I just checked and Minecraft can indeed run on LLVMpipe… it runs on swrast as well but its quite broken in my install as is i915g. i915 itself works great though getting aout 25-30fps whereas LLVMpipe gets about 10-15 with few flucuations in fps. Note that 10-15 FPS is about 1.5x-2x better than an Nvidia Geforce2 can muster just for reference. I would imagine I could limit fps and still be quite playable.
Its VERY playable on my i7 3630qm w/ 1600Mhz ram, its an 11.6in netbook with an i7 NP6110 or W110ER depending on who you ask its very awesome and runs both Funtoo with E17 and Haiku great! The fan does kick in pretty loud though when running on LLVMpipe unlike either GPU (I have intel 4000HD I usually use, and also an Nvidia 650m that runs about 2x as fast with bumblebee/primus).
I did some further testing while writing this. To summarize.
1.2Ghz 2 threads 2-3fps/4-5 windowed completely silent
2.4Ghz 1 thread 7-8 fps fullscreen this is fairly silent fan comes on intermitently
2.4Ghz 8 threads 10-14 fps fullscreen pretty loud fan constantly but its pretty responsive in game as well probably since minecraft itself is running faster.
I can go up to about 2Ghz silet with 8 threads and its running about 8-10fps I hear the fan very faintly… larger laptops probably won’t have any trouble running up to 2.2 Ghz I imagine without any fan.
To perform that test I just moved the driver libraries into a backup folder for while I tested LLVMpipe and I set the thread with LP_NUM_THREADS=8 java -jar minecraft.jar