以图片为中心 画放射状的梯度的光线

// 以图片为中心 画放射状的梯度的光线
    // Drawing code
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    size_t gradLocationsNum = 2;
    CGFloat gradLocations[2] = {0.0f, 1.0f};
    CGFloat gradColors[8] = {0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.75f};
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, gradColors, gradLocations, gradLocationsNum);
    CGColorSpaceRelease(colorSpace);
    
    //Gradient center
    CGPoint gradCenter= CGPointMake(self.bounds.size.width/2, self.bounds.size.height/2);
    //Gradient radius
    float gradRadius = MIN(self.bounds.size.width , self.bounds.size.height) ;
    //Gradient draw
    CGContextDrawRadialGradient (context, gradient, gradCenter,
                                 0, gradCenter, gradRadius,
                                 kCGGradientDrawsAfterEndLocation);
    CGGradientRelease(gradient);