[solved] Rotate Mesh based on Camera Rotation in Alpha AND Beta

[ziguri]

Hi there,

i do react on a camera change using

camera.onViewMatrixChangedObservable

Then i watch camera.alpha and camera.beta values and calculate their difference (considering modulo 2*PI) to the previous invocation of camera.onViewMatrixChangedObservable. Lets call it cam_alpha_diff.

Using this alpha and beta values I am able to rotate a submesh (a BABYLON.Mesh.CreatePlane mesh located in the WorldMatrix origin) of my scene with mesh.rotate(AXIS, cam_alpha_diff)

This works fine as long as i just wanna rotate the submesh around one axis. For instance only around the BABYLON.Axis.Y with the negative cam_alpha_diff.

If i wanna rotate the submesh in both alpha and beta direction i can not use the BABYLON.Axis.Y and BABYLON.Axis.X as rotating axis anymore. (except for the first camera movement). I kind of need to re-calcutate the rotation axis after each change of the camera.

My approach:

• Initialize a vector3 as BABYLON.Axis.Y
• Rotate the vector3 with the negative cam_alpha_diff using BABYLON.Matrix.RotationAxis and BABYLON.Vector3.TransformCoordinates
• Use the resulting vector3 as new rotation axis
• Do the same with another vector3 for BABYLON.Axis.X

But if i do it for both alpha and beta is kind of "going round in circles". 

Whats the best way to apply both alpha and beta camera rotations to a submesh?

Any hints?

My final goal is that the submesh always faces the camera no matter how i rotate the camera (an ArcRotateCamera).

Thanks.

[Gijs]

Can't you just use billboard mode?

[ziguri]

@Gijs,

you are totally right. This completely solves my issue. I didn't know that the billboard mode exists at all.

Thank you. Appreciated.

Issue solved!

[Wingnut]

Hey ziguri... glad you found the solve.  "Billboard" is sort of a strange word for "mesh look-at cam", isn't it?  I think so.

Can I ask... Did you do a docs search for 'lookAt' or 'look at' or something else?

I'm just curious.  That search would have failed to find info about billboard.

I'm trying to figure a way to make billboardMode easier to find information-about.  Or maybe more precise, easier to find THAT TERM and what it is used-for.

I'm wondering if a new tutorial might be wise... "Aiming, Tracking, LookAts, and Billboarding"  (or similar).  All about making stuff aim-at or follow other stuff. 

- Teaches about the unwanted z-rotation problems of billboarding when nearing poles.

- Tells about targets and lockedTargets.

-  Getting and setting directions for ALL types of nodes.  Perhaps teach Up(), Forward(), and maybe POV stuff.

-  Teaches how to build a lockedLookAt()  (when camera is the target, mesh lockedLookAt == billboardMode, right?  hmm.)

-  Shows how to derive directions from one thing to another, and what can be done with those directions and magnitudes.

- Getting distances (maybe)

You know... cool aim-at junk...  for dummies... like Wingnut.    Thinkin' 

But yeah, ziguri (and anyone else), if you DID search our docs, can you tell us what words you tried?  'aim'?  'direction'?  'face'?  'lookAt'?  'towards'?  *shrug*.  (thx)

[ziguri]

Hey wingnut,

it's true i was not able to find the Billboard function. That's why i tried to implement it by myself.

A tutorial would be great - a small official Playground Example even better.

I was looking for:

- React on camera rotation / movement

- Mesh facing camera

- mesh rotation matrix

camera.onViewMatrixChangedObservable did help me. A hint from this observale to billboard would be great too.

 

Thanks for your work and effort!