`getHashCode`of Vector3 class does not work on some x y z values

The hash code of a Vector3 should be unique for a specific x,y,z values but it’s not in this example:

const vecA = new Vector3(
0.5982134154656932,
0.4042086778904232,
-0.056697209589591804
);

const vecB = new Vector3(
  0.6545249297519544,
  0.46514853581665117,
  -0.029312843053122293
);

const vecC = new Vector3(
  5,
  6,
  7 
);
console.log("Vector A:", vecA);
console.log("Vector A hash", vecA.getHashCode());

console.log("Vector B:", vecB);
console.log("Vector B hash", vecB.getHashCode());

console.log("Vector C:", vecC);
console.log("Vector C hash", vecC.getHashCode());

Screenshot 2022-01-06 at 15.41.59

The method seems to work well on VectorC, but it returns 0 for vector A and B, and they are different.

I guess that is a bug.
BabylonJs Version : 4.2

zephyrol

2 Likes

Hello and welcome :wink:

I’ll have a look today!

1 Like

Here is the PR: Hash code fix by deltakosh · Pull Request #11726 · BabylonJS/Babylon.js (github.com)

4 Likes

Thank you for your reactivity! Is it possible to release this fix within Babylon.js v4 ?

3 Likes

Nope, we only released 4.2.1 for the camera issue as it was a breaking change from the browsers. This was the first time we needed to do that and I hope the latest :slight_smile: Here the behavior is not changing from 4.2.

Why not upgrading to 5.0 beta ?

Because it’s a beta and we are in production.

I also have another question… why are those hash numbers? Why not dead simple strings that can be computed with string concatenation?

PS: We are using Babylon.js primitive hash as a way to handle cache for deeply immutable data structures.
In the future it would be great for Babylon.js to have immutable primitives structures, particularly given the raise of functional paradigm and where ECMAScript is going with Record/Tupple: GitHub - tc39/proposal-record-tuple: ECMAScript proposal for the Record and Tuple value types. | Stage 2: it will change!

We call it beta for a lack of a better name. It is far more stable than 4.2 :slight_smile:

Regarding hash we are moving to a simpler solution for high end structure with the UniqueID.

For low level structure like vector we favor the perf with simple, limited but fast system.
You can already get a string computation for each vector with toString(). The hash is here to let store the info in an int compliant storage

Furthermore, having deeply immutable vectors would be problematic for perf as every new operation will not be doable in place and will then generate GC. Which we are constantly fighting against

1 Like