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Fix incorrect computation of bounding boxes #841

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Merged
merged 2 commits into from
May 11, 2022
Merged

Fix incorrect computation of bounding boxes #841

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3a72b47
Fix bounding box computation.
kring May 9, 2022
3b73e88
Update CHANGES.md.
kring May 9, 2022
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6 changes: 6 additions & 0 deletions CHANGES.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,11 @@
# Change Log

### ? - ?

##### Fixes :wrench:

- Fixed a bug introduced in v1.13.0 that could lead to incorrect axis-aligned bounding boxes.

### v1.13.1 - 2022-05-05

##### Breaking Changes :mega:
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17 changes: 8 additions & 9 deletions Source/CesiumRuntime/Private/CesiumGltfPrimitiveComponent.cpp
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Expand Up @@ -183,14 +183,10 @@ struct CalcBoundsOperation {
glm::max(glm::length(halfAxes[0]), glm::length(halfAxes[1]));
sphereRadius = glm::max(sphereRadius, glm::length(halfAxes[2]));

FVector xs(halfAxes[0].x, halfAxes[1].x, halfAxes[2].x);
FVector ys(halfAxes[0].y, halfAxes[1].y, halfAxes[2].y);
FVector zs(halfAxes[0].z, halfAxes[1].z, halfAxes[2].z);

FBoxSphereBounds result;
result.Origin = VecMath::createVector(center);
result.SphereRadius = sphereRadius;
result.BoxExtent = FVector(xs.GetAbsMax(), ys.GetAbsMax(), zs.GetAbsMax());
result.BoxExtent = FVector(sphereRadius, sphereRadius, sphereRadius);
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There's still a comment that says the sphere only has to reach the side of the box, is that still applicable / correct?

Also is all the stuff with the half-axes necessary in the BoundingSphere conversion, can't we just convert the sphere radius from meters to centimeters? Could we assume getTilesetToUnrealWorld is a rigid transform + a meters to centimeters scaling?

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I was trying to avoid making any assumptions about the transformation, since it's just a parameter to the method. So instead I construct a bounding box around the sphere, transform the box, and then build a sphere inset in the box. The comment is referring to the fact that the sphere only needs to be inset in the box, rather than fully contain it. There could very well be a better way to do this, but I think it works reasonably well.

return result;
}

Expand All @@ -207,14 +203,17 @@ struct CalcBoundsOperation {
double sphereRadius = glm::max(glm::length(corner1), glm::length(corner2));
sphereRadius = glm::max(sphereRadius, glm::length(corner3));

FVector xs(halfAxes[0].x, halfAxes[1].x, halfAxes[2].x);
FVector ys(halfAxes[0].y, halfAxes[1].y, halfAxes[2].y);
FVector zs(halfAxes[0].z, halfAxes[1].z, halfAxes[2].z);
double maxX = glm::abs(halfAxes[0].x) + glm::abs(halfAxes[1].x) +
glm::abs(halfAxes[2].x);
double maxY = glm::abs(halfAxes[0].y) + glm::abs(halfAxes[1].y) +
glm::abs(halfAxes[2].y);
double maxZ = glm::abs(halfAxes[0].z) + glm::abs(halfAxes[1].z) +
glm::abs(halfAxes[2].z);

FBoxSphereBounds result;
result.Origin = VecMath::createVector(center);
result.SphereRadius = sphereRadius;
result.BoxExtent = FVector(xs.GetAbsMax(), ys.GetAbsMax(), zs.GetAbsMax());
result.BoxExtent = FVector(maxX, maxY, maxZ);
return result;
}

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