CIFilter減慢滾動

Question

我正在將CIFilter應用到UIImage，但它正在減慢滾動我的UITableView。我能做什麼？

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 
    static NSString *simpleTableIdentifier = @"tweetCell"; 

    TweetCell *cell = (TweetCell *)[tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier]; 
    if (cell == nil) 
    { 
     NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"TweetCell" owner:self options:nil]; 
     cell = [nib objectAtIndex:0]; 
    } 

    cell.tweet.text = _tweets[indexPath.row][@"text"]; 

    NSDictionary *tweetData = _tweets[indexPath.row]; 
    NSString *profilePhotoURL = _profilePhotos[tweetData[@"username"]]; 

    UIImage *bgPicture = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:profilePhotoURL]]]; 

    dispatch_async(dispatch_get_main_queue(), ^(void){ 

    CIFilter *gaussianBlurFilter = [CIFilter filterWithName:@"CIGaussianBlur"]; 
    [gaussianBlurFilter setDefaults]; 
    [gaussianBlurFilter setValue:[CIImage imageWithCGImage:[bgPicture CGImage]] forKey:kCIInputImageKey]; 
    [gaussianBlurFilter setValue:@0.7 forKey:kCIInputRadiusKey]; 

    CIImage *outputImage = [gaussianBlurFilter outputImage]; 
    CIContext *context = [CIContext contextWithOptions:nil]; 
    CGRect rect   = [outputImage extent]; 

    rect.origin.x  += (rect.size.width - bgPicture.size.width)/2; 
    rect.origin.y  += (rect.size.height - bgPicture.size.height)/2; 
    rect.size   = bgPicture.size; 

    CGImageRef cgimg  = [context createCGImage:outputImage fromRect:rect]; 
    UIImage *image  = [UIImage imageWithCGImage:cgimg]; 
    CGImageRelease(cgimg); 

    cell.bgP.image = image; 

    }); 

    return cell; 
} 

我的意思是我已經添加了使得滾動更好一點的調度片。但是，當我在UITableView上滾動速度非常快時，圖像和圖像過濾器會被加載，但在滾動時會經常出現凹凸或鋸齒狀。

Answer 1

將dispatch_async用於其他線程，然後在完成時更新。

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 

    CIFilter *gaussianBlurFilter = [CIFilter filterWithName:@"CIGaussianBlur"]; 
    [gaussianBlurFilter setDefaults]; 
    [gaussianBlurFilter setValue:[CIImage imageWithCGImage:[bgPicture CGImage]] forKey:kCIInputImageKey]; 
    [gaussianBlurFilter setValue:@0.7 forKey:kCIInputRadiusKey]; 

    CIImage *outputImage = [gaussianBlurFilter outputImage]; 
    CIContext *context = [CIContext contextWithOptions:nil]; 
    CGRect rect   = [outputImage extent]; 

    rect.origin.x  += (rect.size.width - bgPicture.size.width)/2; 
    rect.origin.y  += (rect.size.height - bgPicture.size.height)/2; 
    rect.size   = bgPicture.size; 

    CGImageRef cgimg  = [context createCGImage:outputImage fromRect:rect]; 
    UIImage *image  = [UIImage imageWithCGImage:cgimg]; 
    CGImageRelease(cgimg); 
    dispatch_async(dispatch_get_main_queue(), ^{ 
     cell.bgP.image = image; 
    }); 
});