ios - SpriteKit Generate Random Curl Line -

i working on project , need accomplish generate random curl line. @ point have have line randomly generated not curl. spawning points @ different x positions on every 0.5 seconds , connect points bezier. works except not curl. on picture below shown on 1) how have , on 2) how suppose make it. ideas how can ? using spritekit - objective c

basically need make , randomize a bézier (parametric) curve control points.

after read great answer , familiar terms, can try example (i assume scene , view size set correctly):

gamescene.m

#import "gamescene.h"  @implementation gamescene  -(void)didmovetoview:(skview *)view {  }  -(nsinteger)randomnumberbetween:(nsinteger)from to:(nsinteger)to {      return (int)from + arc4random() % (to-from+1); }   - (cgmutablepathref)generatepath {     cgmutablepathref path = cgpathcreatemutable();      cgpoint p0 =  cgpointmake(cgrectgetmidx(self.frame),self.scene.size.height-20.0f); //starting point little below upper edge of screen      cgpathmovetopoint(path, nil, p0.x, p0.y);      cgpoint p1 =     cgpointmake([self randomnumberbetween:150 to:300], self.scene.size.height- [self randomnumberbetween:150 to:300]);       cgpoint p2 = cgpointmake([self randomnumberbetween:150 to:300],[self randomnumberbetween:150 to:300]);      cgpoint p3 = cgpointmake(cgrectgetmidx(self.frame),0 + 20.0f); //ending point, little above bottom edge of screen      cgfloat v = 0.3;      cgfloat cp1x = p1.x+v * (p1.x-p0.x);     cgfloat cp1y = p1.y+v *  (p1.y-p0.y);     cgfloat cp2x = p2.x-v *  (p3.x-p2.x);     cgfloat cp2y = p2.y-v *  (p3.y-p2.y);         cgpathaddcurvetopoint(path,nil,cp1x,cp1y,cp2x,cp2y,p3.x,p3.y);        /*debug - not needed*/       skspritenode *sp0 = [skspritenode spritenodewithcolor:[skcolor yellowcolor] size:cgsizemake(5.0f,5.0f)];     sp0.zposition = 5;     sp0.position = p0;     sklabelnode *lp0 = [sklabelnode labelnodewithfontnamed:@"arialmt"];     lp0.fontcolor = [skcolor whitecolor];     lp0.fontsize = 20.0f;     lp0.text = @"p0";     lp0.position = cgpointmake(0.0f,-20.0f);     [sp0 addchild:lp0];     [self addchild:sp0];       skspritenode *sp1 = [skspritenode spritenodewithcolor:[skcolor yellowcolor] size:cgsizemake(5.0f,5.0f)];     sp1.zposition = 5;     sp1.position = p1;     sklabelnode *lp1 = [sklabelnode labelnodewithfontnamed:@"arialmt"];     lp1.fontcolor = [skcolor whitecolor];     lp1.fontsize = 20.0f;     lp1.position = cgpointmake(0.0f,15.0f);     lp1.text = @"p1";     [sp1 addchild:lp1];     [self addchild:sp1];      skspritenode *sp2 = [skspritenode spritenodewithcolor:[skcolor yellowcolor] size:cgsizemake(5.0f,5.0f)];     sp2.zposition = 5;     sp2.position = p2;     sklabelnode *lp2 = [sklabelnode labelnodewithfontnamed:@"arialmt"];     lp2.fontcolor = [skcolor whitecolor];     lp2.fontsize = 20.0f;     lp2.position = cgpointmake(0.0f,15.0f);     lp2.text = @"p2";     [sp2 addchild:lp2];     [self addchild:sp2];       skspritenode *sp3 = [skspritenode spritenodewithcolor:[skcolor yellowcolor] size:cgsizemake(5.0f,5.0f)];     sp3.zposition = 5;     sp3.position = p3;     sklabelnode *lp3 = [sklabelnode labelnodewithfontnamed:@"arialmt"];     lp3.fontcolor = [skcolor whitecolor];     lp3.fontsize = 20.0f;     lp3.position = cgpointmake(0.0f,15.0f);     lp3.text = @"p3";     [sp3 addchild:lp3];     [self addchild:sp3];        skshapenode *p0p1 = [skshapenode node];     p0p1.zposition = 2;     cgmutablepathref path1 = cgpathcreatemutable();     cgpathmovetopoint(path1, null, p0.x, p0.y);     cgpathaddlinetopoint(path1, null, p1.x, p1.y);     p0p1.path = path1;     [p0p1 setstrokecolor:[uicolor greencolor]];     [self addchild:p0p1];      skshapenode *p2p3 = [skshapenode node];     p2p3.zposition = 2;     cgmutablepathref path2 = cgpathcreatemutable();     cgpathmovetopoint(path2, null, p2.x, p2.y);     cgpathaddlinetopoint(path2, null, p3.x, p3.y);     p2p3.path = path2;     [p2p3 setstrokecolor:[uicolor greencolor]];     [self addchild:p2p3];      return path; }  -(void)touchesbegan:(nsset *)touches withevent:(uievent *)event {      [self removeallchildren];      skshapenode *yourline = [skshapenode node];     yourline.zposition = 1;      yourline.path = [self generatepath];      [yourline setlinewidth:5];      [yourline setstrokecolor:[skcolor redcolor]];      [self addchild:yourline];  } 

most of code used visual debugging , not needed in order randomize curve. important part first part of method generatepath. here result: