Mesa Beginning To Need Application Workarounds
OpenGL game/application workarounds aren't new in the world of the binary GPU drivers, especially on Microsoft Windows. The Windows drivers from AMD and NVIDIA contain heavy application-specific optimizations and workarounds. These workarounds are in place to provide greater performance in some OpenGL workloads by automatically tweaking the driver settings while in other cases the application-specific workarounds are to workaround bugs within a given piece of software.
The bug workarounds tend to happen when the game or application isn't written strictly to comply with the OpenGL specification or the software itself was written intentionally to be non-compliant so that it could workaround a bug (or other shortcoming) in a given driver at the time of the software shipping. The Catalyst driver also uses a static application list for determining when multi-GPU CrossFire support should be enabled.
Within the Mesa stack, developers are finally reaching that point -- for better or worse -- of needing application workarounds. Eric Anholt of Intel has posted a patch to the Mesa-dev mailing list that begins handling workarounds.
The first application Intel is attempting to address with an application-specific workaround is the Unigine Sanctuary tech demo, which needs a small change to take care of a GLSL bug in this older Unigine Engine demo for the i965 Mesa DRI driver.
Still somewhat up in the air is how to handle these application workarounds. This initial patch from Eric Anholt is lodging the application workarounds within the drirc file, which is the file commonly holding various Mesa settings that can be tweaked by users such as for the S3TC options, anti-aliasing, etc. Placing application workarounds by default in this file though will result in more systems having a drirc, since right now it's not actually too common for users to tweak the file or to even know about its existence.
Having the file external from the Mesa build makes it easier to maintain and to adjust accordingly when the software in question is fixed or other changes made, without the user needing to rebuild Mesa. Alternatively, there could be a new XML file for housing application-specific workarounds, such as is done by the AMD Catalyst Linux driver. Also being questioned is whether the software binary name should be used as the basis for determining whether to apply one of these "hacks" or whether to look at what libraries are being loaded -- so that blanket changes could be made across all games using a particular engine (for instance, if checking for a loaded Unigine library).
The current discussion over per-application workarounds via drirc begin with this mailing list message.