Hi, I'm playing now with hand tracking. I want to get position of hand inside a system update function. I was not sure if transform I'm getting from hand attached AnchorEntity (with trackingMode: .predicted) would give same results as handAnchors(at:) from hand tracking provider, so I started to read them both and compare. For handAnchors i tried using context.scene.timebase.sourceTimebase!.sourceClock!.time.seconds and CACurrentMediaTime() as timestamp source. They seem to use exactly same clock, so that doesn't matter, but:
for some reason update handler is always called twice with same context.deltaTime, but first time the query finds 0 entities, second time it finds them all. The query is the standard EntityQuery(where: .has(MyComponent.self)) and in update (matching: Self.query, updatingSystemWhen: .rendering). Here's part of logs:
System update called, entity count: 0, dt: 0.01000458374619484, absTime: 4654.222593541
System update called, entity count: 11, dt: 0.01000458374619484, absTime: 4654.22262525
System update called, entity count: 0, dt: 0.009999999776482582, absTime: 4654.249390875
System update called, entity count: 11, dt: 0.009999999776482582, absTime: 4654.249425
accounting for the double update calling I started to calculate time delta of absolute time between calls and they're most of the time much bigger, or much smaller than advertised by system's context.deltaTime, only sometimes they kind of match, for example:
system: (dt: 0.01000458374619484)
scene : (dt: 0.021419291667371) (absTime: 4654.222628125001)
and the very next call
system: (dt: 0.010009 166784584522)
scene : (dt: 0.0013097083328830195) (absTime: 4654.223937833334)
but sometimes
system: (dt: 0.009999999776482582)
scene : (dt: 0.009 112249999816413) (absTime: 4654.351299 166668)
Shouldn't those be more or less equal, or am I missing something?
In the end it seems that getting hand position from AnchorEntity and with handAnchors(at:) gives kind of same results, but at different time points, so I'd love to understand what's the correct way to use them and why time flows differently :).
--Edit--
P.S. Had to put spaces everywhere in logs between "9" and "1", otherwise post was blocked due to "sensitive content" :D
