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
39namespace blink {
40
41DistanceEffect::DistanceEffect()
42    : m_model(ModelInverse)
43    , m_isClamped(true)
44    , m_refDistance(1.0)
45    , m_maxDistance(10000.0)
46    , m_rolloffFactor(1.0)
47{
48}
49
50double DistanceEffect::gain(double distance)
51{
52    // don't go beyond maximum distance
53    distance = std::min(distance, m_maxDistance);
54
55    // if clamped, don't get closer than reference distance
56    if (m_isClamped)
57        distance = std::max(distance, m_refDistance);
58
59    switch (m_model) {
60    case ModelLinear:
61        return linearGain(distance);
62    case ModelInverse:
63        return inverseGain(distance);
64    case ModelExponential:
65        return exponentialGain(distance);
66    }
67    ASSERT_NOT_REACHED();
68    return 0.0;
69}
70
71double DistanceEffect::linearGain(double distance)
72{
73    // We want a gain that decreases linearly from m_refDistance to
74    // m_maxDistance. The gain is 1 at m_refDistance.
75    return (1.0 - m_rolloffFactor * (distance - m_refDistance) / (m_maxDistance - m_refDistance));
76}
77
78double DistanceEffect::inverseGain(double distance)
79{
80    return m_refDistance / (m_refDistance + m_rolloffFactor * (distance - m_refDistance));
81}
82
83double DistanceEffect::exponentialGain(double distance)
84{
85    return pow(distance / m_refDistance, -m_rolloffFactor);
86}
87
88} // namespace blink
89
90#endif // ENABLE(WEB_AUDIO)
91