BIG DOG — now with a compiled renderer.

    bigdog          play it (SPACE or W flaps)
    bigdog-demo     let it fly itself

WHAT CHANGED
The game logic is still Tcl. The pixels are not: /bin/fbdraw is a static
wasm32 C binary that owns /dev/fb0, and Tcl describes each frame to it as a
few dozen command lines over a pipe.

Measured in one boot, 300 frames, 480x320:

    home/bigdog.tcl          (Tcl draws every pixel)   602 ms/frame
    home/bigdog-fbdraw.tcl   (fbdraw renders)          2.1 ms/frame

The old one was never limited by the framebuffer — the device does 367 MB/s.
It was limited by an interpreter touching pixels one list element at a time.

WHY IT IS FAST
mmap(/dev/fb0) fails ENODEV here, and pwrite64 is ENOSYS on the wasm32
syscall table, so a frame costs lseek+write syscalls. fbdraw keeps the last
flushed frame and writes only rows that actually changed; a dog crossing a
static sky dirties a fraction of the screen and the rest cost a memcmp.

Source: demos/bigdog-fbdraw.tcl and packages/custom/fbdraw/fbdraw.c