[Bug 87345] Severe noise corruption observed while running WebGL “Fluid Simulation ”

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87345

--- Comment #11 from Jason Ekstrand <jason at jlekstrand.net> ---
(In reply to qiang.miao from comment #9)
> Can't agree with you
> Why the same code can work correctly on Windows?

It works "correctly" on windows because their shader compiler probably puts
that vec2 in a different register that just so happens to be zero.  That's a
matter of luck not default values.  As matt said,

(In reply to Matt Turner from comment #10)
> The GLSL spec says "Reading a variable before writing (or initializing) it
> is legal, however the value is undefined."

Therefore, it's perfectly legal for us to give them a junk value if they don't
assign one.  Any shader that uses undefined values is a broken shader.  The
fact that it looks OK on windows is a fluke.

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