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OBB isn't centered (includes proposed fix) #5506

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zakaton opened this issue Apr 3, 2024 · 6 comments
Open

OBB isn't centered (includes proposed fix) #5506

zakaton opened this issue Apr 3, 2024 · 6 comments

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@zakaton
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zakaton commented Apr 3, 2024 •
edited

Using obb-collider for entities with child entities creates a collider that isn't centered, causing an offset

<html>
  <head>
    <script src="https://aframe.io/releases/1.5.0/aframe.min.js"></script>
  </head>

  <body>
    <a-scene embedded obb-collider="showColliders: true" xr-mode-ui="enabled: false">
      <a-entity obb-collider position="0 1.5 -1" rotation="0 20 0">
        <a-box scale="0.1 0.1 0.1" position="0 0.1 0" color="blue"></a-box>
        <a-box scale="0.1 0.1 0.1" position="0.5 0 0" color="blue"></a-box>
      </a-entity>
    </a-scene>
  </body>
</html>

I looked into the obb-collider.js and was able to create a fix by modifying the tick function to include the boundingBox's center. I made a simple build and you can see it in action in the glitch url above

tick: (function () {
        var auxPosition = new THREE.Vector3();
        var auxScale = new THREE.Vector3();
        var auxQuaternion = new THREE.Quaternion();
        var auxMatrix = new THREE.Matrix4();
        var boundingBoxCenter = new THREE.Vector3(); // FOR POSITION FIX

        return function () {
            var obb = this.obb;
            var renderColliderMesh = this.renderColliderMesh;
            var trackedObject3D = this.checkTrackedObject() || this.el.object3D;

            if (!trackedObject3D) {
                return;
            }

            trackedObject3D.updateMatrix();
            trackedObject3D.updateMatrixWorld(true);
            trackedObject3D.matrixWorld.decompose(auxPosition, auxQuaternion, auxScale);
            
            // POSITION FIX
            this.boundingBox.getCenter(boundingBoxCenter);
            boundingBoxCenter.sub(trackedObject3D.position);
            boundingBoxCenter.applyQuaternion(trackedObject3D.quaternion);
            auxPosition.add(boundingBoxCenter);

            // Recalculate collider if scale has changed.
            if (
                Math.abs(auxScale.x - this.previousScale.x) > 0.0001 ||
                Math.abs(auxScale.y - this.previousScale.y) > 0.0001 ||
                Math.abs(auxScale.z - this.previousScale.z) > 0.0001
            ) {
                this.updateCollider();
            }

            this.previousScale.copy(auxScale);

            // reset scale, keep position and rotation
            auxScale.set(1, 1, 1);
            auxMatrix.compose(auxPosition, auxQuaternion, auxScale);

            // Update OBB visual representation.
            if (renderColliderMesh) {
                renderColliderMesh.matrixWorld.copy(auxMatrix);
            }

            // Reset OBB with AABB and apply entity matrix. applyMatrix4 changes OBB internal state.
            obb.copy(this.aabb);
            obb.applyMatrix4(auxMatrix);
        };
    })(),
@dmarcos
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dmarcos commented Apr 4, 2024

Can try master? there was some recent fixes

@zakaton
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zakaton commented Apr 4, 2024

updated glitch example to include the master - same issue

@dmarcos
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dmarcos commented Apr 4, 2024

Feel free to open a PR. Thanks!

@zakaton
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zakaton commented Apr 4, 2024 •
edited

made a fork and added the change, but then I realized that when the entity is itself a child of another entity, the issue persists (I updated the glitch example so now neither solution works)

not sure how to fix it 🤷, but personally I can just modify my personal use-case so the child primitives are each obb-colliders instead of the parent entity

@dmarcos
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dmarcos commented Apr 5, 2024

Yeah. In this case for example:

<a-entity obb-collider position="0 1.5 -1" rotation="0 20 0">
  <a-box position="0 3 0" color="blue"></a-box>
   <a-box position="0 5 0" color="blue"></a-box>
 </a-entity>

In the image below the bounding box is centered in the parent but should be in the middle point between the child boxes in the y-axis:

Screenshot 2024-04-04 at 6 04 16 PM

General solution is the center of mass?

@dmarcos
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dmarcos commented Apr 5, 2024 •
edited

Definitely obb-collider doesn't work at the moment with shifted children with respect to the parent

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@dmarcos @zakaton