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dix: add some more documentation to ptraccel code

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Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>
Reviewed-by: Jamey Sharp <jamey@minilop.net>
Reviewed-by: Simon Thum <simon.thum@gmx.de>
This commit is contained in:
Peter Hutterer 2011-04-20 16:28:21 +10:00
parent 6b3a4cc6af
commit 70b76286db
1 changed files with 13 additions and 4 deletions
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17
dix/ptrveloc.c
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@ -548,6 +548,10 @@ GetDirection(int dx, int dy){
#define TRACKER_INDEX(s, d) (((s)->num_tracker + (s)->cur_tracker - (d)) % (s)->num_tracker)
#define TRACKER(s, d) &(s)->tracker[TRACKER_INDEX(s,d)]
/**
* Add the delta motion to each tracker, then reset the latest tracker to
* 0/0 and set it as the current one.
*/
static inline void
FeedTrackers(DeviceVelocityPtr vel, int dx, int dy, int cur_t)
{
@ -583,10 +587,11 @@ CalcTracker(const MotionTracker *tracker, int cur_t){
}
/* find the most plausible velocity. That is, the most distant
* (in time) tracker which isn't too old, beyond a linear partition,
* or simply too much off initial velocity.
* (in time) tracker which isn't too old, the movement vector was
* in the same octant, and where the velocity is within an
* acceptable range to the inital velocity.
*
* May return 0.
* @return The tracker's velocity or 0 if the above conditions are unmet
*/
static float
QueryTrackers(DeviceVelocityPtr vel, int cur_t){
@ -613,7 +618,7 @@ QueryTrackers(DeviceVelocityPtr vel, int cur_t){
* non-linearities are accounted for.
*/
dir &= tracker->dir;
if(dir == 0){
if(dir == 0){ /* we've changed octant of movement (e.g. NE → NW) */
DebugAccelF("(dix prtacc) query: no longer linear\n");
/* instead of breaking it we might also inspect the partition after,
* but actual improvement with this is probably rare. */
@ -745,6 +750,8 @@ BasicComputeAcceleration(
/**
* Compute acceleration. Takes into account averaging, nv-reset, etc.
* If the velocity has changed, an average is taken of 6 velocity factors:
* current velocity, last velocity and 4 times the average between the two.
*/
static float
ComputeAcceleration(
@ -1146,6 +1153,8 @@ acceleratePointerPredictable(
&fdx, &fdy,
(mult > 1.0f) && soften);
/* Calculate the new delta (with accel) and drop it back
* into the valuator masks */
if (dx) {
tmp = mult * fdx + dev->last.remainder[0];
/* Since it may not be apparent: lrintf() does not offer