This is about a new extension proposal, WEBGL_compressed_texture_pvrtc.
The pull request is there:
I've attached the generated HTML. Unfortunately Github doesn't appear to allow viewing HTML files directly off the repository.
The need for mobile compressed texture formats is real. This is the #1 thing we're being asked for my game developers regarding Web games on mobile devices.
Also, while I understand that ETC2 is coming, we need something that will help WebGL take off on today's mobile devices.
This extension stays close to the corresponding OpenGL ES extension,
In particular, the power-of-two and texSubImage-must-replace-the-whole-image requirements come from there.
You might notice that the formulas for butter byte length are looking different: for the 2bpp formats, the OpenGL ES extension has
( max(width, 16) * max(height, 8) * 2 + 7) / 8
whereas the WebGL extension proposal has
max(width, 16) * max(height, 8) / 4
The two formulas are in fact equivalent, given that width and height must be powers of two. The latter formula is just a simplification taking advantage of this fact.
Please, consider it for promotion to draft status so that implementation can start.