Comment implémenter un zoom avant par pincement un zoom arrière en js

Does anyone know of a really good Javascript pinch-zooming algorithm? This is trickier than I had imagined, as you have to scale -AND- translate to keep the pinch zooming centered between your fingers.

And I want it to do pure translation when the user moves two fingers - kept an equal distance apart from each other - around the screen, i.e., this moving two fingers in unison should act like a single- finger "pan". 

Ce que j’ai essayé :

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