5

将 Gif 转换为动画 UIImage 时，每帧的延迟都是从属性中提取的，kCGImagePropertyGIFDelayTime或者kCGImagePropertyGIFUnclampedDelayTime

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 在两种示例情况下都选择了正确的一种：

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其中一个示例图像的动画太慢或太快

有没有办法确定使用哪个属性？

谢谢

4

1 回答 1

7

最终使用了 webkit 方法，它选择了 unlamped、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;
}
于 2013-07-24T03:11:20.720 回答