Bug 9156

Summary:	Mouse acceleration doesn't work properly
Product:	xorg	Reporter:	Simon Thum <simon.thum>
Component:	Input/Mouse	Assignee:	Xorg Project Team <xorg-team>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	high	CC:	avery
Version:	git
Hardware:	x86 (IA32)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Bug Depends on:
Bug Blocks:	8583

Description Simon Thum 2006-11-25 11:48:15 UTC

In current git, the polynomial acceleration obtained by e.g.
>xset n 0
is broken. Slow movements are often discarded, as if no movement took place.
I noted when doing bug#8583 so I can tell (most probably) it shows up if the
acceleration function does actually decelerate, as is the case on slow moves.

Comment 1 Simon Thum 2006-11-29 15:30:02 UTC

The behaviour was caused by wrong int/float conversions.
I'll fix in bug#8583.

Comment 2 Adam Jackson 2008-02-24 18:23:50 UTC

Mass reopen.  The "REMIND" resolution is lame, I'm deleting it.  Consider yourself reminded.

Comment 3 Peter Hutterer 2008-04-23 21:35:47 UTC

(In reply to comment #1)
> The behaviour was caused by wrong int/float conversions.
> I'll fix in bug#8583.

Simon:
do you have a patch that can be applied to current master to fix this? 8583 is a bit too excessive for now.

Comment 4 Daniel Stone 2008-05-16 09:52:31 UTC

dropping from 1.4.1 blocker, as #8353's fix is a bit too invasive.

Comment 5 Simon Thum 2008-05-17 09:44:16 UTC

The fix is just a one-word exchange in inputstr.h:

typedef struct _ValuatorClassRec {
...
    float                 dxremaind, dyremaind; /* for acceleration */
...
} ValuatorClassRec, *ValuatorClassPtr;

In my tests that was all it took and it should be ABI-compatible as long as no one actually reads those fields (except the server) plus the platform has identical alignment and size for int/float.

IMHO it's feasible, and it just restores the state it had before hotplug (I guess; dunno who actually changed it or why).

Comment 6 Avery Fay 2008-05-21 23:12:55 UTC

As a user, I'd like to see this fix (actually, 8583 looks even better, but I realize it's a more extensive change). "xset m n 0" definitely feels the best, but I can literally move my mouse across the whole mousepad (slowly) without moving at all on screen.

Comment 7 Peter Hutterer 2008-05-22 01:24:24 UTC

On Sat, May 17, 2008 at 09:44:16AM -0700, bugzilla-daemon@freedesktop.org wrote:
> --- Comment #5 from Simon Thum <simon.thum@gmx.de>  2008-05-17 09:44:16 PST ---
> The fix is just a one-word exchange in inputstr.h:
> 
> typedef struct _ValuatorClassRec {
> ...
>     float                 dxremaind, dyremaind; /* for acceleration */
> ...
> } ValuatorClassRec, *ValuatorClassPtr;
> 
> In my tests that was all it took and it should be ABI-compatible as long as no
> one actually reads those fields (except the server) plus the platform has
> identical alignment and size for int/float.

Unfortunately it isn't. Drivers have access to the valuator struct, so it must
be considered as an ABI change.

Comment 8 Simon Thum 2008-05-22 15:21:34 UTC

(In reply to comment #7)
> Unfortunately it isn't. Drivers have access to the valuator struct, so it must
> be considered as an ABI change.
Correct. But it may well be an ABI break without victims.

driver # grep dxremaind -R *
gave me no source matches (though many binary ones). I'd guess that other things cause more end-user breakage.

Comment 9 Peter Hutterer 2008-05-26 22:54:25 UTC

Pushed to git master as 0050165a67bb462e0bf644a11644ad9d587c62bb.

Comment 10 Adam Jackson 2008-07-01 07:12:24 UTC

Also cherrypicked to 1.5 branch.

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