CoreGraphics,创建半圆有阴影渐变色背景图片

一、创建椭圆path

绘制水平渐变渐变色

#import <UIKit/UIKit.h>
@interface UIImage (Tools)
+ (UIImage *)lineGradientImageWithSize:(CGSize)size colors:(NSArray *)colors;
@end

#import "UIImage+Tools.h"
@implementation UIImage (Tools)
+ (UIImage *)lineGradientImageWithSize:(CGSize)size colors:(NSArray *)colors
{
    //创建CGContextRef
    UIGraphicsBeginImageContext(size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    //创建CGMutablePathRef
    CGMutablePathRef path = [self pathWithSize:size radisu:size.height/2];
    // 画图
    [self drawLinearGradient:context path:path colors:colors];
    //注意释放CGMutablePathRef
    CGPathRelease(path);
    //从Context中获取图像，并显示在界面上
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

/**
 创建圆角的path

 @param size
 @param radius
 @return path
 */
+ (CGMutablePathRef)pathWithSize:(CGSize)size radisu:(CGFloat)radius
{
    //创建CGMutablePathRef
    CGMutablePathRef path = CGPathCreateMutable();
    
    //绘制Path
    CGFloat width = size.width;
    CGFloat height = size.height;
    CGPathMoveToPoint(path, NULL, radius, height);
    CGPathAddArc(path, NULL, radius, radius, radius, M_PI_2, -M_PI_2, 0);
    CGPathAddLineToPoint(path, NULL, width-radius, 0);
    CGPathAddArc(path, NULL, width-radius, radius, radius, -M_PI_2, M_PI_2, 0);
    CGPathAddLineToPoint(path, NULL, width-radius, height);
    CGPathCloseSubpath(path);
    return path;
}

/**
 绘制水平方向线性渐变图片

 @param context
 @param path
 @param colors
 */
+ (void)drawLinearGradient:(CGContextRef)context path:(CGPathRef)path colors:(NSArray *)colors
{
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGFloat locations[] = { 0.0, 1.0 };
    
    NSMutableArray *colorList = [NSMutableArray array];
    for(UIColor *color in colors){
        if ([color isKindOfClass:[UIColor class]]) {
            [colorList addObject:(__bridge id)color.CGColor];
        }else{
            [colorList addObject:color];
        }
    }
    
    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colorList, locations);
    
    
    CGRect pathRect = CGPathGetBoundingBox(path);
    
    //具体方向可根据需求修改
    CGPoint startPoint = CGPointMake(CGRectGetMinX(pathRect), CGRectGetMinY(pathRect));
    CGPoint endPoint = CGPointMake(CGRectGetMaxX(pathRect), CGRectGetMinY(pathRect));
    
    CGContextSaveGState(context);
    CGContextAddPath(context, path);
    CGContextClip(context);
    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);
    CGContextRestoreGState(context);
    
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);
}
@end

创建一个渐变背景，有阴影的按钮

#import <UIKit/UIKit.h>

@interface GradientBgButton : UIButton

@end

#import "GradientBgButton.h"
#import "UIImage+Tools.h"
@interface GradientBgButton()

@property (nonatomic,assign) CGSize oldSize;
@end
@implementation GradientBgButton

- (void)layoutSubviews
{
    [super layoutSubviews];
    if(!CGSizeEqualToSize(self.bounds.size, self.oldSize)){
        self.oldSize = self.bounds.size;
        NSArray *normalColors =  @[[UIColor redColor],[UIColor greenColor]];
        [self setBackgroundImage:[UIImage lineGradientImageWithSize:self.bounds.size colors:normalColors] forState:UIControlStateNormal];
        
        NSArray *hightColors = @[[UIColor yellowColor],[UIColor purpleColor]];
        [self setBackgroundImage:[UIImage lineGradientImageWithSize:self.bounds.size colors:hightColors] forState:UIControlStateHighlighted];
        
        self.layer.shadowColor = [UIColor blueColor].CGColor;
        self.layer.shadowOffset = CGSizeMake(0,-1);
        self.layer.shadowOpacity = 0.5;
        self.layer.shadowRadius = 5;
        
        // 单边阴影 顶边
        CGFloat height = self.bounds.size.height;
        CGFloat width = self.bounds.size.width;
        CGFloat radius = height/2;
        CGRect shadowRect = CGRectMake(radius, height, width-radius*2, self.layer.shadowRadius);
        UIBezierPath *path = [UIBezierPath bezierPathWithRect:shadowRect];
        self.layer.shadowPath = path.CGPath;
    }
}
@end