在GCD块中绘制到图像时的卡顿

时间:2012-12-23 00:25:49

标签: iphone ios cocoa-touch core-animation grand-central-dispatch

我有以下方法,它需要一些CAShapeLayers并将它们转换为UIImageUIImage在单元格中用于UITableView(非常类似于从您的某个库中选择照片时的照片应用)。从GCD块中调用此方法:

-(UIImage*) imageAtIndex:(NSUInteger)index
{
    Graphic *graphic = [[Graphic graphicWithType:index]retain];

    CALayer *layer = [[CALayer alloc] init];
    layer.bounds = CGRectMake(0,0, graphic.size.width, graphic.size.height);
    layer.shouldRasterize = YES;
    layer.anchorPoint = CGPointZero;
    layer.position = CGPointMake(0, 0);

    for (int i = 0; i < [graphic.shapeLayers count]; i++)
    {
        [layer addSublayer:[graphic.shapeLayers objectAtIndex:i]];
    }

    CGFloat largestDimension = MAX(graphic.size.width, graphic.size.height);
    CGFloat maxDimension = self.thumbnailDimension;
    CGFloat multiplicationFactor = maxDimension / largestDimension;
    CGSize graphicThumbnailSize = CGSizeMake(multiplicationFactor * graphic.size.width, multiplicationFactor * graphic.size.height);

    layer.sublayerTransform = CATransform3DScale(layer.sublayerTransform, graphicThumbnailSize.width / graphic.size.width, graphicThumbnailSize.height / graphic.size.height, 1);
    layer.bounds = CGRectMake(0,0, graphicThumbnailSize.width, graphicThumbnailSize.height);

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

    [layer release];
    [graphic release];

    return [image autorelease];
}

无论出于何种原因,当我滚动UITableView并加载图片时,它会有点卡顿。我知道GCD代码很好,因为它以前工作过,所以看起来这段代码中的某些东西导致了口吃。有谁知道那可能是什么? CAAnimation不是线程安全的吗?或者有没有人知道采取一堆CAShapeLayers并将其转换为UIImage的更好方法?

1 个答案:

答案 0 :(得分:1)

最后我相信:

[layer renderInContext:UIGraphicsGetCurrentContext()];

无法在单独的线程上完成,因此我必须执行以下操作:

UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
//draw the mutable paths of the CAShapeLayers to the context
UIImage *image = [UIGraphicsGetImageFromCurrentImageContext() retain];
UIGraphicsEndImageContext(); 

WWDC2012视频“在iOS上构建并发用户界面”中有一个很好的例子(我学会了这样做)