.gltf model not rendering correctly

[slate nimbus]

Hi all! I've been struggling to make this model render correctly. I've attached a zip of it. It's from quixel megascans - this one (https://www.fab.com/listings/e7f99e78-4e0d-4096-8b83-7b6f21044091)

The .gltf contains multiple variations and LODs, but you can ignore them - the same problem manifests in all of them except the billboard LODs, which is that it's supposed to be a model of grass, but parts of it are not correctly transparent (see pics - rendered vs how the preview is supposed to look)

It's also showing some weird colours, which can be fixed if vertex coloring is turned off.
I suspect that either these vertex colours are supposed to be somehow interpreted as a mask so that we get the correct transparency, or one of the textures isn't getting loaded correctly, or a secret third thing - I really have no idea.

Any help would be super appreciated!

[slate nimbus]

I believe this is the texture that is supposed to define transparency

I am not sure how to interpret it though! It's called T_rbEkP_2K_ORT.png. I am guessing that stands for Opacity, Roughness, Translucency?

[slate nimbus]

I am getting a little closer

so yes, I think this is a texture that packs different information each into one channel

the opacity information is in the red channel

The Three.js texture RedFormat:

RedFormat discards the green and blue components and reads just the red component.

If I do the exact same thing to the ORT texture using imagemagick to preview what it looks like, I get this

magick Tall_Grass_rbEkP_Mid_2K_Opacity.jpg -alpha off -channel GB -evaluate set 0 +channel red-only.png

That looks almost exactly how I want! Only problem is, I can't use it as an alphaMap, because the red needs to be white

[slate nimbus]

I am super stumped. I downloaded the fbx version, which lays out the textures separately. But the opacity one is still with a red color, like the one above, and I can't figure out for the life of me how to get it to work

[slate nimbus]

The only way I was able to get it working correctly is by using the FBX version and converting the opacity texture to grayscale (manually), so that the red becomes white

[pulsar urchin]

the vertex colors for physics/wind sim in unreal.

by default three.js does
ORM (red:occ, green:rough, blue:metal) this image can be directly be plugged into AOmap, roughnessMap and metalnessMap

transparency is read from the alpha channel of the albedo/diffuse/map
and if alphaMap channel is used it only reads the green channel https://threejs.org/docs/?q=meshsta#api/en/materials/MeshStandardMaterial.alphaMap

converting the images manully is ideal since its a one time task and then its plug and play

ideal texture layout

• Color Image with transparency
• Orm image with ao , rough, metal
• Normal map in openGL format (lighting will look weird with directX)