# Crash when reading vertex data from a Geometry that has been updated in-place with less vertex data **URL:** \ **Category:** Bugs\ **Created:** [February 24, 2025, 7:20pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775 "2025-02-24T19:20:41Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![rapid.tore.levenstam](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/rapid.tore.levenstam/32/43255_2.png) [@rapid.tore.levenstam](https://forum.babylonjs.com/u/rapid.tore.levenstam)\ **Post date:** [February 24, 2025, 7:20pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775/1 "2025-02-24T19:20:41Z")
Repro: [Babylon.js Playground](https://www.babylonjs-playground.com/#KZ1C5A) There seems to be an issue reading vertex data from a `Geometry` if it has been updated at any point with fewer vertices than any previous vertex data. When querying for vertex data there is a constructor call to `Float32Array` which tries to fetch a view into the underlying data buffer with the same length of the original vertex data’s size. However, our newly updated vertex data has a smaller size than our original, causing an error to be thrown from the Float32Array constructor. The (bad) size that we’re trying to read is provided by the function caller to `VertexBuffer.getFloatData`, in this case it is `Geometry._totalVertices`. The `_totalVertices` field is automatically set when calling `Geometry.setVerticesBuffer` with the `VertexData.PositionKind`, which is in turn called by `Geometry.setVerticesData`. However, this value is never updated when Vertex Data is updated through `Geometry.updateVerticesData`. I guess one solution to this would be to update the field in the `Geometry.updateVerticesData` function. You could also argue that what the `Geometry` class is asking of the `VertexBuffer` is valid, as its actual GPU buffer still has the capacity of the original vertex data size (or the largest in the lifetime of the `VertexBuffer` if you update multiple times). But it doesn’t work like this currently either, as the CPU-side buffer of the data is set to the user-given array when updating the `VertexBuffer` which is smaller in this repro-case. Unsure which way to fix is best! Unfortunately I don’t have the time to set aside for a PR at the moment as I don’t have Babylon running locally currently, so any assistance would be greatly appreciated! Thanks, -Tore ---
**Author:** ![Deltakosh](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/deltakosh/32/26635_2.png) [@Deltakosh](https://forum.babylonjs.com/u/Deltakosh)\ **Post date:** [February 24, 2025, 8:20pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775/2 "2025-02-24T20:20:30Z")
Checking! ---
**Author:** ![Deltakosh](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/deltakosh/32/26635_2.png) [@Deltakosh](https://forum.babylonjs.com/u/Deltakosh)\ **Post date:** [February 24, 2025, 8:23pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775/3 "2025-02-24T20:23:55Z")
Ok this is expected. You cannot update a vertex buffer with less data. The vertex size is locked and readonly. So this is expected. Rendering still work as the indices keep the GPU data read in check but everything else will fail ---
**Author:** ![Deltakosh](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/deltakosh/32/26635_2.png) [@Deltakosh](https://forum.babylonjs.com/u/Deltakosh)\ **Post date:** [February 24, 2025, 8:26pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775/4 "2025-02-24T20:26:25Z")
> [@rapid.tore.levenstam](#): > > However, this value is never updated when Vertex Data is updated through `Geometry.updateVerticesData`. To extend on that, we assume the vertex buffer stays at the same size. I’m not super sure if I want to change such a fundamental case so close to our 8.0 release. I’ll give it a shot and if it ends up being controllable, I’d apply the fix and keep you posted ---
**Author:** ![Deltakosh](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/deltakosh/32/26635_2.png) [@Deltakosh](https://forum.babylonjs.com/u/Deltakosh)\ **Post date:** [February 24, 2025, 8:33pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775/5 "2025-02-24T20:33:04Z")
ok it SEEMS to be fine I’ll keep an eye on the PR to see how the tests react [Fix Geometry update with smaller buffer by deltakosh · Pull Request #16212 · BabylonJS/Babylon.js](https://github.com/BabylonJS/Babylon.js/pull/16212) ---
**Author:** ![rapid.tore.levenstam](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/rapid.tore.levenstam/32/43255_2.png) [@rapid.tore.levenstam](https://forum.babylonjs.com/u/rapid.tore.levenstam)\ **Post date:** [February 24, 2025, 8:50pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775/6 "2025-02-24T20:50:19Z")
> [@Deltakosh](#): > > Fix Geometry update with smaller buffer by deltakosh · Pull Request #16212 · BabylonJS/Babylon.js If this is a bit of a risky change, perhaps it could also be fixed by allowing the user to set the \_totalVertices field? That is possible today through the setVerticesData function in Geometry, but there is no such parameter for the updateVerticesData. ninja edit: Locally in our project I was able to get it working by simply setting the \_totalVertices field through a ts-ignore. So for us a parameter, like in the setVerticesData function, or a separate function to set the value, is probably enough at least for our issue. ---
**Author:** ![Deltakosh](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/deltakosh/32/26635_2.png) [@Deltakosh](https://forum.babylonjs.com/u/Deltakosh)\ **Post date:** [February 24, 2025, 9:14pm UTC](https://forum.babylonjs.com/t/crash-when-reading-vertex-data-from-a-geometry-that-has-been-updated-in-place-with-less-vertex-data/56775/7 "2025-02-24T21:14:25Z")
I feel better right now. I feel this is the right fix 😃