text: // Copyright Contributors to the OpenVDB Project
  // SPDX-License-Identifier: MPL-2.0
  
  #ifndef OPENVDB_VIEWER_RENDERMODULES_HAS_BEEN_INCLUDED
  #define OPENVDB_VIEWER_RENDERMODULES_HAS_BEEN_INCLUDED
  
  #include <openvdb/openvdb.h>
  #include <openvdb/tools/VolumeToMesh.h>
  #include <openvdb/tools/MeshToVolume.h>
  #include <openvdb/tools/PointScatter.h>
  #include <openvdb/tree/LeafManager.h>
  #include <openvdb/math/Operators.h>
  #include <string>
  #include <vector>
  
  #if defined(__APPLE__) || defined(MACOSX)
  #include <OpenGL/gl.h>
  #include <OpenGL/glu.h>
  #else
  #include <GL/gl.h>
  #include <GL/glu.h>
  #endif
  
  
  namespace openvdb_viewer {
  
  // OpenGL helper objects
  
  class BufferObject
  {
  public:
      BufferObject();
      ~BufferObject();
  
      void render() const;
  
      /// @note accepted @c primType: GL_POINTS, GL_LINE_STRIP, GL_LINE_LOOP,
      /// GL_LINES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN, GL_TRIANGLES,
      /// GL_QUAD_STRIP, GL_QUADS and GL_POLYGON
      void genIndexBuffer(const std::vector<GLuint>&, GLenum primType);
  
      void genVertexBuffer(const std::vector<GLfloat>&);
      void genNormalBuffer(const std::vector<GLfloat>&);
      void genColorBuffer(const std::vector<GLfloat>&);
  
      void clear();
  
  private:
      GLuint mVertexBuffer, mNormalBuffer, mIndexBuffer, mColorBuffer;
      GLenum mPrimType;
      GLsizei mPrimNum;
  };
  
  
  class ShaderProgram
  {
  public:
      ShaderProgram();
      ~ShaderProgram();
  
      void setVertShader(const std::string&);
      void setFragShader(const std::string&);
  
      void build();
      void build(const std::vector<GLchar*>& attributes);
  
      void startShading() const;
      void stopShading() const;
  
      void clear();
  
  private:
      GLuint mProgram, mVertShader, mFragShader;
  };
  
  
  ////////////////////////////////////////
  
  
  /// @brief interface class
  class RenderModule
  {
  public:
      virtual ~RenderModule() {}
  
      virtual void render() = 0;
  
      bool visible() { return mIsVisible; }
      void setVisible(bool b) { mIsVisible = b; }
  
  protected:
      RenderModule(): mIsVisible(true) {}
  
      bool mIsVisible;
  };
  
  
  ////////////////////////////////////////
  
  
  /// @brief Basic render module, axis gnomon and ground plane.
  class ViewportModule: public RenderModule
  {
  public:
      ViewportModule();
      ~ViewportModule() override = default;
  
      void render() override;
  
  private:
      float mAxisGnomonScale, mGroundPlaneScale;
  };
  
  
  ////////////////////////////////////////
  
  
  /// @brief Tree topology render module
  class TreeTopologyModule: public RenderModule
  {
  public:
      TreeTopologyModule(const openvdb::GridBase::ConstPtr&);
      ~TreeTopologyModule() override = default;
  
      void render() override;
  
  private:
      void init();
  
      const openvdb::GridBase::ConstPtr& mGrid;
      BufferObject mBufferObject;
      bool mIsInitialized;
      ShaderProgram mShader;
  };
  
  
  ////////////////////////////////////////
  
  
  /// @brief Module to render active voxels as points
  class VoxelModule: public RenderModule
  {
  public:
      VoxelModule(const openvdb::GridBase::ConstPtr&);
      ~VoxelModule() override = default;
  
      void render() override;
  
  private:
      void init();
  
      const openvdb::GridBase::ConstPtr& mGrid;
      BufferObject mInteriorBuffer, mSurfaceBuffer, mVectorBuffer;
      bool mIsInitialized;
      ShaderProgram mFlatShader, mSurfaceShader;
  };
  
  
  ////////////////////////////////////////
  
  
  /// @brief Surfacing render module
  class MeshModule: public RenderModule
  {
  public:
      MeshModule(const openvdb::GridBase::ConstPtr&);
      ~MeshModule() override = default;
  
      void render() override;
  
  private:
      void init();
  
      const openvdb::GridBase::ConstPtr& mGrid;
      BufferObject mBufferObject;
      bool mIsInitialized;
      ShaderProgram mShader;
  };
  
  } // namespace openvdb_viewer
  
  #endif // OPENVDB_VIEWER_RENDERMODULES_HAS_BEEN_INCLUDED
  