proximity-activation.md

sample-sync-websockets: Proximity Activation

In the Synchronize Websockets doc we go over how to track some Decentraland events called positionChanged and rotationChanged.

Now we can tie it all together tracking the user's position, or the positions of all the characters connected to the server, and do something based on that.

---

Wait, school actually taught us something useful?

In the Decentraland Discord chat I was talking with a new pal, we were discussing some ideas about the API.

me: dood, I used Pythagoras' Theorem from school!
him: 😯 finally you got to use it!
me: 12+ years wasn't a total waste!
him: 😬

./scene/scene.tsx

import { Vector3Component } from "decentraland-api";

/**
 * Pythagoras' Theorem implementation
 *
 * Get the distance between two points.
 *
 * Note: It uses {x,z} not {x,y}. In Decentraland the y-coordinate refers to height.
 */
function distance(pos1: Vector3Component, pos2: Vector3Component): number {
  const a = pos1.x - pos2.x;
  const b = pos1.z - pos2.z;
  return Math.sqrt(a * a + b * b);
}

(If I got it wrong just post an issue. I wasn't really paying attention in school.)

What can we do with this? The Proximity Activation Technique is what.

A Vector3Component is just an object that stores {x, y, z} coordinates.

const player1 = { x: 1, y: 0, z: 1 }
const player2 = { x: 4, y: 0, z: 4 }
const activationDistance = 2
const spaceBetween = distance(player1, player2)

console.log("spaceBetween", spaceBetween)

if (spaceBetween <= activationDistance) {
  console.log("activate!")
} else {
  console.log("don't activate")
}

// CONSOLE OUTPUT:
// spaceBetween 4.242640687119285
// don't activate

If our users move a bit closer together, we can see the console output changes accordingly. If:

• player1 = { x: 3, y: 0, z: 3 }
• player2 = { x: 3.5, y: 0, z: 3.5 }

...then we get the following output:

// spaceBetween 0.7071067811865476
// activate!

Okay, we've got a system for proximity activation. This is what the sample-sync-websockets uses in order to light up the tiles and open the door.

As another player enters the scene, the server will sync their location and you will see tiles and/or the door activate in response.

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What can you imagine doing using this technique? Let me know!

Come find me in the Decentraland chat and show me what you come up with.

Thanks! -Tony Crowe @tcrowe

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