Normals got flipped

[emackey]

Hi guys,

An update to BabylonJS was recently pushed to this repo (in 6a74f09), and the direction of the Y-axis on the normal maps has flipped during that update. If I load the NormalTangentTest object with the latest version of this repo, I get mixed-up normal maps, like this:

Prior to the update to BabylonJS, the same model produces correct normals:

As an experiment, I tried loading the so-called "DirectX normals" (as described in KhronosGroup/glTF#952), where the green channel intensity is inverted. These normals do produce the correct output in master on this repo, but, I believe they do not meet the glTF 2.0 spec as it stands.

[emackey]

/cc @sbtron @bghgary

[bghgary]

@emackey Thanks for catching this! I was making an optimization that inadvertently broke the generated tangents such that the handedness is wrong. I didn't notice because most of the sample models have tangents specified. I will make a fix.

[emackey]

@bghgary Great! Looking forward to merging a fix into my gltf-vscode extension.

On a related note, ThreeJS still isn't processing these normals correctly either. That bug is reported separately in donmccurdy/three-gltf-viewer#10.

[bghgary]

This should be fixed with f8f5db0

The PR for BabylonJS is here: BabylonJS/Babylon.js#2222

[emackey]

Well... I merged this into my fork, but it doesn't look like anything changed. Maybe the fix didn't get deployed to a release branch or something yet?

https://emackey.github.io/BabylonJS-glTFLoader/?model=NormalTangentTest

[bghgary]

Oops, sorry about that. I pushed the wrong version. Fixed now.

[emackey]

Awesome! Fix confirmed.