YYkit原代码（代码位置 - 类YYAsyncLayer.m 方法_displayAsync）：

UIGraphicsBeginImageContextWithOptions(self.bounds.size, self.opaque, self.contentsScale);
CGContextRef context = UIGraphicsGetCurrentContext();
if (self.opaque) {
    CGSize size = self.bounds.size;
    size.width *= self.contentsScale;
    size.height *= self.contentsScale;
    CGContextSaveGState(context); {
        if (!self.backgroundColor || CGColorGetAlpha(self.backgroundColor) < 1) {
            CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
            CGContextAddRect(context, CGRectMake(0, 0, size.width, size.height));
            CGContextFillPath(context);
        }
        if (self.backgroundColor) {
            CGContextSetFillColorWithColor(context, self.backgroundColor);
            CGContextAddRect(context, CGRectMake(0, 0, size.width, size.height));
            CGContextFillPath(context);
        }
    } CGContextRestoreGState(context);
}
task.display(context, self.bounds.size, ^{return NO;});
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

替换代码：

UIGraphicsImageRendererFormat *format = [[UIGraphicsImageRendererFormat alloc] init];
format.opaque = self.opaque;
format.scale = self.contentsScale;

UIGraphicsImageRenderer *renderer = [[UIGraphicsImageRenderer alloc] initWithSize:self.bounds.size format:format];
UIImage *image = [renderer imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
    CGContextRef context = rendererContext.CGContext;
    if (self.opaque) {
        CGSize size = self.bounds.size;
        size.width *= self.contentsScale;
        size.height *= self.contentsScale;
        CGContextSaveGState(context); {
            if (!self.backgroundColor || CGColorGetAlpha(self.backgroundColor) < 1) {
                CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
                CGContextAddRect(context, CGRectMake(0, 0, size.width, size.height));
                CGContextFillPath(context);
            }
            if (self.backgroundColor) {
                CGContextSetFillColorWithColor(context, self.backgroundColor);
                CGContextAddRect(context, CGRectMake(0, 0, size.width, size.height));
                CGContextFillPath(context);
            }
        } CGContextRestoreGState(context);
    }
    task.display(context, self.bounds.size, ^{return NO;});
}];