Mesa *is* the open source 3D driver. If you don't want to deal with it I'm not sure how to help. It supports two different hardware layers -- generally referred to as "classic" and "gallium3D". Here are links to the mesa project, the classic hw drivers, and the gallium3D drivers :
Not sure what you mean by "portable" - if you mean one set of driver code that runs on a range of hardware generations with generation-specific code where necessary, that exists today.
The core changed radically from r5xx to r6xx (HD2xxx/HD3xxx). The 3D programming model was relatively similar between r6xx and r7xx (HD4xxx), then changed again going to Evergreen (HD5xxx) and Northern Islands (HD6xxx). The HD69xx has even more differences in the shader core, using a 4-wide VLIW instead of the 5-wide VLIW on HD24xx through HD68xx.
Last time i checked, you paid $200 for a piece of hardware. Not a guarantee that you could look up documentation online. And definitely not that said documentation wouldn't be a part of Mesa, just because "you're not interested in that". In fact, it seems everything AMD is doing, you're "not interested in". How is AMD supposed to figure out exactly what interests you?
See what i mean?
You asked about using shaders for other purposes. I provided you with proof that was already being done. You can do anything you want with these shaders.
I paid 30,000 for my car and geuss what, it came with a manual.
The sample code is added to the living driver projects in the form of initial support for each new generation of hardware.
actually gallium most likely won't have the capabilitys I am looking for. Plus I want to completely avoid the middleware becuase I'll be needing everybit of the cpu and the gpu to do what I am looking to do.