Calculate Bounding Box of Hierarchy of Objects

Help & Support
1

If I have a parent with several child renderers, I want to be able to create a single bounding box model around all of them. Any clues how to do this?

Using a model - type box is fine but how do I calculate the size of it and it’s center position?

Thanks

2

Hi @Grimmy,

You will need to loop through all of the entities and their mesh instances and add/sum the bounding boxes.

That will give you the total bounding box that encloses all models. You can take a look at the model viewer → orbit-camera.js script, it includes a similar method used to frame your scene.

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3

This is great thanks but I’m creating a new box renderer and trying to scale it to the same size and scale as the bounding box but both the size and scale dont match. I have the following code where
boundingBoxEntitySize is a new pc.BoundingBox();

this.boundingBoxVisEntity.setLocalScale(this.boundingBoxEntitySize.halfExtents.scale(2));
this.boundingBoxVisEntity.setLocalPosition(this.boundingBoxEntitySize.center);
this.entity.addChild(this.boundingBoxVisEntity);

I’ve tried adding the boundingBoxVisEntity both before and after scaling/positioning and also tried setPosition but nothing comes close.

Failing that, how would I just go about rendering the bounding box so that I can actually see it?

4

This may be of help: Could somebody please kindly explain how to use DrawWireAlignedBox? - #2 by Leonidas

5

Thanks, but that code just seems to call some other internal function (this.app.drawWireAlignedBox(this.min, this.max, this.color):wink: and even once I have the result of that I would need to turn the result into an entity at correct position and scale…so effectively I would be doing exactly the same again but instead trying to match the size and position of the wireframe box instead of the boundingBoxEntitySize.

Maybe I should have said that I need the visualization as an entity so I can manipulate the material and do other stuff later.

6

I thought you were trying to visualize the bounding box, but know I understand you really want to scale an actual box entity to fit the bounding box.

Not sure what you are doing wrong though, try sharing an example project if possible.

7

Yes, I want an entity that matches exactly the bounding box. :slight_smile: The above code is really all there is…apart from my bounding box calculation:


 // Calculate the bounding box visualization
    this.boundingBoxEntitySize = this.calculateBoundingBox();

BoundingBoxVisualizer.prototype.calculateBoundingBox = function () {

   var meshInstances = this.entity.render.meshInstances;
    if (meshInstances.length > 0) 
    {
        var bbox = new pc.BoundingBox();
        bbox.copy(meshInstances[0].aabb);

        for (var i = 1; i < meshInstances.length; i++) 
        {
                bbox.add(meshInstances[i].aabb);
        }
    }

    return bbox;
};
8

See this post to see how to create an entity that is the same as the bounding box:

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