Pixi.js: DeltaTime on Ticker update is incorrect

[eiko]

settings.TARGET_FPMS is supposed to set a limit for how many MS elapse each frame. By default, it equals 0.06, which roughly translates to a cap of 16 MS per frame.

But on line 390 of Ticker.js TARGET_FPMS is a direct part of the deltaTime calculation:

this.deltaTime = elapsedMS * settings.TARGET_FPMS * this.speed;

This takes elapsedMS which is generally around 16 MS, and multiplies it by 0.06, setting deltaTime to an average value of 1 MS, causing Ticker to claim an update rate of around 1000 FPS.

TARGET_FPMS is already used to calculate this._maxElapsedMS, so I believe it's already doing it's job. We should be able to remove it from the deltaTime calculation:

this.deltaTime = elapsedMS * this.speed;

[ivanpopelyshev]

deltaTime===1 corresponds to 1 frame, its working as intended. TARGET_FPMS is how many frames are elapsed per milliseconds. Yes, its strange, we should name it deltaFrame

That way if user writes element.x += 5 and it works fine on 60FPS, he cant just add * deltaTime to make smooth animations.

[eiko]

Ah, I see! The documentation's explanation of "a scalar time value" was a bit confusing. I still need deltaTime to be in fractional seconds, because my physics engine expects it that way. But I can just divide by TARGET_FPMS for that.

Thanks for your help! I'll leave this issue open in case people want to treat it as a documentation issue. Otherwise, feel free to close it!

[ivanpopelyshev]

You can write your own ticker with same interface and use it in your custom application class, and even assign PIXI.tickers.shared to it. or ticker.shared, i dont remember.

Make sure that AnimatedSprite and other things that you add in it, like your own tween manager, understand what exactly do you pass in.

[themoonrat]

Should at least fix this in v5, both documentation and variable name

[fightingcat]

This is really confusing, I have wasted my time on this.

[jcyuan]

const ms = deltaTime / PIXI.settings.TARGET_FPMS;

[jcyuan]

emmm.... I think this can be closed.

[lock[bot]]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.