[SDL] adding wacom tablet support to sdl

[Ryan C. Gordon]

> So, I have a couple of questions. Is wacom not providing interface
> information now days? How is the device connected, USB, serial port,
> mouse port,... what? Just curiosity. I really liked the wacom tablets.
> High precision, good repeatability, easy to program for.

They either use the standard USB HID protocol, or there's a custom Linux 
driver for it...my cheap consumer-level Wacom tablet works fine on Linux 
as an evdev mouse device (has for years), and others have reported 
success with all the tilt and pressure stuff with The Gimp using XInput.

X11 itself doesn't expose the tablet-specific functionality (tilt, etc) 
outside the XInput extension, and XInput doesn't support hotplugging 
(x.org is extending XInput to handle that, though:

    http://xorg.freedesktop.org/wiki/XInputHotplug

--ryan.