[Mesa-dev] [PATCH] glsl: Allow precision mismatch on dead uniform with GLSL ES 1.00 (v3)

[Tomasz Figa]

Hi Kenneth,

On Tue, Nov 7, 2017 at 8:18 AM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> On Thursday, October 19, 2017 9:02:20 PM PST Tomasz Figa wrote:
>> Hi Ian, Kenneth,
>>
>> On Wed, Sep 27, 2017 at 2:57 AM, Tomasz Figa <tfiga at chromium.org> wrote:
>> > Commit 259fc505454ea6a67aeacf6cdebf1398d9947759 added linker error for
>> > mismatching uniform precision, as required by GLES 3.0 specification and
>> > conformance test-suite.
>> >
>> > Several Android applications, including Forge of Empires, have shaders
>> > which violate this rule, on uniforms that are declared but not used
>> > further in shader code. The problem affects a big number of Android
>> > games, including ones built on top of one of the common 2D graphics
>> > engines and other GLES implementations accept this, which poses a serious
>> > application compatibility issue.
>> >
>> > Starting from GLSL ES 3.0, declarations with conflicting precision
>> > qualifiers are explicitly prohibited. However GLSL ES 1.00 does not
>> > clearly specify the behavior, except that
>> >
>> >   "Uniforms are defined to behave as if they are using the same storage in
>> >   the vertex and fragment processors and may be implemented this way.
>> >   If uniforms are used in both the vertex and fragment shaders, developers
>> >   should be warned if the precisions are different. Conversion of
>> >   precision should never be implicit."
>> >
>> > The word "used" is not clear in this context and might refer to
>> >  1) declared (same as GLES 3.x)
>> >  2) referred after post-processing, or
>> >  3) linked after all optimizations are done.
>> >
>> > Looking at existing applications, 2) or 3) seems to be widely adopted.
>> > To avoid compatibility issues, turn the error into a warning if GLSL ES
>> > version is lower than 3.0 and the data is dead in at least one of the
>> > shaders.
>> >
>> > v3:
>> >  - Add a comment explaining the behavior.
>> >  - Fix bad copy/paste in commit message (s/varyings/uniforms).
>>
>> Would you be able to take a look?
>>
>> Ian, I believe your previous NAK was due to the confusing erroneous
>> copy/paste from the freedesktop bug I made in commit message. Looking
>> at last comment from Kenneth there, we were going to go with my patch,
>> but things remained quiet after that.
>>
>> Thanks,
>> Tomasz
>
> Sorry, this completely fell off my radar.  I've gone ahead and pushed
> your patch.  Dylan also sent out Piglit tests for this case today, which
> I've reviewed.

No worries, thanks a lot!

Best regards,
Tomasz