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Re: [Public WebGL] extension proposal: WEBGL_compressed_texture_pvrtc






On Tue, Aug 7, 2012 at 2:42 PM, Benoit Jacob <bjacob@mozilla.com> wrote:
Hi,

This is about a new extension proposal, WEBGL_compressed_texture_pvrtc.

The pull request is there:
https://github.com/KhronosGroup/WebGL/pull/11

I've attached the generated HTML. Unfortunately Github doesn't appear to allow viewing HTML files directly off the repository.

Github requires pushing to a branch named "gh-pages" to serve live content. Currently though it seemed better to serve the live stuff from khronos.org

https://www.khronos.org/registry/webgl/extensions/proposals/WEBGL_compressed_texture_pvrtc/

 

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,
http://www.khronos.org/registry/gles/extensions/IMG/IMG_texture_compression_pvrtc.txt

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.
Benoit