struct VertexDeclaration
{
//      |- RKVertex  (RKBuffer containing RKVertexDeclaration - describes channels: pos,norm,texcoord,skinning,color + sizes: float,short etc)
//                   (up to 12 channels)
};


struct Buffer
{
  size_t size;
  void*  data;
};


struct Shader
{
  const char* text;
  uint32_t state;
  uint32_t shaderId;
};


struct Material
{
  vec4f     color;
  uint32_t  flags;
  float     diffuseCoefficient;
  float     specularCoefficient;
  float     refractiveIndex; // fresnel ratio is calculated from angle and refractiveIndexes
  //parameters: lighting, uv anim/env mapping params, blending
  struct
  {
    Shader*   shader;
    Shader*   shadowShader;
    Texture*  textures[6];
  } doubleBuffered[2];
};


struct Camera
{
  mat4f matrix;
};


struct RenderLayer
{
  std::vector<GeometryChunk>  chunks;
  // chunk buffer
  Texture targetTexture;
  Texture inputTextures[16];
  Camera  customCamera;
};


struct GeometryChunk
{
  vec4f      position;    // relative to model
  vec4f      quaterinon;  // relative to model
  Material*  material;
  Buffer*    indexBuffer;
  Buffer*    vertexBuffer;
  // Render Layer pointer
  // Type - tri strip, lines, tris etc
  // Light info, sort priority, custom data
};


// Levels contain Objects
// Objects are in a hierarchy (parent and list of children)
// Objects contain a Renderable, also collision volumes
// Objects are RKTransformObjects which are RKPersistentBases, which are serializable/de-serializable named things
// A Renderable can be a model, sprite, anim, text, batched model, billboard, image, particle emitter etc

// Assume everything here is in a local coordinate system centered at 0,0,0
struct Model
{
  float radius;      // radius of bounding sphere
  vec4f size;        // bounds w,h,d (ie: center.x - w/2 -> center.x + w/2)
  std::vector<GeometryChunk> chunks;
};


// SceneObject could contain higher level things which have position
//   GameObject, Actor, Component, Entity
// SceneObject -> SpatialObject (object with position and occupies space)
//                     (occupies space -> implies only one object in a given pieces of space)
struct SpatialObject
{
  vec4f  position;    // center of object
  vec4f  quaterinon;  // object's orientation
  float  scale;       // uniform scale
  Model* model;       // model data
};


// Instead of storing vectors of objects
// Sparse pointer based octree
struct SceneOctree // SceneGraph
{
  struct SceneNode
  {
    union {
      SceneNode*     children[8] = { nullptr },
      SpatialObject* objects[8]  = { nullptr },
    };
  };
  SceneNode rootNode;
  float     resolution;

};