int shape::intersect(Vec2d* _otherShapePoints, long _otherNumPoints, int _thisCurrentPoint){  // gets passed the third point to start 

     // new line just being drawn this happens once

     Vec2d P0a( this->pointList[_thisCurrentPoint-1].x,  this->pointList[_thisCurrentPoint-1].y ); //gets point minus one position

     Vec2d P0b( this->pointList[_thisCurrentPoint].x,  this->pointList[_thisCurrentPoint].y ); // gets  point 

     float M0 = ( P0b.y - P0a.y ) / ( P0b.x - P0a.x );  //slope of test line the one just being drawn

     float X, Y; //equation variables

     // check from first line through third last line of every existing line in shape

Vec2d P1a, P1b; // new point

     for( int i=0;i<_otherNumPoints-2;i++ ) {  // checks from first point to current point

          P1a =  _otherShapePoints[i]; // for each makes line segment from point P1a to P1b

          P1b =  _otherShapePoints[i+1];

         // check if the intersection is within line segment boundaries of the two segments

         float left0 = helpers::min( P0a.x, P0b.x );  // takes first line segment sees which is left boundry

         float right0 = helpers::max( P0a.x, P0b.x ); // right

         float left1 = helpers::min( P1a.x, P1b.x ); // takes current segment to be checked from for loop starting with first seg of pointarray

         float right1 = helpers:: max( P1a.x, P1b.x );// right

         float M1 = ( P1b.y - P1a.y ) / ( P1b.x - P1a.x ); //slope of old line segments

         if ( M0 != M1 ) {// if slopes are different they must cross somewhere

             X = ( P1a.y - P0a.y - P1a.x * M1 + P0a.x * M0 ) / ( M0 - M1 );  //y=mx+b for both they must cross somewhere so y=mx+b = y1=m1x1+b solve for x

             Y = P0a.y + ( X - P0a.x) * M0; // plug in x

             // if it does intersect    

             if ( X > left0 && X < right0 && X > left1 && X < right1 ) {  // if the intercept point is in between the two segments we are looking at it is crossing     

                 //numPoints = 0;  // for debugging

for (int h=0; h< numIntersects; h++){// look at all intercept points

  if ((intersects[h].x +1 >= X && X>= intersects[h].x -1) && (intersects[h].y +1 >= Y && Y >= intersects[h].y -1)){ // if already found don't add it give a buffer for no double trouble

  return -1;

  }

}

//else add put into array

int k = numIntersects;// be sure to give the realloc size

  k = k + 1;

        intersects = (Vec2d*) realloc( intersects, sizeof(Vec2d)*k );// variable array gets memory space according to size of

                 intersectPoint = Vec2d ( X,Y );  // store the intersection

intersects[numIntersects] = intersectPoint;

        numIntersects++; //increment intersects

//debug

printf( "%f %f point\n",X,Y); 

        printf( "%d num of inter\n",numIntersects); 

                return i; // return the intersected line

             }

         }

     }