bx - *ax );
            *actualX = rx1;
         }
     }
 }