dix/xfree86: simplified velocity approximation algorithm

Replace multi-stage filtering with simple linear velocity,
tracked several instances backwards. A heuristic ensures
only approximately linear motion is considered, so velocity
remains valid in any case. Numerical stability is much
better, and nothing changes to people who didn't tune the
advanced features of the previous algorithm.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

1 files changed, 19 insertions, 30 deletions

diff --git a/include/ptrveloc.h b/include/ptrveloc.h
index f9933c98a..6ef8c754e 100644
--- a/include/ptrveloc.h
+++ b/include/ptrveloc.h
@@ -27,11 +27,6 @@
 
 #include <input.h> /* DeviceIntPtr */
 
-/* maximum number of filters to approximate velocity.
- * ABI-breaker!
- */
-#define MAX_VELOCITY_FILTERS 8
-
 /* constants for acceleration profiles;
  * see  */
 
@@ -57,46 +52,41 @@ typedef float (*PointerAccelerationProfileFunc)
                float /*velocity*/, float /*threshold*/, float /*acc*/);
 
 /**
- * a filter stage contains the data for adaptive IIR filtering.
- * To improve results, one may run several parallel filters
- * which have different decays. Since more integration means more
- * delay, a given filter only does good matches in a specific phase of
- * a stroke.
- *
- * Basically, the coupling feature makes one filter fairly enough,
- * so that is the default.
+ * a motion history, with just enough information to
+ * calc mean velocity and decide which motion was along
+ * a more or less straight line
  */
-typedef struct _FilterStage {
-    float*  fading_lut;     /* lookup for adaptive IIR filter */
-    int     fading_lut_size; /* size of lookup table */
-    float   rdecay;     /* reciprocal weighting halflife in ms */
-    float   current;
-} FilterStage, *FilterStagePtr;
+typedef struct _MotionTracker {
+    int dx, dy;     /* accumulated delta for each axis */
+    int time;         /* time of creation */
+    int dir;        /* initial direction bitfield */
+} MotionTracker, *MotionTrackerPtr;
 
 /**
  * Contains all data needed to implement mouse ballistics
  */
 typedef struct _DeviceVelocityRec {
-    FilterStage filters[MAX_VELOCITY_FILTERS];
+    MotionTrackerPtr tracker;
+    int num_tracker;
+    int cur_tracker;        /* current index */
     float   velocity;       /* velocity as guessed by algorithm */
     float   last_velocity;  /* previous velocity estimate */
-    int     lrm_time;       /* time the last motion event was processed  */
-    int     last_dx, last_dy; /* last motion delta */
-    int     last_diff;      /* last time-difference */
-    int     last_phase;     /* phase of last/current estimate */
+    int     last_dx;      /* last time-difference */
+    int     last_dy ;     /* phase of last/current estimate */
     float   corr_mul;       /* config: multiply this into velocity */
     float   const_acceleration;  /* config: (recipr.) const deceleration */
     float   min_acceleration;    /* config: minimum acceleration */
     short   reset_time;     /* config: reset non-visible state after # ms */
     short   use_softening;  /* config: use softening of mouse values */
-    float   coupling;       /* config: max. divergence before coupling */
+    float   max_rel_diff;   /* config: max. relative difference */
+    float   max_diff;       /* config: max. difference */
+    int     initial_range;  /* config: max. offset used as initial velocity */
     Bool    average_accel;  /* config: average acceleration over velocity */
     PointerAccelerationProfileFunc Profile;
     PointerAccelerationProfileFunc deviceSpecificProfile;
     void*   profile_private;/* extended data, see  SetAccelerationProfile() */
     struct {   /* to be able to query this information */
         int     profile_number;
-        int     filter_usecount[MAX_VELOCITY_FILTERS +1];
     } statistics;
 } DeviceVelocityRec, *DeviceVelocityPtr;
 
@@ -104,13 +94,12 @@ typedef struct _DeviceVelocityRec {
 extern _X_EXPORT void
 InitVelocityData(DeviceVelocityPtr s);
 
+extern _X_EXPORT void
+InitTrackers(DeviceVelocityPtr s, int ntracker);
+
 extern _X_EXPORT BOOL
 InitializePredictableAccelerationProperties(DeviceIntPtr pDev);
 
-extern _X_EXPORT void
-InitFilterChain(DeviceVelocityPtr s, float rdecay, float degression,
-                int lutsize, int stages);
-
 extern _X_EXPORT int
 SetAccelerationProfile(DeviceVelocityPtr s, int profile_num);