Colorful Hilbert Curves from Level 1 to Level 5

EYHilbertCurveView.h

// erkanyildiz
// 20170608-0308+0900
//
// EYHilbertCurveView.h

#import <UIKit/UIKit.h>


@interface EYHilbertCurveView : UIView

- (void)drawWithLevel:(NSInteger)level;
- (void)drawWithLevel:(NSInteger)level color:(UIColor *)color lineWidth:(CGFloat)lineWidth;
- (void)drawWithLevel:(NSInteger)level color:(UIColor *)color lineWidth:(CGFloat)lineWidth unitSize:(CGFloat)unitSize animationDuration:(CGFloat)animationDuration;

@end

EYHilbertCurveView.m

// erkanyildiz
// 20170608-0308+0900
//
// EYHilbertCurveView.m

#import "EYHilbertCurveView.h"


@interface EYHilbertCurveView ()
{
    CGFloat size;
    CGPoint current;
    UIBezierPath* path;
}
@end


@implementation EYHilbertCurveView

- (void)drawWithLevel:(NSInteger)level
{
    [self drawWithLevel:level color:nil lineWidth:1 unitSize:0.0 animationDuration:0.0];
}


- (void)drawWithLevel:(NSInteger)level color:(UIColor *)color lineWidth:(CGFloat)lineWidth
{
    [self drawWithLevel:level color:color lineWidth:lineWidth unitSize:0.0 animationDuration:0.0];
}


- (void)drawWithLevel:(NSInteger)level color:(UIColor *)color lineWidth:(CGFloat)lineWidth unitSize:(CGFloat)unitSize animationDuration:(CGFloat)animationDuration
{
    if (unitSize == 0)
    {
        CGFloat minSize = MIN(self.bounds.size.width, self.bounds.size.height);
        size = minSize / powf(2.0, level + 1);
        current = (CGPoint){0.5 * size, 0.5 * size};

        if(minSize == self.bounds.size.width)
            current.y += (self.bounds.size.height - minSize) * 0.5;
        else
            current.x += (self.bounds.size.width - minSize) * 0.5;
    }
    else
    {
        size = unitSize;
        current = CGPointZero;
    }

    path = UIBezierPath.bezierPath;
    [path moveToPoint:current];
    
    [self hilbert:level x:0 y:1];

    CAShapeLayer* layer = CAShapeLayer.layer;
    layer.path = path.CGPath;
    layer.fillColor = UIColor.clearColor.CGColor;
    layer.strokeColor = (color ? color : UIColor.blackColor).CGColor;
    layer.lineWidth = (lineWidth != 0.0) ? lineWidth : 1.0;
    layer.lineCap = kCALineCapSquare;
    
    [self.layer addSublayer:layer];
    
    if(animationDuration != 0.0)
    {
        CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
        anim.duration = animationDuration;
        anim.repeatCount = 1.0;
        anim.fillMode = kCAFillModeForwards;
        anim.removedOnCompletion = NO;
        anim.fromValue = @(0.0);
        anim.toValue = @(1.0);
        [layer addAnimation:anim forKey:@""];
    }
}


-(void)hilbert:(NSInteger)level x:(NSInteger)x y:(NSInteger)y
{
    if(level < 0)
        return;
    
    [self hilbert:level-1 x:y y:x];
    [self path:x y:y];
    
    [self hilbert:level-1 x:x y:y];
    [self path:y y:x];
    
    [self hilbert:level-1 x:x y:y];
    [self path:-x y:-y];

    [self hilbert:level-1 x:-y y:-x];
}


-(void)path:(NSInteger)x y:(NSInteger)y
{
    [path addLineToPoint:current];
    current.x += (x * size);
    current.y += (y * size);
    [path addLineToPoint:current];
}

@end

https://dribbble.com/shots/3551017-Hilbert-Curves-from-Level-1-to-Level-5