openglplayground/VBOManager.hh

#ifndef __OPENGLPLAYGROUND_VBOMANAGER_HH__
#define __OPENGLPLAYGROUND_VBOMANAGER_HH__

#include <map>
#include <tuple>
#include <vector>
#include <list>

#include <glbinding/gl/gl.h>

using namespace gl;

class VBOManager {
public:
  VBOManager() {
  }

  ~VBOManager() {
  }

private:
  
  class VBO;

  static const size_t default_size = 1048576;
  static const size_t alignment = 8;

  class AllocFailed {};
  
public:
  class VBOAlloc {
  public:
    ~VBOAlloc() {
      if(_vbo)
	_vbo->free(*this);
      _vbo = nullptr;
    }

    VBOAlloc(VBOAlloc&& move) : _vbo(move._vbo), _ofs(move._ofs), _size(move._size) {
      move._vbo = nullptr;
    }

    VBOAlloc& operator=(VBOAlloc&& move) {
      _vbo = move._vbo;
      _ofs = move._ofs;
      _size = move._size;
      move._vbo = nullptr;
      return *this;
    }
    
    VBOAlloc() : _vbo(nullptr), _ofs(0), _size(0) {
    }
    
    size_t getOfs() const {
      assert(_vbo);
      return _ofs;
    }

    size_t getSize() const {
      assert(_vbo);
      return _size;
    }

    GLuint getVBOId() const {
      assert(_vbo);
      return _vbo->getID();
    }
    
  private:
    VBOAlloc(VBO &vbo, size_t ofs, size_t size) : _vbo(&vbo), _ofs(ofs), _size(size) {
    }

    friend class VBOManager;
    friend class VBO;
    
    VBO *_vbo;
    size_t _ofs, _size;
  };
  
  VBOAlloc alloc(size_t size, GLenum type = GL_STATIC_DRAW) {
    for(auto& vbo : _vbos[type]) {
      try {
	return vbo.alloc(size);
      } catch (AllocFailed &ex) {
	continue;
      }
    }

    _vbos[type].emplace_back((size>default_size)?size:default_size, type);
    
    return _vbos[type].back().alloc(size);
  }
  
private:

  class VBO {
  public:
    VBO(size_t size = default_size, GLenum type = GL_STATIC_DRAW) : _bufID(0) {
      glGenBuffers(1, &_bufID);
      glBindBuffer(GL_ARRAY_BUFFER, _bufID);
      glBufferData(GL_ARRAY_BUFFER, size, NULL, type);
      _allocs.emplace_back(_Entry{size, false});
    }

    VBO(VBO const& copy) = delete;

    VBO(VBO&& move) : _bufID(move._bufID), _allocs(move._allocs) {
      move._bufID = 0;
    }
    
    ~VBO() {
      for (auto ent : _allocs) {
	assert(!ent.used);
      }
      if (_bufID)
	glDeleteBuffers(1, &_bufID);
      _bufID = 0;
    }

    VBOAlloc alloc(size_t size) {
      if (size%alignment != 0)
	size += (alignment - (size%alignment));

      size_t pos = 0;
      for (auto it = _allocs.begin();it != _allocs.end();++it) {
	if (!it->used && (it->size >= size)) {
	  size_t leftover = it->size - size;
	  it->used = true;
	  it->size = size;
	  if (leftover > 0)
	    _allocs.insert(++it, _Entry{leftover, false});
	  printf("DEBUG: VBO: Allocated %lu @ %lu in %u\n", size, pos, _bufID);
	  return VBOAlloc(*this, pos, size);
	}
	pos += it->size;
      }

      throw AllocFailed();
    }

    void free(VBOAlloc& alloc) {
      size_t pos = 0;
      for (auto it = _allocs.begin();it != _allocs.end();++it) {
	if (pos == alloc._ofs) {
	  assert(it->size == alloc._size);
	  printf("DEBUG: VBO: Freed %lu @ %lu in %u\n", alloc._size, pos, _bufID);
	  it->used = false;
	  if ((std::next(it) != _allocs.end()) &&
	      !std::next(it)->used) {
	    it->size += std::next(it)->size;
	    _allocs.erase(std::next(it));
	  }
	  if ((it != _allocs.begin()) &&
	      !std::prev(it)->used) {
	    it->size += std::prev(it)->size;
	    _allocs.erase(std::prev(it));
	  }
	}
	pos += it->size;
      }
    }

    GLuint getID() const {
      return _bufID;
    }
    
  private:
    GLuint _bufID;

    struct _Entry {
      size_t size;
      bool used;
    };
    std::list<_Entry> _allocs;
    
  };
  
  std::map<GLenum, std::vector<VBO> > _vbos;
};

#endif