ios绘图系列五:绘制渐变CGContextDrawLinearGradient, CGContextDrawRadialGradient, CAGradientLayer

CGContextRef ctx = UIGraphicsGetCurrentContext();

//创建一个RGB的颜色空间
CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
//定义渐变颜色数组
CGFloat colors[] =
{
204.0 / 255.0, 224.0 / 255.0, 244.0 / 255.0, 1.00,
29.0 / 255.0, 156.0 / 255.0, 215.0 / 255.0, 1.00,
0.0 / 255.0,  50.0 / 255.0, 126.0 / 255.0, 1.00,
};

//创建一个渐变的色值 1:颜色空间 2:渐变的色数组 3:位置数组,如果为NULL,则为平均渐变,否则颜色和位置一一对应 4:位置的个数
CGGradientRef _gradient = CGGradientCreateWithColorComponents(rgb, colors, NULL, sizeof(colors)/(sizeof(colors[0])*4));
CGColorSpaceRelease(rgb);

//获得一个CGRect
CGRect clip = CGRectInset(CGContextGetClipBoundingBox(ctx), 20.0, 20.0);
//剪切到合适的大小
CGContextClipToRect(ctx, clip);
//定义起始点和终止点
CGPoint start = CGPointMake(20, 20);
CGPoint end = CGPointMake(20, 100);
//绘制渐变, 颜色的0对应start点,颜色的1对应end点,第四个参数是定义渐变是否超越起始点和终止点
CGContextDrawLinearGradient(ctx, _gradient, start, end, kCGGradientDrawsBeforeStartLocation);

//辐射渐变
start = CGPointMake(100, 80);//起始点
end = CGPointMake(100, 140); //终结点
//辐射渐变 start:起始点 20:起始点的半径 end:终止点 40: 终止点的半径 这个辐射渐变
CGContextDrawRadialGradient(ctx, _gradient, start, 20, end, 40, 0);

CAGradientLayer *gradient = [CAGradientLayer layer];//创建渐变层
gradient.frame = CGRectMake(20, 20, 100, 100);
[self.view.layer addSublayer:gradient];
//渐变层的颜色梯度数组
gradient.colors = @[(__bridge id)[UIColor colorWithRed:204.0 / 255.0 green:224.0 / 255.0 blue:244.0 / 255.0 alpha:1].CGColor,
(__bridge id)[UIColor colorWithRed:29.0 / 255.0 green:156.0 / 255.0 blue:215.0 / 255.0 alpha:1].CGColor,
(__bridge id)[UIColor colorWithRed:0.0 / 255.0 green:50.0 / 255.0 blue:126.0 / 255.0 alpha:1].CGColor];
//渐变层的相对位置,起始点为0,终止点为1,中间点为 (point-startpoint)/(endpoint-startpoint)
gradient.locations = @[@0,@.5,@1];
//渐变方向
gradient.startPoint = CGPointMake(0, 0);
gradient.endPoint = CGPointMake(0, 1);