Making X report the mouse position with subpixel precision

Peter Hutterer mailinglists at
Sun Feb 25 14:43:59 PST 2007

On 24/02/2007, at 08:12 , Johan Kiviniemi wrote:
> The precision of mice is generally much better than the precision of
> screens. I'm not very familiar with the internals of X, but AFAIK it
> only reports the mouse position to clients at the screen's precision.

One of the problems I see here is that X doesn't just swallow precision.
One unit move move reported represents one pixel cursor move (+  
To have sub-pixel accuracy you need to introduce something like  
negative acceleration (e.g. 10 units mouse move == 1 pixel), causing  
the user to move the physical device around _a lot_.
> On a long page, a single pixel of scrollbar movement may cause the
> content to scroll a huge amount. The entire design of scrollbars could
> be better, but even with the current design, subpixel accuracy would
> make it easier to control the scrolling.

what is "a single pixel of scrollbar movement"? what happens when you  
hit down or move the scrollbar is decided at the application/toolkit  
level and X doesn't have anything to do with it. if you press the  
down button on a scrollbar, your app can decided to only scroll one  
pixel, if that is appropriate.

> With some recent changes, it's possible for a window to have an
> arbitrary coordinate map, to which input events are transformed. This
> allows windows to be e.g. scaled or rotated in three dimensions and
> still receive input correctly.
> Is the coordinate transformation going to happen from the screen's  
> pixel
> grid? If a window is scaled down, that would mean that all its pixels
> might not be reachable.

true but then again see first point I made.


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