rototiller: initial commit

This is a retro-style demo hack, demonstrating libdrm dummy buffer use for
achieving "oldskool" demo-style graphics programming on modern linux.

It's a quick and nasty hack, some effort was put into optimizing the renderer,
but the libdrm setup code is prototype quality at best, it's a spaghetti of
crap cobbled together while scrutinizing the libdrm headers until something
showed on-screen.

The amazing thing is, it actually works, and quite well at that, on my machine
anyways.

1 files changed, 42 insertions, 0 deletions

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+This is a quick little graphics hack I put together to experiment with libdrm
+and this "dumb buffer" thingy David Arlie added to the kernel back in 2011.
+
+If you're like me and miss the pre-KMS days of functional SVGAlib on linux
+where we could write purely software-rendered graphics toys like demos that
+were still beautiful and synchronized to vertical retrace without any tearing
+of flickering, there is cause to rejoice.
+
+Using libdrm and these two ioctls:
+DRM_IOCTL_MODE_CREATE_DUMB
+DRM_IOCTL_MODE_MAP_DUMB
+
+We can then mmap into our address space a 32bpp buffer that can be drawn to
+while off-screen, and submitted to the gpu for displaying in a page-flipping
+fashion, synchronized to the vertical retrace.  It's revisiting the 90s, it's
+VESA 2.0 linear frame buffers but actually supporting all our crazy native
+resolutions and abundant memory for 32bpp with page flipping.
+
+In my testing so far, this seems to work without even requiring root.
+
+The test machine is a 1.6Ghz Core2 duo w/i915 and 1400x1050 (x61s w/SXGA+), and
+rototiller64 only uses 30-40% of one core, rendering a flawless 50HZ.
+
+As for the files, they're identical, except rototiller64 writes 64-bit words at
+a time to the graphics buffer, rototiller32 writes 32-bit words at a time.  On
+the test machine 64-bit is good for a few % CPU savings.  I included the 32-bit
+version since it's simpler to read and maybe you have a 32-bit box.
+
+Before you try to run these things, realize this is direct libdrm graphics,
+it's going to compete with your X/wayland server.  Switch to a plain virtual
+console to run the program.  You don't need to quit X, just switch away from the
+X vt so it's not visible.
+
+To quit it's as simple as Ctrl-C, rototiller will otherwise run forever.
+
+Do not try switching back to X while rototiller is running, Ctrl-C it first, or
+X will get angry and exit when it tries to do drm things and can't.
+
+Your display may be left in an inconsistent state after exiting rototiller.
+Don't panic!  Just switch virtual consoles or go back to X, graphics will be
+restored.  This seems like a bug in drm to me.  It's genuine SVGAlib dejavu,
+corrupt displays and all.  BUCKETS OF NOSTALGIA