ios - Create perpendicular line to CGPathRef -

i using skshapenodes dynamically draw lines updating path property user touches screen. once line complete, append new fixed length perpendicular line end of path.

i have looked cgaffinetransform rotate new line based on end point of path, far haven't had luck. tips or insight appreciated.

some of current code reference looks like:

        - (void)touchesmoved:(nsset *)touches withevent:(uievent *)event     {         uitouch* touch = [touches anyobject];         cgpoint positioninscene = [touch locationinnode:self];          //add line new coordinates user moved         cgpathaddlinetopoint(pathtodraw, null, positioninscene.x, positioninscene.y);     }   -(void)touchesended:(nsset *)touches withevent:(uievent *)event { //create local copy of path cgpathref mypath_ = pathtodraw;  cgpoint mypoint = cgpathgetcurrentpoint(pathtodraw);  //create rectangle append end of line         cgrect newrect = cgrectmake(mypoint.x, mypoint.y, 25, 3); cgpathref newpath = cgpathcreatewithrect(newrect, null);  //add new line end of path cgpathaddpath(newpath, null, mypath_);  //set shape node path drawn path         linenode.path = mypath_; } 

to perpendicular, can take vector pointing in direction of last line segment, swap x , y, , invert 1 of them. this:

cgpoint v = { currentpoint.x - lastpoint.x, currentpoint.y - lastpoint.y }; cgpoint perp; if (v.x == 0) {     perp.x = -v.y;     perp.y = v.x; } else {     perp.x = v.y;     perp.y = -v.x; } 

now can draw line in direction of perp, starting @ current point, this:

cgpathmovetopoint (somepath, currentpoint); cgpathaddlinetopoint (somepath, null, currentpoint.x + perp.x * length, currentpoint.y + perp.y * length); 

where length length of line segment want draw.

and don't forget set lastpoint currentpoint it's correct next time around:

lastpoint = currentpoint;