ios - GIFS 的 DelayTime 或 UnclampedDelayTime

Question

将 Gif 转换为动画 UIImage 时，每个帧的延迟是从属性 kCGImagePropertyGIFDelayTime 或 kCGImagePropertyGIFUnclampedDelayTime

中提取的

像这样:

NSString *frameKeyPath = [NSString stringWithFormat:@"%@.%@",(NSString*)kCGImagePropertyGIFDictionary,kCGImagePropertyGIFUnclampedDelayTime];
CFDictionaryRef cfFrameProperties = CGImageSourceCopyPropertiesAtIndex(source,i,nil);
NSDictionary *frameProperties = (__bridge NSDictionary*)cfFrameProperties;
NSNumber *delayTimeProp = [frameProperties valueForKeyPath:frameKeyPath];

Chrome 在两个例子中都选择了正确的:

kCGImagePropertyGIFDelayTime = 0.1:http://i.imgur.com/tX9cjUO.gif

kCGImagePropertyGIFUnclampedDelayTime = 0.01:http://i.minus.com/iIOyK7SKp8TYc.gif

为每种情况选择一个会导致示例图像之一的动画效果太慢或太快

有没有办法确定要使用的属性？

谢谢

Answer 1

最终使用 webkit 方法选择，unclamped，clamped 或 0.1 默认值

+ (float)frameDurationAtIndex:(NSUInteger)index source:(CGImageSourceRef)source
{
    float frameDuration = 0.1f;
    CFDictionaryRef cfFrameProperties = CGImageSourceCopyPropertiesAtIndex(source,index,nil);
    NSDictionary *frameProperties = (__bridge NSDictionary*)cfFrameProperties;
    NSDictionary *gifProperties = frameProperties[(NSString*)kCGImagePropertyGIFDictionary];

    NSNumber *delayTimeUnclampedProp = gifProperties[(NSString*)kCGImagePropertyGIFUnclampedDelayTime];
    if(delayTimeUnclampedProp) {
        frameDuration = [delayTimeUnclampedProp floatValue];
    } else {

        NSNumber *delayTimeProp = gifProperties[(NSString*)kCGImagePropertyGIFDelayTime];
        if(delayTimeProp) {
            frameDuration = [delayTimeProp floatValue];
        }
    }

    // Many annoying ads specify a 0 duration to make an image flash as quickly as possible.
    // We follow Firefox's behavior and use a duration of 100 ms for any frames that specify
    // a duration of <= 10 ms. See <rdar://problem/7689300> and <http://webkit.org/b/36082>
    // for more information.

    if (frameDuration < 0.011f)
        frameDuration = 0.100f;

    CFRelease(cfFrameProperties);
    return frameDuration;
}