Created attachment 95518 [details] screenshot 3.0 Mesa 10.2.0-devel on Intel Ivybridge Mobile. Portal 2 is really dark, almost as if no light source is enabled. Works fine when using the Nvidia card, with primusrun.
That looks a lot like missing textures to me, not just that it's dark. (Portal 2 has been working fine here...) Do you have libtxc_dxtn installed? What does glxinfo | grep s3tc say?
Do you have libtxc_dxtn installed? No What does glxinfo | grep s3tc say? GL_OES_EGL_image, GL_OES_read_format, GL_S3_s3tc GL_OES_read_format, GL_S3_s3tc, GL_SGIS_generate_mipmap,
Do you have libtxc_dxtn installed? Actually I am not sure how to check for this, is that just a normal package? dpkg -l doesn't show anything that sounds like that.
Your glxinfo output shows GL_S3_s3tc, so it seems OK. The package is called libtxc-dxtn0 by the way. Do you use a 64 bit system? If yes, you should check that you have this package installed for i386 as well. It's also a good idea to get a 32bit glxinfo from somewhere (download the 32bit mesa-utils package from Debian's ftp site, and extract it).
Installing libtxc-dxtn0:i386 fixed it! Gameplay is kind of laggy, but I don't actually have to use the intel chip, so that is fine. I am on 64 bit system, but just extracting glxinfo from the package didn't work for me: I got this with ./glxinfo error while loading shared libraries: libGLEW.so.1.10: cannot open shared object file: No such file or directory
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