Draco exports have wrong mesh bounds at export

[anonymous2585]

Describe the bug
When exporting a mesh using draco compression, the mesh bounds written in the file is inverted on the X axis.

File
OffsetCube.zip

To Reproduce

• Export a mesh that has its pivot far from the verticies on the x axis
• Import the mesh at runtime (do not call Mesh.RecalculateBounds on the mesh after importing)
• Move the camera in 3D space

See the object been culled by Unity even when still in view.

Expected behavior
The bounding box is correct and user doesn't need to use Mesh.RecalculateBounds to fix the mesh bounds.

Proposed fix
We fixed this issue locally by adding a - here:

glTFast/Runtime/Scripts/Export/GltfWriter.cs

Line 1213 in ef121f3

center.x-extents.x,

(changed to -center.x-extents.x,)

And here:

glTFast/Runtime/Scripts/Export/GltfWriter.cs

Line 1219 in ef121f3

center.x+extents.x,

(changed to -center.x+extents.x,)

If you look at the legacy export, there is the - sign on X axis:

glTFast/Runtime/Scripts/Export/GltfWriter.cs

Line 1389 in ef121f3

accessor.max = new[] { -min.x, max.y, max.z };

so we think it has been forgotten in the draco code.

Setup

• glTFast version 6.3.0
• Unity Editor version 2023.2.20f1
• Render Pipeline: build-in
• Platform: Windows editor

[anonymous2585]

@atteneder Can you please take a look at this issue? It affects people using draco exports, and the fix seems pretty easy.

[atteneder]

@anonymous2585 Great find and excellent report! The fix will land in one of the upcoming updates.