How to access previous frame using Orion?

[wenjiewu0427]

Hi guys,
I am new to Orion, and currently putting my old projects together using the V3 API. I used to access previous frames from leap controller by Controller.frame(Id) . However, so far I can't find a way to access previous frames from leap provider. I can only access the current frame by LeapProvider.CurrentFrame. Does anyone know how to do this? Your answers will be greatly appreciated!!!

[Death111]

I do not know this. But I guess you could hold a reference to the last frame

Frame lastFrame;

void Update(){
     Frame currentFrame = provider.CurrentFrame;
     if(lastFrame==null)lastFrame = currentFrame; // init lastFrame
     
     // logic

     lastFrame = currentFrame;
}

[Joe_Ward]

You can do as Death111 suggests, and that is probably easiest if you only need the previous frame or so.

Otherwise, the Controller still maintains a history queue of previous frames. However, these frames haven't been transformed into the Unity coordinate system, so you would also need to do that (at some performance and memory cost):

controller = LeapServiceProvider.GetLeapController();
Frame oldLeapFrame = controller.Frame(23); // 23 frames back in the history
if(oldFrame != null){
    LeapTransform conversionTransform = transform.GetLeapMatrix();
    Frame oldTransformedCopy = oldFrame.TransformedCopy(conversionTransform);
}

This uses the transform of the current GameObject as the new basis of the Leap coordinates in the frame (and is essentially what the LeapServiceProvider does).

Note that Controller.Frame(id) was never correct. The Frame() function takes a History parameter, not an Id. The history parameter just counts back in time by that number of frames and has a maximum value of 60.

Note that I'm considering removing the history buffer from the Controller altogether and making it the responsibility of the client code to maintain a history buffer -- if desired. Most apps probably don't need one.

[AndrewHodrien]

Hi Joe (or anyone else who can please answer),

I am attempting to introduce a delay using Orion by displaying the Leap Hands movement from a certain number of frames in the past (equivalent to a specific amount of time - should be under 1 second).

I got this to work in pre-Orion assets following your suggestion of the history buffer here -

If it is a very short delay less than .5 seconds, then the easiest way is probably to alter the HandController script to get past frames rather than the current frame. The Controller object maintains a frame history buffer of 60 frames. Controller.Frame() gets the most recent frame; Controller.Frame(10) gets the tenth newest frame, and so on. At 120fps, this would give you a delay of up to .5 seconds. Obviously it would be frame rate dependent, but you could adjust the timing by looking at the F…

However, I can't currently achieve this with Orion as the script appears to be different. Can you please confirm:

1) is there a history buffer with Orion or has it been removed (as your suggestion above)?

2) if still available, please confirm which script this is contained in and where so I know which part I need to alter with a specific frame number (as I am unable to find something equivalent to the history buffer code for pre-Orion assets mentioned in link I posted).

3) is the code you mentioned above responding to Death111 the version of the history buffer for Orion or simply how to transform frames into the Unity coordinate system. Depending on your answer - is this code I need to add in somewhere?

4) Could you please clarify the performance and memory cost you mentioned - would this influence the latency and/or accuracy of Leap Motion tracking?

5) if the history buffer is no longer available please can you advise on what code I need to add for Orion to maintain my own history buffer (to create the delay I need).

Apologies for all the questions as have limited knowlege of scripting. This is urgent for developing a demo for a research study so if you (or anyone else) can advise on above ASAP I would really appreciate it

Many thanks, Andrew