The TouchEvents spec says nothing about the order of touches in a TouchList. But when computing the 'rotation' angle it appears that hammer always computes the angle between touches[0] and touches[1]. If the touches happen to be in different positions in the array from event to event, this will result in 180 degree flipping back and forth. We saw an example of this in Chrome and although we're planning in fixing that case, it's possible there are others (eg. depending on the OS behavior, and possibly behavior in other browsers). I raised this as an issue in the TouchEvents spec but it sounds like we're unlikely to have the spec require touch points to have a consistent order in the list.
The TouchEvents spec says nothing about the order of touches in a TouchList. But when computing the 'rotation' angle it appears that hammer always computes the angle between touches[0] and touches[1]. If the touches happen to be in different positions in the array from event to event, this will result in 180 degree flipping back and forth. We saw an example of this in Chrome and although we're planning in fixing that case, it's possible there are others (eg. depending on the OS behavior, and possibly behavior in other browsers). I raised this as an issue in the TouchEvents spec but it sounds like we're unlikely to have the spec require touch points to have a consistent order in the list.