text: //
  // Copyright (c) 2021, NVIDIA CORPORATION. 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 NVIDIA CORPORATION 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 ``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 OWNER 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.
  //
  
  #pragma once
  
  #include <sutil/sutilapi.h>
  #include <sutil/vec_math.h>
  
  
  namespace sutil {
  
  // implementing a perspective camera
  class Camera {
  public:
      SUTILAPI Camera()
          : m_eye(make_float3(1.0f)), m_lookat(make_float3(0.0f)), m_up(make_float3(0.0f, 1.0f, 0.0f)), m_fovY(35.0f), m_aspectRatio(1.0f)
      {
      }
  
      SUTILAPI Camera(const float3& eye, const float3& lookat, const float3& up, float fovY, float aspectRatio)
          : m_eye(eye), m_lookat(lookat), m_up(up), m_fovY(fovY), m_aspectRatio(aspectRatio)
      {
      }
  
      SUTILAPI float3 direction() const { return normalize(m_lookat - m_eye); }
      SUTILAPI void setDirection(const float3& dir) { m_lookat = m_eye + length(m_lookat - m_eye) * dir; }
  
      SUTILAPI const float3& eye() const { return m_eye; }
      SUTILAPI void setEye(const float3& val) { m_eye = val; }
      SUTILAPI const float3& lookat() const { return m_lookat; }
      SUTILAPI void setLookat(const float3& val) { m_lookat = val; }
      SUTILAPI const float3& up() const { return m_up; }
      SUTILAPI void setUp(const float3& val) { m_up = val; }
      SUTILAPI const float& fovY() const { return m_fovY; }
      SUTILAPI void setFovY(const float& val) { m_fovY = val; }
      SUTILAPI const float& aspectRatio() const { return m_aspectRatio; }
      SUTILAPI void setAspectRatio(const float& val) { m_aspectRatio = val; }
  
      // UVW forms an orthogonal, but not orthonormal basis!
      SUTILAPI void UVWFrame(float3& U, float3& V, float3& W) const;
  
  private:
      float3 m_eye;
      float3 m_lookat;
      float3 m_up;
      float m_fovY;
      float m_aspectRatio;
  };
  
  }
  