Regular appearance

(All demonstration GIFs are at half speed for better visualisation)

This tiny mod adds the telescopic piston arm animation seen in Bedrock Edition to Java, as well as the option for a squishier alternative animation and particle emission.

It's also compatible with the G4mespeed mod for smoother piston animations over all.

This mod requires the Fabric API to run! Grab it here -> https://www.curseforge.com/minecraft/mc-mods/fabric-api

Included are a few add-on Resource Packs which offer:

Sticky Piston sides
Squishing Bellows
Scissors/Springs

(all of these support PBR)

sticky sides bellows scissors/springs

Quick guide for Resource Pack developers:

Model the piston arm around the vanilla piston_head models and put those in your pack as normal
Split those models such that everything you want to not squish and to move at regular speed is in the piston_head_short models, and the arm parts are in a piston_arm model in the assets/telepistons/models/block/ directory

Add the following to your piston_arm.json:

"telepistons": {
	"squish":"false",
	"particles":"4",
	"squishedScale": [ 1, 1, 0 ]
    }

"squish" and "particles" determine whether the arm model gets squished and whether pistons emit steam particles respectively
"squishedScale" determines the scale of the arm model once fully squished, i.e. the piston has fully retracted. Z points forward, so a vector of [1, 1, 0] will squish the arm just in that direction, while a vector of [2,2,0] will also make it get twice as wide and tall as it is squished.

TelePistons

Fabric API