Updating object scale to appear consistent regardless of distance from camera

This topic has 5 replies, 3 voices, and was last updated 3 months, 3 weeks ago by masj.

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2024-01-08 at 7:56 pm #69540

masj
Participant

Hello!

Linear algebra is def not my strength as a creative-type first. Hoping a kind technician in the V3D community can help me with something I’m trying to build.

The goal is to update the size of a given Object3D(s) to remain visually consistent, regardless of its distance from the app’s camera. Think I’m getting the distance between the object(s) and the camera correctly – was able to get this far:

function setObjectConsistentScale(objs) {
var [_vec1, _vec2] = [new v3d.Vector3(), new v3d.Vector3()];
objs.forEach(obj => {
var objDist = obj.getWorldPosition(_vec1).distanceTo(app.camera.getWorldPosition(_vec2));
console.log(objDist);
// obj.scale = (?, ?, ?);
});
}

What to do next is…where I need help, especially when we start potentially factoring in camera zoom, FOV, etc. Any guidance on the matter would be HUGELY appreciated. Thanks!

2024-01-08 at 8:45 pm #69541

xeon
Customer

Any chance you can describe the use case?

Xeon
Route 66 Digital
Interactive Solutions - https://www.r66d.com
Tutorials - https://www.xeons3dlab.com

2024-01-08 at 9:18 pm #69542
kdv
Participant
```
  function setObjectScale(mesh, factor) {
    if (app.camera.isOrthographicCamera)
      factor = ((app.camera.top - app.camera.bottom) / app.camera.zoom) / factor;
    else
      factor = (mesh.position.distanceTo(app.camera.position) * Math.tan(Math.PI * app.camera.fov / 360) * 2) / factor;
    mesh.scale.set(1, 1, 1).multiplyScalar(factor);
  }
```
Puzzles and JS. Fast and expensive.

If you don’t see the meaning in something it primarily means that you just don’t see it but not the absence of meaning at all.
2024-01-08 at 11:00 pm #69544

masj
Participant

@kdv, you are brilliant! Thank you once again for sharing your insights. Really appreciate your help.

Can I ask a follow up question re: the ‘factor’ arg?
I think I found a way manually to set ‘factor’ on a per-object basis via its bounding box & Math.cbrt to keep it at the same scale as inside the 3D model file itself, but was wondering if you knew of a cleaner/simpler way to do this via maths inside the function call, when an object’s bounding box will have grown/shrunk with the object’s scale (hope that make sense).

@xeon, for sure! I was envisioning something almost like fancy 3D UI annotation-like objects on the surface of model(s) in an app with lots of leeway for zooming, kind of like the feel of zooming in to a 2D map in an app, but w/ some proper 3D fanciness.

2024-01-08 at 11:10 pm #69545
kdv
Participant
masj wrote:

Can I ask a follow up question re: the ‘factor’ arg?

using this argument you can adjust the desired visual scale. Higher values make objects smaller. You may start with 5 and then adjust scales as needed.

The way to apply scaling per object:
```
    object.onBeforeRender = function() {
      setObjectScale(this, 5);
    };
```
Puzzles and JS. Fast and expensive.

If you don’t see the meaning in something it primarily means that you just don’t see it but not the absence of meaning at all.
2024-01-09 at 12:46 am #69546

masj
Participant

Thanks for the breakdown.
Again, you’ve been amazing, and thanks for the help!
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