[Bug 89634] dEQP-GLES3: sin, cos, tan do not have enough precision

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89634

--- Comment #4 from samuel.vonstachelski at fhnw.ch ---
Hello

I came across this thread while googling why on earth the cosine in my shader
calculated wrong values.
The problem will appear as soon as a shader uses e.g. the system time for some
procedural content. I played around with a tool that works similar to
shadertoys.com, but as desktop application. There is a uniform iGlobalTime
which is generated using the system time. And the value of that uniform (aka
the time in seconds since the system started) is too high for the cosine most
time (around 13500s think). On github we also discussed this bug:
https://github.com/simon-budig/shadertoy/pull/3

Is there something happen about this issue?

>In some applications wrapping from 2π to 0 could cause artefacts due to a >discontinuity introduced in the derivative.
Ian, could you give me an example when artefacts would appear? I can not
imagine when such artefacts would appear (I guess due to my average math
knowledge).

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