cursor handling and updates inside DRM

[Simon Thum]

Tiago Vignatti wrote:
> [0] https://bugs.freedesktop.org/attachment.cgi?id=17545
>     This doc says that it improves the heavy-load behavior, but I'm 
> failing to see it. Can you be more specific?
Sure.
The old code would assume mouse delta = speed. Of course, this 
assumption is valid only as long as mouse updates are equally spaced in 
time.
Under heavy load, the devices (or the kernel/whoever) would accumulate 
the delta. The old accel then uses that to accelerate. With polynomial 
accel or high accel factors, this leads to greatly exaggerated cursor 
movement. It drove me nuts so I decided to do something about it.

The new code doesn't fall for that. Admittedly there is still cursor 
jumping, but at least it jumps where you'd expect it to be.

I'll try explaining that better in the docs.

-Simon