Wrong result of PickingInfo.getNormal with thin instances

kzhsw · March 25, 2025, 6:52am

OS: any
Engine: any
Version: 5.57.1 ~ 7.54.1
Playground:

Steps to reproduce:

Click the plane
Look at the lines

Expected:
Normals should be perpendicular to the plane

Actual:

Code:

github.com/BabylonJS/Babylon.js

packages/dev/core/src/Collisions/pickingInfo.ts

019a8c593


      
                  ? Vector3.FromArrayToRef(positions, indices[this.faceId * 3 + 2] * 3, tmp2)

                  : tmp2.copyFromFloats(positions[(this.faceId * 3 + 2) * 3], positions[(this.faceId * 3 + 2) * 3 + 1], positions[(this.faceId * 3 + 2) * 3 + 2]);

          

              const p1p2 = vertex1.subtract(vertex2);

              const p3p2 = vertex3.subtract(vertex2);

          

              result = Vector3.Cross(p1p2, p3p2);

          }

          

          const transformNormalToWorld = (pickedMesh: AbstractMesh, n: Vector3) => {

              let wm = pickedMesh.getWorldMatrix();

          

              if (pickedMesh.nonUniformScaling) {

                  TmpVectors.Matrix[0].copyFrom(wm);

                  wm = TmpVectors.Matrix[0];

                  wm.setTranslationFromFloats(0, 0, 0);

                  wm.invert();

                  wm.transposeToRef(TmpVectors.Matrix[1]);

          

                  wm = TmpVectors.Matrix[1];

              }

Evgeni_Popov · March 25, 2025, 8:53am

Thanks for reporting, this PR will fix the problem:

Note that you have to enable thin instance picking for this to work (ground.thinInstanceEnablePicking = true).

kzhsw · March 25, 2025, 9:03am

Seems ci failed.

Evgeni_Popov · March 25, 2025, 9:10am

This should be fixed.

kzhsw · March 26, 2025, 12:56am

Should picking thin instance mesh be skipped if thinInstanceEnablePicking not enabled? Current code picks it like it does not have thin instances, false positives might be produced. (But this is breaking old code depending on this behavior)

Evgeni_Popov · March 26, 2025, 11:02am

It’s by design, thinInstanceEnablePicking indicates that the picking should go to the thin instance level when/if the mesh has thin instances, it’s not a global picking on/picking off switch. It comes in addition to the Mesh.isPickable switch.

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Wrong result of PickingInfo.getNormal with thin instances

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