GLTF - Custom Image Mime Types

Yo @bghgary … Hey bro… I am trying to use custom image types .basis for my textures inside my gltf. I am making a an extension to support the .basis file offically so it wont show errors in GLTF Validation.

But… In babylon… aside from GLTF Validation warnings it still should be able to load .basis files…

But the Babylon.GLTFLoader is throwing an error when not using .png or .jpg images types…

I can tell where there error is being thrown… Is it because of the the value of image.mimeType that is being passed in _loadTextureAsync…

How can i let my custom GLTF image type of .basis work with BABYLON.GLTF.Parsing ???


There is another similar thread on this topic: Support Other Textures in GLTFLoader.

The official way to support Basis Universal in glTF is to use KTX2. See here:

I am already working on the implementations for Babylon, but they will take some time to finish as there are issues with the KTX2 libraries at the moment.

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Hey @bghgary … I been trying to following the KTX2 development.

I downloaded all the SDK and TOOLS.

I get all the way to Vulcan SDK On MacOS

But the setup instructions are not very clear. What it the the actual folder the VULCAN_SDK Custom Path is supposed to get set to…

I unzipped the whole vulcan sdk to /Users/Mackey/Vulcan folder… That is the root…

But i keep getting xcode error <vulcan/vulvan.h> file not found

I tried



None of them seems to build the ktxtools project

So i must not be setting the VULCAN SDK to the proper folder… What is the EXACT folder i should be setting VULCAN_SDK Custom Path to ???

Yo @bghgary … I think i resolved the issues…

You gotta use the KTX2 Branch and you must setup the path like so:

I got running…

I am using tool like so:

toktx --t2 --bcmp outfile.ktx2 infile.png

Seems to be making a compressed KTX2 with Basis Payload.

A couple questions:

1… Is there ANY viewer so i can view the output ktx2 file ???

2… Is there any support in babylon yet (maybe manually hacking) to load the ktx2 files ???

3… When making ktx2 compressed images… Should we ALSO keep the original .png for fallback or something… Or should re REPLACE the .png witht .ktx2… Or keep both .png and ktx2 ???

I’ve only ever built KTX-Software on a linux machine using WIndows Linux Subsystem. I think you might consider raising this issue (i.e. the instructions are not clear) on GitHub even though you got it working.

The only one I know about is here: Norbert Nopper on Twitter: "For the coders @glTF3D and @3DCommerceWG. Following tool has experimental KTX2 support:". I’ve never tried it though.

I have an local branch that can do it, but I haven’t update it in a long time, so it’s probably broken. The main issue for the web right now is that KTX-Software compiled to WASM is a huge 2MB file.

It depends. If the intent is to be a small payload, then it should be marked as required in the glTF and it will only load in clients that support the extension. It’s very similar to the Draco extension.

I talking about what extension do we put on the original GLTF texture asset… The .png or the .ktx2 ???

Will .ktx2 be specified in the KTX2_image_ext part. That way the original png loads UNLESS the gltf has the KTX2 extension… then it would be the GLTF Extension responsibility to load the alternative .ktx2 filename from its extension json and load the the .ktx2 file instead of the .png

Like the KTX extension in Babylon… You still specify the .png but you set the extension used… ie -dxt.ktx … And all calls to load that original .png are replaced by the -dxt.kxt

Is that how ktx2 is gonna work ???

From the PR I linked above: glTF/ at 74279e880b402bb9b2f4f30730beb359d8d8b060 · KhronosGroup/glTF · GitHub

You can choose to make both png and ktx2 available such that a client will load ktx2 if it supports ktx2, but a client can fallback to png if it doesn’t support ktx2. In this scenario, the extension is not required. This scenario is useful if the asset is hosted on a server somewhere as loose files so that it has the maximum compatibility without compromising on size.

The other scenario is to mark the extension as required and only put ktx2 in the asset. This is good to minimize size but sacrifices compatibility. For closed systems, this is a good choice.

In Babylon (When you get KTX2 implemented) … How will .ktx2 textures be used ???

var myTexture = new BABYLON.Texture("myTexture", "myCompressedTexture.ktx2" );

Will be just basically replace .png with .ktx2 and that is it ???

Or do you have to load a ktx2 texture with different params or something ???

I’ll leave it to @bghgary for a definitive answer, but I’d assume that the ktx2 texture loading should be transparent to the user, Ideally that snippet should be all that’s needed to load it :slight_smile:

Yes, except the file extension might be “.ktx” instead of “.ktx2”.

Yo @bghgary … Where is the REPO you made for Babylon that has support for rendering these new basisu ktx2 files… I wanna see what they will look like in babylon.js

I haven’t pushed it. I’m a bit reluctant to push it with the large wasm file.

In the big picture … a 2mb size increase for the core engine to be able to use super compressed basis images that would ultimately save much more than 2mb in compressed images… heck file size are almost 10 percent on some images with qlevel set to 255

Anyways the 2mb is well worth all the mb you save in super compressed images

So please… push it out … or at least send it me :blush:

Here is the branch: GitHub - bghgary/Babylon.js at gltf-ktx2

It is not finished. Use at your own risk. :slight_smile:

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