Home | History | Annotate | Download | only in audio 
      1 /*
      2  * Copyright (C) 2010 Google Inc. All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  *
      8  * 1.  Redistributions of source code must retain the above copyright
      9  *     notice, this list of conditions and the following disclaimer.
     10  * 2.  Redistributions in binary form must reproduce the above copyright
     11  *     notice, this list of conditions and the following disclaimer in the
     12  *     documentation and/or other materials provided with the distribution.
     13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
     14  *     its contributors may be used to endorse or promote products derived
     15  *     from this software without specific prior written permission.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #include "config.h"
     30 
     31 #if ENABLE(WEB_AUDIO)
     32 
     33 #include "platform/audio/Distance.h"
     34 #include "wtf/Assertions.h"
     35 
     36 #include <math.h>
     37 #include <algorithm>
     38 
     39 using namespace std;
     40 
     41 namespace WebCore {
     42 
     43 DistanceEffect::DistanceEffect()
     44     : m_model(ModelInverse)
     45     , m_isClamped(true)
     46     , m_refDistance(1.0)
     47     , m_maxDistance(10000.0)
     48     , m_rolloffFactor(1.0)
     49 {
     50 }
     51 
     52 double DistanceEffect::gain(double distance)
     53 {
     54     // don't go beyond maximum distance
     55     distance = min(distance, m_maxDistance);
     56 
     57     // if clamped, don't get closer than reference distance
     58     if (m_isClamped)
     59         distance = max(distance, m_refDistance);
     60 
     61     switch (m_model) {
     62     case ModelLinear:
     63         return linearGain(distance);
     64     case ModelInverse:
     65         return inverseGain(distance);
     66     case ModelExponential:
     67         return exponentialGain(distance);
     68     }
     69     ASSERT_NOT_REACHED();
     70     return 0.0;
     71 }
     72 
     73 double DistanceEffect::linearGain(double distance)
     74 {
     75     // We want a gain that decreases linearly from m_refDistance to
     76     // m_maxDistance. The gain is 1 at m_refDistance.
     77     return (1.0 - m_rolloffFactor * (distance - m_refDistance) / (m_maxDistance - m_refDistance));
     78 }
     79 
     80 double DistanceEffect::inverseGain(double distance)
     81 {
     82     return m_refDistance / (m_refDistance + m_rolloffFactor * (distance - m_refDistance));
     83 }
     84 
     85 double DistanceEffect::exponentialGain(double distance)
     86 {
     87     return pow(distance / m_refDistance, -m_rolloffFactor);
     88 }
     89 
     90 } // namespace WebCore
     91 
     92 #endif // ENABLE(WEB_AUDIO)
     93