From c5bbe545c8046e61644db8a7c081a2d32898aedf Mon Sep 17 00:00:00 2001 From: Rich Geldreich Date: Tue, 26 May 2020 00:55:05 -0400 Subject: [PATCH] Update basis_spec.txt --- spec/basis_spec.txt | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/spec/basis_spec.txt b/spec/basis_spec.txt index dd1068c..6f71594 100644 --- a/spec/basis_spec.txt +++ b/spec/basis_spec.txt @@ -835,11 +835,13 @@ texture data, or it can immedately transcode the ETC1S data to another GPU textu 11.0 Alpha Channels in ETC1S Format Files ----------------------------------------- -If the ETC1S .basis file has an alpha channel, basis_file_header::m_flags will be logically OR's with +ETC1S .basis files can have optional alpha channels, stored in odd slices. If any slice needs an alpha channel, +all slices must have alpha channels. basis_file_header::m_flags will be logically OR's with cBASISHeaderFlagHasAlphaSlices. Alpha channel ETC1S files will contain two slices for each mipmap level (or face, or video frame, etc.). The even slices will contain the RGB data, and the odd slices will contain -the alpha data. A decoder can first decode the RGB data slice, then the next alpha channel slice, or it can -decode them in parallel using multithreading. +the alpha data, both stored in ETC1S format. A decoder can first decode the RGB data slice, then the next alpha +channel slice, or it can decode them in parallel using multithreading. The ETC1S green channel contains the +alpha values. 12.0 Texture Video ------------------