[Webkit-unassigned] [Bug 233817] ETC1S compressed textures don't have alpha channel information

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Fri Dec 3 12:18:28 PST 2021


https://bugs.webkit.org/show_bug.cgi?id=233817

Don McCurdy <dm at donmccurdy.com> changed:

           What    |Removed                     |Added
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                 CC|                            |dm at donmccurdy.com

--- Comment #1 from Don McCurdy <dm at donmccurdy.com> ---
This issue isn't a WebKit bug technically, although certain updates to WebKit would dramatically improve the situation.

Basis Universal ETC1S is a transmission format, and must be transcoded to something GPU-compatible on the client. In this case three.js detects that the device doesn't support ETC2 (has alpha) and so it transcodes to ETC1 (no alpha). ETC1/2 are more efficient and direct as a transcode target for ETC1S than alternatives, but lack of alpha is obviously a problem in this case. On the three.js side we should probably choose DXT as the transcode target instead, or decode to uncompressed RGBA.

That said – it would be really excellent to see Safari support the better GPU compressed texture formats that the M1 chip is capable of using! Some references:

- https://github.com/KhronosGroup/3D-Formats-Guidelines/issues/17
- https://github.com/KhronosGroup/3D-Formats-Guidelines/blob/main/KTXDeveloperGuideWebGL.md#platform-support-table

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