Core Graphices 设置渐变

Core Graphices 设置渐变 

Quartz 提供了两种设置渐变的方式  CGShadingRef and CGGradientRef

尝试CGGradientRef 的使用

import <UIKit/UIKit.h>

@interface GradientDemoA : UIView

@property (nonatomic,copy,nonnull)NSArray *colorArray;
@property (nonatomic,copy,nonnull) NSArray *locations;
@property (nonatomic,assign)CGPoint startPoint;
@property (nonatomic,assign)CGPoint endPoint;

- (void)showViewWithColorArray:(NSArray * _Nullable)colorArray GradientLocations:(NSArray * _Nullable)loc startPoint:(CGPoint)startPoint endPoint:(CGPoint)endPoint;
@end

#import "GradientDemoA.h"

@implementation GradientDemoA

- (instancetype)initWithFrame:(CGRect)frame{
    
    if (self = [super initWithFrame:frame]) {
        self.backgroundColor = [UIColor whiteColor];
    }
    return self;
}


- (void)showViewWithColorArray:(NSArray *)colorArray GradientLocations:( NSArray *)loc startPoint:(CGPoint)startPoint endPoint:(CGPoint)endPoint{
    
    self.colorArray = colorArray;
    self.locations = loc;
    self.startPoint = startPoint;
    self.endPoint = endPoint;
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {

    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGColorSpaceRef colorSpace  = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient;
    size_t num_location = self.colorArray.count;
    
    CGFloat components[self.colorArray.count*4];
    
    for (int i=0; i<self.colorArray.count; i++) {
        CGFloat *colorComponents = (CGFloat *)CGColorGetComponents(((UIColor *)self.colorArray[i]).CGColor);
        components[0+i*4] = colorComponents[0];
        components[1+i*4] = colorComponents[1];
        components[2+i*4] = colorComponents[2];
        components[3+i*4] = colorComponents[3];
        
    }
    
    CGFloat gendientLocations[self.locations.count];
    
    for (int j= 0; j<self.locations.count; j++) {
        
        gendientLocations[j] = (CGFloat)([self.locations[j] doubleValue]);
    }

//    参数的意义
    /*
     
     颜色空间 
     components  cgfloat 数组  RGB的颜色值
     {
        red1，green1，blue1，alpha1，
        red2，green2，blue2，alpha2，
        ...
     }
     gendientLocations  颜色渐变的点
     
     
    CGFloat gendientLocation[2] = {0.0,.......,1.0};
     
     num_location  颜色渐变点的个数；
     */
    
    
    gradient =  CGGradientCreateWithColorComponents(colorSpace, components, gendientLocations, num_location);

    
    /*
       开始点与结束点的tan值决定了渐变的角度；
     **/
    
    
    
//    CGContextDrawLinearGradient(context, gradient, self.startPoint, self.endPoint, kCGGradientDrawsBeforeStartLocation);
    
    CGContextDrawRadialGradient(context, gradient, CGPointMake(250, 250), 30, CGPointMake(30, 30), 80, kCGGradientDrawsAfterEndLocation);
    
    CGGradientRelease(gradient);

}


@end

参数更具体的意义请查看：

http://blog.csdn.net/u012890117/article/details/17606755

https://developer.apple.com/library/content/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_shadings/dq_shadings.html#//apple_ref/doc/uid/TP30001066-CH207-TPXREF101

测试代码：
- (void)gradientColor{
    GradientDemoA *my = [[GradientDemoA alloc] initWithFrame:CGRectMake(20, 80, 300, 300)];
    
    [my showViewWithColorArray:@[[[UIColor redColor] colorWithAlphaComponent:1.0],[[UIColor redColor] colorWithAlphaComponent:0.0],[[UIColor redColor] colorWithAlphaComponent:0.8]] GradientLocations: @[@(0.1),@0.5,@(0.8)] startPoint:CGPointMake(200,200) endPoint:CGPointMake(400, 0)];
    
    [self.view addSubview:my];
}

 图1：

图2：