Notes for ETC2/EAC sample

[shrekshao]

• etc2/eac compressed image can be in different file extension (ktx, pkm), each has a different "header data". For example, ktx file format has a header data of 68 bytes details.
• To properly handle this, we may need a so-called "texture utils". Extract the data correctly from images in different format, which can be another project.
• In this sample, I hard-coded an offset of 68 to drag the image data from the arraybuffer. Improvement can be made later.

[pjcozzi]

There is now code in Cesium to parse KTXs: CesiumGS/cesium#4758

[shrekshao]

Hmm, that is for ECT1. But I will certainly try to look into this one. It once worked on Chrome. Probably because it was some sketchy implementation at that time.

[kainino0x]

ETC2/EAC were moved into an extension shortly before the release of WebGL 2, as it has terrible performance characteristics on platforms where it's not actually supported by the hardware.

KhronosGroup/WebGL#2030

[shrekshao]

@kainino0x Thanks Kai for the clarifications. I will remove this sample from the list and leave a link to https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_etc/ in the future

[kainino0x]

Sorry, that link is outdated because the extension got renamed. Here's the correct link:

https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_etc/