iOS CALayer-实现颜色的渐变和曲线图

最近研究了一下颜色的渐变

效果，下面简单抽出一个类的代码，方便查看：

#import 

@interface YXLayerView : UIView
{
    CAShapeLayer * _lineLayer,* _maskLayer;
    CAGradientLayer * _backgroundLayer;
}

@end

#import "YXLayerView.h"

@implementation YXLayerView

- (instancetype)init
{
    self = [super init];
    if (self) {
        [self inits];
    }
    return self;
}

- (instancetype)initWithCoder:(NSCoder *)coder
{
    self = [super initWithCoder:coder];
    if (self) {
        [self inits];
    }
    return self;
}

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self inits];
    }
    return self;
}

- (void)inits
{
    self.backgroundColor = [UIColor grayColor];
    self.clipsToBounds = YES;
    
    _maskLayer = [[CAShapeLayer alloc] init];
    
    _backgroundLayer = [[CAGradientLayer alloc] init];
    _backgroundLayer.colors = @[(id)[UIColor redColor].CGColor,(id)[UIColor greenColor].CGColor,(id)[UIColor blueColor].CGColor];
    _backgroundLayer.startPoint = CGPointMake(0.5, 0);
    _backgroundLayer.endPoint = CGPointMake(0.5, 1.0);
    [self.layer addSublayer:_backgroundLayer];
    
    _lineLayer = [[CAShapeLayer alloc] init];
    _lineLayer.lineCap = kCALineCapRound;
    _lineLayer.lineJoin = kCALineJoinRound;
    _lineLayer.fillColor = [UIColor clearColor].CGColor;
    _lineLayer.strokeColor = [UIColor redColor].CGColor;
    _lineLayer.lineWidth = 5.0;
    [self.layer addSublayer:_lineLayer];
}

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
    CGRect bounds = self.bounds;
    CGFloat space = CGRectGetWidth(bounds)/4.0;
    CGFloat y = CGRectGetHeight(bounds)/2.0;
    UIBezierPath * bezierPath = [UIBezierPath bezierPath];
    [bezierPath moveToPoint:CGPointMake(0, y)];
    [bezierPath addQuadCurveToPoint:CGPointMake(space, y - 10) controlPoint:CGPointMake(space/2.0, y - 80)];
    [bezierPath addQuadCurveToPoint:CGPointMake(2 * space, y - 10) controlPoint:CGPointMake(space + space/2.0, y - 80)];
    [bezierPath addQuadCurveToPoint:CGPointMake(3 * space, y - 40) controlPoint:CGPointMake(2 * space + space/2.0, (y - 40)/2.0)];
    [bezierPath addQuadCurveToPoint:CGPointMake(4 * space, y) controlPoint:CGPointMake(3 * space + space/2.0, y/2.0)];
    _lineLayer.path = bezierPath.CGPath;
    
    _backgroundLayer.frame = bounds;
    [bezierPath addLineToPoint:CGPointMake(CGRectGetWidth(bounds), CGRectGetHeight(bounds))];
    [bezierPath addLineToPoint:CGPointMake(0, CGRectGetHeight(bounds))];
    [bezierPath closePath];
    _maskLayer.path = bezierPath.CGPath;
    _backgroundLayer.mask = _maskLayer;
}

@end