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[ Upstream commit 31c0fbf67c8c0bb38d7fb21d404ea3dbd619d99e ]
The formula of Coverage alpha blending is:
dst.a = dst.a * (0xff - src.a * SCA / 0xff) / 0xff
+ src.a * SCA / 0xff
dst.a: destination alpha
src.a: pixel alpha
SCA : plane alpha
When SCA = 0xff, the formula becomes:
dst.a = dst.a * (0xff - src.a) + src.a
This patch is to set the destination alpha (background) to 0xff:
- When dst.a = 0 (before), dst.a = src.a
- When dst.a = 0xff (after) , dst.a = 0xff * (0xff - src.a) + src.a
According to the fomula above:
- When src.a = 0 , dst.a = 0
- When src.a = 0xff, dst.a = 0xff
This two cases are just still correct. But when src.a is
between 0 and 0xff, the difference starts to appear
Fixes: 616443ca57 ("drm/mediatek: Move cmdq_reg info from struct mtk_ddp_comp to sub driver private data")
Signed-off-by: Hsiao Chien Sung <shawn.sung@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240620-igt-v3-5-a9d62d2e2c7e@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.