How to draw a line in SpriteKit efficiently

In my SpriteKit scene, user should be able to draw line with his/her finger. I have a working solution, if the line is long, FPS gets down to 4-6 and the line starts to get polygonal, as the image below:

To draw myline (SKShapeNode*), I collect points of touches movement in an NSMutableArray* noteLinePoints in this way

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGPoint touchPoint = [[touches anyObject] locationInNode:self.scene];
    SKNode *node = [self nodeAtPoint:touchPoint];

    if(noteWritingActive)
    {
        [noteLinePoints removeAllObjects];
        touchPoint = [[touches anyObject] locationInNode:_background];
        [noteLinePoints addObject:[NSValue valueWithCGPoint:touchPoint]];
        myline = (SKShapeNode*)node;
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    if(myline)
    {
        CGPoint touchPoint = [[touches anyObject] locationInNode:_background];
        [noteLinePoints addObject:[NSValue valueWithCGPoint:touchPoint]];
        [self drawCurrentNoteLine];
    }
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    if(myline)
    {
        myline.name = @"note";
        myline = nil;
    }
    NSLog(@"touch ended");
}

and I draw the line in this way

- (CGPathRef)createPathOfCurrentNoteLine
{
    CGMutablePathRef ref = CGPathCreateMutable();

    for(int i = 0; i < [noteLinePoints count]; ++i)
    {
        CGPoint p = [noteLinePoints[i] CGPointValue];
        if(i == 0)
        {
            CGPathMoveToPoint(ref, NULL, p.x, p.y);
        }
        else
        {
            CGPathAddLineToPoint(ref, NULL, p.x, p.y);
        }
    }

    return ref;
}

- (void)drawCurrentNoteLine
{
    if(myline)
    {
        SKNode* oldLine = [self childNodeWithName:@"line"];
        if(oldLine)
            [self removeChildrenInArray:[NSArray arrayWithObject:oldLine]];

        myline = nil;

        myline = [SKShapeNode node];
        myline.name = @"line";
        [myline setStrokeColor:[SKColor grayColor]];

        CGPathRef path = [self createPathOfCurrentNoteLine];
        myline.path = path;
        CGPathRelease(path);

        [_background addChild:myline];
    }
}

How can I fix this problem? because all subsequent lines are all polygonal only, I think because the fps is very low and sampling rate of touches automatically get also very low...

Please note that for the test I used an iPad 3 (my app needs to be working from iPad 2 model with iOS7)

Do not constantly create new SKShapeNodes, there is a bug which is causing your slowdown. Instead, only use 1 SKShapeNode (Or create a bunch but reuse them), and append the path with new info (So there is no need to constantly add the myline to the background)

Alternative:

Use 1 community SKSkapeNode for rendering of the path, then convert the SKShapeNode to a texture with view.textureFromNode, then add an SKSpriteNode with this new texture instead of the shape node