1 files changed, 95 insertions, 0 deletions
diff --git a/src/python/filter.py b/src/python/filter.py
new file mode 100644
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+++ b/src/python/filter.py
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+# -*- coding: utf-8 -*-
+# libavg - Media Playback Engine.
+# Copyright (C) 2003-2014 Ulrich von Zadow
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+# Current versions can be found at www.libavg.de
+#
+
+import math
+
+# Input filter based on:
+# Casiez, G., Roussel, N. and Vogel, D. (2012). 1€ Filter: A Simple Speed-based Low-pass
+# Filter for Noisy Input in Interactive Systems. Proceedings of the ACM Conference on
+# Human Factors in Computing Systems (CHI '12). Austin, Texas (May 5-12, 2012). New York:
+# ACM Press, pp. 2527-2530.
+
+class LowPassFilter(object):
+
+    def __init__(self, alpha):
+        self.__setAlpha(alpha)
+        self.__y = None
+        self.__s = None
+
+    def __setAlpha(self, alpha):
+        alpha = float(alpha)
+        if alpha <= 0 or alpha > 1.0:
+            raise RuntimeError("LowPassFilter alpha (%s) should be in (0.0, 1.0]"%alpha)
+        self.__alpha = alpha
+
+    def apply(self, value, timestamp=None, alpha=None):        
+        if alpha is not None:
+            self.__setAlpha(alpha)
+        if self.__y is None:
+            s = value
+        else:
+            s = self.__alpha*value + (1.0-self.__alpha)*self.__s
+        self.__y = value
+        self.__s = s
+        return s
+
+    def lastValue(self):
+        return self.__y
+
+
+class OneEuroFilter(object):
+
+    def __init__(self, mincutoff=1.0, beta=0.0, dcutoff=1.0):
+        if mincutoff<=0:
+            raise ValueError("mincutoff should be >0")
+        if dcutoff<=0:
+            raise ValueError("dcutoff should be >0")
+        self.__freq = 60     # Initial freq, updated as soon as we have > 1 sample
+        self.__mincutoff = float(mincutoff)
+        self.__beta = float(beta)
+        self.__dcutoff = float(dcutoff)
+        self.__x = LowPassFilter(self.__alpha(self.__mincutoff))
+        self.__dx = LowPassFilter(self.__alpha(self.__dcutoff))
+        self.__lasttime = None
+        
+    def __alpha(self, cutoff):
+        te    = 1.0 / self.__freq
+        tau   = 1.0 / (2*math.pi*cutoff)
+        return  1.0 / (1.0 + tau/te)
+
+    def apply(self, x, timestamp):
+        timestamp /= 1000.
+        if self.__lasttime == timestamp:
+            return x
+        else:
+            # ---- update the sampling frequency based on timestamps
+            if self.__lasttime and timestamp:
+                self.__freq = 1.0 / (timestamp-self.__lasttime)
+            self.__lasttime = timestamp
+            # ---- estimate the current variation per second
+            prev_x = self.__x.lastValue()
+            dx = 0.0 if prev_x is None else (x-prev_x)*self.__freq # FIXME: 0.0 or value?
+            edx = self.__dx.apply(dx, timestamp, alpha=self.__alpha(self.__dcutoff))
+            # ---- use it to update the cutoff frequency
+            cutoff = self.__mincutoff + self.__beta*math.fabs(edx)
+            # ---- filter the given value
+            return self.__x.apply(x, timestamp, alpha=self.__alpha(cutoff))
+