Bug about camera matrix

Bugs
1

Hi everybody,

I noticed a bug since BABYLON Version 8.22.3.

Here’s what happens :

Version 8.22.1 :

2025-09-10_09h29_26

The zoom is working perfectly (item 15 of the camera matrix)

Actual version :

2025-09-10_09h30_24

Nothing is working.

Here’s the code in the slider function (num is the float returned by the slider):

updateScale(num) {
        // Récupère la matrice de projection de la caméra active
        var matrixia = scene.activeCamera.getProjectionMatrix();

        // Met à jour l'élément m[15] de la matrice avec le paramètre num
        matrixia._m[15] = num;

        // Applique les modifications à la matrice de projection de la caméra active
        scene.activeCamera.getProjectionMatrix().setRow(0, matrixia.getRow(0));
        scene.activeCamera.getProjectionMatrix().setRow(1, matrixia.getRow(1));
        scene.activeCamera.getProjectionMatrix().setRow(2, matrixia.getRow(2));
        scene.activeCamera.getProjectionMatrix().setRow(3, matrixia.getRow(3));

What happens in the last version :

Matrixia._m[15] = 0 when i’m looking at the console. So the zoom is not working any more. I tried to have a look with a PG but i did not manage to reproduce the bug.

If anyone could help me…

Thanks,

Boris

2

This is unfortunately impossible to tell without a repro as I do not remember any changes on our matrices recently.

3

cc @georgie our new Camera overlord

4

@sebavan,

I agree with you but it is sometimes very difficult to reproduce a bug in the playground when your app has several thousands of lines and many links and you do not know exactly where it is wrong.

But I can give you a link (privately of course) on our server and a way to reproduce the bug. I’ve done it recently and it worked.

So @georgie , if you have time to have a look on the problem, tell me and i will send you a link and a way to reproduce the bug.

Thanks very much.

5

Babylon.js Playground I verified the matrices and such without and success to repro :frowning:

6

yes @bvaisman if you can provide a way to reproduce i can investigate, thank you!

7

@bvaisman (r.e private repro link) I now see what you were saying – if you try updating m[15]=X and u check projectionMatrix again, the update is not persisted.

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this behavior change in your app is because of this change
FrameGraph: Fix TAA (broken by #17064) (#17091) · BabylonJS/Babylon.js@dfa0906
which calls camera.getProjectionMatrix(true), forcing recalc of projectionMatrix so your manual update is not taken into account (your code below)

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rather than your code updating the matrix value directly, why not move the camera position along the Z axis? you can set activeCamera.position.z directly to simulate zooming? Or you can scale the object itself?

I would recommend against modifying matrix values in your code - curious your thoughts / if others have different opinions!

cc @Evgeni_Popov

8

Thanks very much for your help.

But unfortunatly, I am not using only the zoom. I change all the parameters of the camera in the same way with other functions to align the 3D object to the 2D picture.

If I have to change something in my code, i’m ready to do it but I absolutely need to update the matrix.

For instance, is it possible to force the update with the markAsUpdated() function or another one ?

9

Sorry for this change, it was a bug fix for some use cases.

You should be able to fix it on your side by doing yourRTT._objectRenderer.dontSetTransformationMatrix = true;. If this works, I will add a getter for RTT._objectRenderer so that you don’t have to access private properties.

10

Sorry but i don’t find how to do it.

I’ve written this code before the camera matrix update functions but it does not work. May be my code is wrong because i’m not used to this functions.

this.rtt = new BABYLON.RenderTargetTexture("rtt", 1024, scene);
scene.activeCamera.customRenderTargets.push(this.rtt)
this.rtt._objectRenderer.dontSetTransformationMatrix = true
11

That should do it. Can you send me the link privately so I can look into it? Thank you!