Remote Frame Buffer
That's the protocol used by VNC, so now the Wimp can be used from a VNC client, either with or without displaying to an actual display. (Keyboard support is not yet included, but the mouse works.)
To use it, set the environment variable ROLF_VNC to anything (at the moment, later it will be used to define the port to listen at and, possibly, the frame buffer resolution). If ROLF_VNC is not defined, or FRAME_BUFFER is, the proper frame buffer device will be used (rather than a shared memory bitmap).
In use, it's much faster than running the system under qemu, and I can use the host system to debug code. I'll now go back to working out the coordinate system for netsurf.