# [LITE] Custom setParent Hierarchy and Pivot Inversion Quirks in WebGPU Backend

Feature requests
1

Hello all!

I am working on implementing a custom, performance-critical setParent framework layer inside the minimalist @babylonjs/lite ecosystem.
The core objective is allowing both standard primitive meshes and custom text geometry paragraphs to seamlessly inherit transformations from parent nodes (like a tracking mesh or an animated background panel) while allowing them to animate and rotate cleanly around their own custom local pivot centers

I have created two distinct implementation approaches and ran into a few interesting spatial mathematical anomalies that I need help resolving.

Approach A: Custom Row/Column Transposed setParent (v0.0.6b Beta)

  1. Playground Sandbox Live: Babylon Lite Playground

  2. Behavior Profile: This implementation transforms standard primitives (e.g., matching a box child to a sphere parent) exactly as designed!

  3. The Issue: The calculations break down when passing a custom pivot offset (centerXOffset / centerYOffset) for left-aligned typography blocks.
    The text mesh fails to resolve the correct values, causing an orbital spiral rotation anomaly instead of a local central spin.
    Mathematical Quirk Discovered: Inside this custom invertParentWorld iteration logic, the matrix layout transposes strangely.
    Translation components map directly to indices 3, 7, and 11 instead of the expected column-major terminal indices 12, 13, and 14.
    Interestingly, modifying the child’s relative Z-coordinate causes index 15 to dynamically shift (e.g., matching values like -15, -29, -49),
    yet standard meshes translate and rotate perfectly here.

Another example of setParent 6b Beta

The exact visible request of what i try to do is in this Playground.

  1. Playground Sandbox Live: Babylon Lite Playground

Approach B: Built-in mat4 Mathematical Suite (v0.0.7 Beta)

To align cleanly with native framework transformations, I built a secondary iteration path leveraging the built-in mat4Invert and mat4Decompose utilities

  1. Playground Sandbox Live: Babylon Lite Playground

  2. The Issue: I am unable to make the lifecycle updates bind correctly. Right after the “AFTER Decomposed simulation World” pass executes, the engine logs the decomposed local coordinate translation as _x: -15, yet the actual visible mesh rendering position remains locked directly in the canvas center!

Log Output:


--- DEBUG INITIAL setParent ID: test2 ---
parentMesh id: sphere2_parent position:  {"_x":15,"_y":2,"_z":0}
childMesh id: simulation-paragraph position:  {"_x":0,"_y":1,"_z":0}
childMesh expected to transform into this position:  {"x":0,"y":0,"z":0}
childMesh centerXOffset: 0 centerYOffset: 0
parentWorld [1,0,0,0,0,1,0,0,0,0,1,0,15,2,0,1]
invParentWorldDefault: {"0":1,"1":0,"2":0,"3":0,"4":0,"5":1,"6":0,"7":0,"8":0,"9":0,"10":1,"11":0,"12":-15,"13":-2,"14":0,"15":1}
is normal mesh POS: NORMAL X: 0 Y: 0 Z: 0
childWorldPivotMatrix: [1,0,0,0,0,1,0,0,0,0,1,0,0,0,0,1]
bakedLocalMatrix?: [1,0,0,0,0,1,0,0,0,0,1,0,-15,-2,0,1]
Decomposed TRS: {"translation":{"x":-15,"y":-2,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1},"scale":{"x":1,"y":1,"z":1}}
AFTER Decomposed simulation World: [1,0,0,0,0,1,0,0,0,0,1,0,0,0,0,1]
simulation possition:  {"_x":-15,"_y":-2,"_z":0}

It seems like the mesh’s reactive ObservableVec3 registers receive the values,
but the underlying matrix cache isn’t invalidating or updating correctly after decomposition.

4. Technical Constraints & Framework Visibility Notes

While digging into the architecture to resolve these translation mismatches, I noticed that a significant portion of the core mathematical optimization classes are not currently exposed in the package public exports list.

  1. mat4-transform.ts (e.g., transformCoordinatesToRef, transformNormalToRef) are not exposed
    github: Babylon-Lite/packages/babylon-lite/src/math/mat4-transform.ts at master · BabylonJS/Babylon-Lite · GitHub

  2. mat4-multiply-into.ts (mat4MultiplyInto) is completely unexposed:
    github: Babylon-Lite/packages/babylon-lite/src/math/mat4-multiply-into.ts at master · BabylonJS/Babylon-Lite · GitHub

Because these high-performance, unrolled, zero-allocation utilities are hidden, writing custom framework matrix workarounds forces code duplication.

What is the recommended approach in Babylon Lite to bake a permanent custom pivot matrix into a child mesh during setParent() initialization without breaking the reactive TRS observables or creating a rendering lag?

Any insights or assistance on these math loops would be highly appreciated!

Thank you!

3

Seems like i misunderstand some things!!

The way i try to do it, is almost impossible, as many Math mat4* functions is not exposed!

So i build a new one PG, and i use only functions that are available..

it does what i want!!

You can try to change the positions for normal meshes in line 123, and line 134,

for custom mesh in line 146, and line 245.

As you can see, cannot center the custom mesh.

what does need to center properly?
how can i set/change pivot to center in custom mesh??