upgrade to 13.4: wrong/strange behavior opengl es vertex shader

[wim de vries]

Graphics: Intel® 965GM
I suspect (I am not a mesa etc. specialist) sth wrong in the mesa lib, because opengl ES isn't working correctly any more.
I had a WebGL app running nicely in FireFox and Chromium (Ubuntu 12.10).
I upgraded from 12.10(64bits) to 13.4 (64bits).
Now it does not work correctly any more in FireFox as well as Chromium.
No errors, but serious wrong behavior.
It still works correctly on other machines (ubuntu 12.04/FireFox, macBook/FireFox, windows/Chromium).
The bug turns up in the following lines of the vertex shader (coming from javascript/WebGL)
-----------
uniform mediump vec3 criticalHeights;
attribute mediump vec3 vertex;
...
if(criticalHeights[2] > vertex.z )
    {varAmbientLight = redAmbientLight; varDiffuseLight = redDiffuseLight;};
     }
-----------
criticalHeights[2] and vertex.z vary between -100 and + a few hundred.
the 'if' statement always returns true, even with extreme values like -1000000.0 < vertex.z or criticalHeights[2] > 1000000.0
Please find attached output of glxinfo.
Thanks.

[wim de vries (wsvries)]

Just tested an existing desktop Qt opengl ES application, with same kind of code (if ...).
Also same wrong behaviour.

[Oibaf (oibaf)]

The used Ubuntu version is no longer supported, can you check if the problem is still reproducible on a newer Ubuntu?

[Launchpad Janitor (janitor)]

[Expired for mesa (Ubuntu) because there has been no activity for 60 days.]