iOS使用4个角落的渐变创建UIImage

Question

我知道如何创建渐变UIImage，颜色从上到下变化。如下图所示：

[self linearGradientImageFromColors:@[(__bridge id)[UIColor blueColor].CGColor, (__bridge id)[UIColor purpleColor].CGColor, (__bridge id)[UIColor redColor].CGColor, (__bridge id)[UIColor yellowColor].CGColor]]



- (UIImage *)linearGradientImageFromColors:(NSArray*)colorArray
{
    CGSize textSize = self.bounds.size;
    CGFloat width = textSize.width;
    CGFloat height = textSize.height;

    CGSize size = CGSizeMake(width, height);
    CAGradientLayer *layer = [CAGradientLayer layer];
    layer.frame = CGRectMake(0, 0, size.width, size.height);
    layer.colors = colorArray;

    UIGraphicsBeginImageContextWithOptions(size,NO,0);
    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return  image;
}

但是我现在正试图找出如何实现以下类型：每个角落的颜色不同：

修改

我有点能够通过绘制4个单独的图像来实现更接近我想要的东西，其中每个图像是一个角落中的渐变颜色，而另一个角落是clearColor，然后组合所有4个图像以获得结果。然而，这给了我一个与我想要的不同（更暗）的结果。我哪里错了？

4角渐变尝试代码：

[self corneredGradientImageFromColors:@[[UIColor blueColor], [UIColor purpleColor], [UIColor yellowColor], [UIColor redColor]]]



- (UIImage *)corneredGradientImageFromColors:(NSArray*)colorArray
{
    CGSize textSize = self.bounds.size;
    CGFloat width = textSize.width;
    CGFloat height = textSize.height;
    CGSize size = CGSizeMake(width, height);

    //CGContextRef context = UIGraphicsGetCurrentContext();

    CAGradientLayer *layer1 = [CAGradientLayer layer];
    layer1.frame = CGRectMake(0, 0, size.width, size.height);
    layer1.colors = @[(__bridge id)((UIColor*)[colorArray objectAtIndex:0]).CGColor, (__bridge id)[UIColor clearColor].CGColor];
    layer1.startPoint = CGPointMake(0.0, 0.0);
    layer1.endPoint = CGPointMake(1.0, 1.0);

    UIGraphicsBeginImageContextWithOptions(size,NO,0);
    [layer1 renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *imagelayer1 = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CAGradientLayer *layer2 = [CAGradientLayer layer];
    layer2.frame = CGRectMake(0, 0, size.width, size.height);
    layer2.colors = @[(__bridge id)[UIColor clearColor].CGColor, (__bridge id)((UIColor*)[colorArray objectAtIndex:1]).CGColor];
    layer2.startPoint = CGPointMake(0.0, 1.0);
    layer2.endPoint = CGPointMake(1.0, 0.0);

    UIGraphicsBeginImageContextWithOptions(size,NO,0);
    [layer2 renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *imagelayer2 = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CAGradientLayer *layer3 = [CAGradientLayer layer];
    layer3.frame = CGRectMake(0, 0, size.width, size.height);
    layer3.colors = @[(__bridge id)((UIColor*)[colorArray objectAtIndex:2]).CGColor, (__bridge id)[UIColor clearColor].CGColor];
    layer3.startPoint = CGPointMake(0.0, 1.0);
    layer3.endPoint = CGPointMake(1.0, 0.0);

    UIGraphicsBeginImageContextWithOptions(size,NO,0);
    [layer3 renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *imagelayer3 = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CAGradientLayer *layer4 = [CAGradientLayer layer];
    layer4.frame = CGRectMake(0, 0, size.width, size.height);
    layer4.colors = @[(__bridge id)[UIColor clearColor].CGColor, (__bridge id)((UIColor*)[colorArray objectAtIndex:3]).CGColor];
    layer4.startPoint = CGPointMake(0.0, 0.0);
    layer4.endPoint = CGPointMake(1.0, 1.0);

    UIGraphicsBeginImageContextWithOptions(size,NO,0);
    [layer4 renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *imagelayer4 = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();



    UIGraphicsBeginImageContext(size);

    [imagelayer1 drawAtPoint:CGPointZero];
    [imagelayer2 drawAtPoint:CGPointZero];
    [imagelayer3 drawAtPoint:CGPointZero];
    [imagelayer4 drawAtPoint:CGPointZero];

    UIImage* result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return  result;
}

这实现了这个目标：

修改

这不是所提及的副本。我正在尝试创建一个UIImage，并且提到的副本既不会创建UIImage，也不会解决该问题。