Estimating the time of frame onset using window.requestAnimationFrame

Hi all,

I would like to double-check the duration of each frame, by approximating the timestamp when each frame occurs. I have two questions related to this.

I noticed that in the PsychoJS scheduler code, a timestamp for the next frame flip is recorded when requestAnimationFrame() is called. FrameDuration appears to be represented by the variable self._lastDelta; calculated by subtracting the current timestamp from the previous timestamp. Unfortunately, it seems like these timestamp variables are local variables, as I cannot access them directly in a code component.

Question 1) Is there anyway to access the timestamp variables set in Scheduler and store them in a datafile?

Relevant scheduler code:

			// store frame delta for `Window.getActualFrameRate()`
2.				const lastTimestamp = self._lastTimestamp === undefined ? timestamp : self._lastTimestamp;
4.				self._lastDelta = timestamp - lastTimestamp;
5.				self._lastTimestamp = timestamp;
7.				// render the scene in the window:
8.				self._psychoJS.window.render();
10.				// request a new frame:
11.				requestAnimationFrame(update);
12.			};
14.			// start the animation:
15.			requestAnimationFrame(update);
16.		}

My current solution is to run window.requestAnimationFrame in the each frame tab of a code component. This seems to work quite well in approximating the frame duration. However …

Question 2) Would running requestAnimationFrame in the each frame tab of a code component substantially increase the computational strain of running the experiments?

Sorry for the long post and many thanks in advance for any help provided!