al_DistAtten.hpp

#ifndef INCLUDE_AL_DIST_ATTEN_HPP
#define INCLUDE_AL_DIST_ATTEN_HPP
 
/*  Allocore --
  Multimedia / virtual environment application class library
 
  Copyright (C) 2009. AlloSphere Research Group, Media Arts & Technology, UCSB.
  Copyright (C) 2012. The Regents of the University of California.
  All rights reserved.
 
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are met:
 
    Redistributions of source code must retain the above copyright notice,
    this list of conditions and the following disclaimer.
 
    Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.
 
    Neither the name of the University of California nor the names of its
    contributors may be used to endorse or promote products derived from
    this software without specific prior written permission.
 
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE.
 
 
  File description:
  Distance attentuation functions for calculating sound pressure levels,
  fog density, etc. within a space.
 
  File author(s):
  Lance Putnam, 2015, putnam.lance@gmail.com
*/
 
#include <math.h>
 
namespace al {
 
enum AttenuationLaw {
  ATTEN_NONE = 0,      
  ATTEN_LINEAR,        
  ATTEN_INVERSE,       
  ATTEN_INVERSE_SQUARE 
};
 
template <class T = float>
class DistAtten {
 public:
  DistAtten(T nearClip = T(0.1), T farClip = T(20),
            AttenuationLaw law = ATTEN_INVERSE, T farBias = T(0))
      : mNear(nearClip), mFar(farClip), mFarBias(farBias), mLaw(law) {
    setScale();
  }
 
  T nearClip() const { return mNear; }
 
  T farClip() const { return mFar; }
 
  T farBias() const { return mFarBias; }
 
  AttenuationLaw law() const { return mLaw; }
 
  DistAtten& law(AttenuationLaw v) {
    mLaw = v;
    return setScale();
  }
 
  DistAtten& nearClip(T v) {
    mNear = v;
    return setScale();
  }
 
  DistAtten& farClip(T v) {
    mFar = v;
    return setScale();
  }
 
  DistAtten& farBias(T v) {
    mFarBias = v;
    return setScale();
  }
 
  T attenuation(T dist) const {
    // No attenuation if below near distance
    if (dist <= mNear) return T(1);
 
    switch (mLaw) {
      case ATTEN_LINEAR:
        return dist < mFar ? T(1) - mScale * (dist - mNear) : mFarBias;
 
      case ATTEN_INVERSE:
        return mNear / (mNear + mScale * (dist - mNear));
 
      case ATTEN_INVERSE_SQUARE: {
        T nearSqr = mNear * mNear;
        return nearSqr / (nearSqr + mScale * (dist * dist - nearSqr));
      }
 
      default:
        return T(1);
    }
  }
 
 protected:
  T mNear, mFar;  // clipping planes
  T mFarBias;     // bias on far clip (linear model only)
  T mScale;
  AttenuationLaw mLaw;
 
  DistAtten& setScale() {
    switch (mLaw) {
      case ATTEN_LINEAR:
        mScale = (T(1) - mFarBias) / (mFar - mNear);
        break;
 
      // Note: For inverse laws, the attenuation factor at far clip is
      // hard-coded. For INVERSE_SQUARE, it is the square of the value for
      // INVERSE. This ensures a correct inverse power relationship.
      case ATTEN_INVERSE:
        mScale = (mNear / T(0.25) - mNear) / (mFar - mNear);
        break;
      case ATTEN_INVERSE_SQUARE: {
        T nearSqr = mNear * mNear;
        mScale = (nearSqr / T(0.25 * 0.25) - nearSqr) / (mFar * mFar - nearSqr);
      } break;
      default:
        mScale = 1;
    }
    return *this;
  }
};
 
/* Other possible attenuation laws where
 
  dN = (distance-mNearClip) / (mClipRange);
 
max/cosm:
  curve = (1.-dN)*(1.-dN);
hydrogen bond:
  curve = ((d + C) / (d*d + d + C))^2;  // e.g. C=2
sigmoid:
  curve = 1 - tanh(M_PI * dN*dN);
 
biasing:
  mAmpFar + curve*(1.-mAmpFar)
*/
 
}  // namespace al
 
#endif