HowTo : Scale + ThinInstances

Questions
1

Hello,

Up to this point, I hadn’t encountered any issues as I hadn’t been using thin instances. However, thin instances have now introduced a translation problem whenever I attempt to scale models. As someone relatively new to 3D development, despite scouring numerous forum posts, I’ve been unable to find a solution.

I use the assetsManager to load assets, and due to variations in the sizes of models, upon the successful completion of a task in the assetsManager, I apply a scale (as defined in a configuration file).

For instance, I apply a scale of 0.01 to task.loadedMeshes (which contains 3 meshes) simply by using: node.scaling = new Vector3(0.01, 0.01, 0.01); on each mesh (since the model is very large).

Upon rendering, I see my model scaled as expected. However, when I attempt to translate the model using a matrix, it barely moves; it’s as if it’s operating within its “local matrix” or something like that.

Initially, I had:

const matrix: Matrix = Matrix.Translation(x, y, z);
thinInstancesWorldMatrices.set(matrix.toArray(), id * 16);

I considered that perhaps I should multiply the matrix with a scaling matrix, but the outcome seemed even worse. I also tried to scale the root node (rootnodes[0]) of InstantiatedEntries from container.instantiateModelsToScene, the scaling is working but change nothing to the translation problem.

In reality, I’m facing a similar issue with rotation: I apply a rotation upon task load (also by configuration). However, when I endeavor to move the unit in a particular direction, at times, it moves in the opposite direction, seemingly influenced by the initial rotation.

Could you advise on how to correctly implement transformations on a loaded container/mesh, such as rotation or scaling please ?

This video illustrates the problem: https://youtu.be/uoFXEefp1Mo

I try to understand this post… :thinking:

Other question: if we have a “character mesh” with children meshes, we can use the same thinInstance matrix for each child right ?

Thank you

2

Check this playground

As soon as we scale to 2, translations are also scaled.
Without the initial rotation, units move in opposite directions.

Bonus question : is there a better way than looping on child meshes ?

4

I also found this post (2021) with this playground as solution.

The solution say to use this code :

const scale = new Vector3(2, 2, 2);
const rot = new Quaternion.RotationYawPitchRoll(Math.PI/3, 0, 0);
const trans = new Vector3(-1, 2, 0);
var newMat = Matrix.Compose(scale, rot, trans);
sphere.thinInstanceSetMatrixAt(idx, newMat);

From what I understand we can also do something like this to avoid Quaternion (which cancel my initial rotation on container load) :

const matrix: Matrix = scaleMatrix
      .multiply(rotationMatrix)
      .multiply(translationMatrix);

UPDATE : this is indeed the solution . But it is not working in the given playground because the buffer is static, see later comments.

Notes :

  • my glb model have a scale of 1, 1, 1. But when I load it, I must set scale it at (1, 1, 1) explicitly otherwise the positioning is totally wrong. Strange behavior which does not help to debug. Updated playground
5

Hi.

Just to be sure about scaling behavior, did you export your model from Blender by yourself or find the glb directly ?

I cannot test right now but maybe these will help: Babylon.js docs

Since you ignore root node in your loading it may explain strange behavior.

Bye

1 Like
6

I found the model on Sketchfab, so I don’t know. But there is the same problem with the player.glb from babylon, here is a cleaned playground. Try to comment the scale 1,1,1.

7

Sorry I add infos in my original message

8

Indeed, importing objects is a nightmare for a beginner like me:

  • what we see in Blender is not always what we really have depending mysterious Blender config
  • we don’t really know what we export, depend on options (Z → Y, left/right handed)
  • Babylon also do changes automatically when importing (default conf of GLB loader when using assetManager)

So know I try to stop the headaches: my assets come with some initial transformations (scale & rotation) :sweat_smile:

9

Indeed, It explains why we (sometimes) have to (re)scale to 1 + rotate of 180 on Y, like my previous pg !

10

Most (all) of your orientation problems comes from the fact that Babylon uses a left handed coordinate system, while meshes are defined in a right handed system in a gltf/glb file. We have to set a special transformation (180° Y rotation and a -1 Z scale) on the root object to account for this difference. You will make your life much easier if you set the scene to be right handed by doing scene.useRightHandedSystem = true, because in that case the transformation is the identity.

Here’s how to fix your PG:

2 Likes
12

You right, at the beginning I also tried to switch to right handed, but my initial tests were incorrect.

Can someone please take a look at this playground, given as solution in another post ? The first sphere should scale, but it is not.

13

@Evgeni_Popov This is my last playground which works perfectly : https://playground.babylonjs.com/?#T8Y5DY#20

Now I just change the loaded .glb, look the result: https://playground.babylonjs.com/?#T8Y5DY#30

I understand that the model is probably exported with different parameters, but how the hell the result can be totally broken ? This is not a right handed problem, isn’t it ?

14

It does not scale because the default for staticBuffers has been changed to true for performance reasons. So, you have to pass false when calling thinInstanceSetBuffer:

No, it is a problem with the model itself. The meshes are children of a node with a 0.01 scale + a 90° rotation around X. The navmesh is not aware of it, so the matrices it returns can’t be used “as is”. I tried to fix it by multiplying the matrix with the inverse matrix of the parent node of the meshes:

Note that I reset the scale vector (line 4) to (1,1,1), and I also had to account for the 90° rotation around X line 138.

You’ll save yourself a lot of sweat if you ensure that all meshes are exported with an identity matrix from the DCC tool.

2 Likes
15

Thank you !! I see I still have a lot to learn :smile:

16

Hi @ylacaute, I’ve solved similar issues in the past by merging the imported model before doing anything with it. I’m not sure it’ll solve your issue, and (disclaimer) I did not go in depth on every aspect of the thread, but wanted to drop this here in case it helps. :v:

1 Like