Hi.

I'm making a voxel world renderer to learn OpenGL. I divided the world in Chunks (group of blocks/voxels) and I thought that the rendering could be optimized if only one draw call was done per chunk, instead of one draw call per block. The problem is that I don't know how to add vertices to the VBO, and I don't think it is possible. I'm learning OpenGL with this wikibook : http://en.wikibooks.org/wiki/OpenGL_Programming but it only shows how to use VBOs for a known number of vertices (a single cube for example). Is there a way to add vertices to a VBO ?

Or if that's not possible, is there a way to create a mesh and add triangles or vertices to it and then display it ?

I'm sorry if this question has already been asked, I couldn't find what I wanted to know.

Thanks a lot.

You can change the content of a buffer in various ways, for example by calling glBufferSubData or by mapping the content to memory with glMapBuffer. If your buffer content can change in size, then start with a large buffer and draw only the necessary part of it so you can expand it later when needed without having to relocate the entire buffer.

Thanks a lot everybody, so what I did is that i stock each triangle in a 4D vector (using glm::tvec4<GLbyte>) where the 4th dimension is used for the color of the triangle.

But I have a problem, not with this thing particularly, I think, but nothing is drawn on the screen.

Here's how my code is structured:

main.cpp

int main(int ac, char **av)
{
	g_window = new Renderer;
	g_window->init(ac, av);
	g_window->createWindow(vector2i(500, 0), vector2i(1280, 720), "OpenGL");
	if (g_window->resources())
	{
		glutDisplayFunc(onDisplay);
		glutReshapeFunc(onReshape);
		glutIdleFunc(onIdle);
		glutSpecialFunc(onSpecial);
		glutSpecialUpFunc(onSpecialUp);
		glutIdleFunc(onDisplay);
		glutPassiveMotionFunc(onMotion);
		glutMotionFunc(onMotion);
		glutMainLoop();
	}
	delete (g_window);
	return (0);
}

Renderer.cpp

/* Constructor, destructor and other methods */

void Renderer::createWindow(vector2i winPos, vector2i winSize, const char *winTitle)
{
	this->_winSize = winSize;
	glutInitWindowPosition(winPos.x, winPos.y);
	glutInitWindowSize(this->_winSize.x, this->_winSize.y);
	glutCreateWindow(winTitle);
        this->_chunks.push_back(new Chunk);
	this->_chunks.at(0)->createMesh();
	if (glewInit() != GLEW_OK)
	{
		std::cout << "glewInit failed" << std::endl;
		exit(1);
	}
	if (glewIsSupported("GL_VERSION_4_5"))
		std::cout << "GLEW Version is 4.5" << std::endl;
	else
		std::cout << "GLEW 4.5 not supported" << std::endl;
}

bool Renderer::resources()
{
	this->_program = createProgram("cube.v.glsl", "cube.f.glsl");
	if (this->_program == 0)
		return (false);
	this->_attribute_coord = glGetAttribLocation(this->_program, "coord");
	if (this->_attribute_coord == -1)
	{
		std::cerr << "Could not bind attribute coord3d." << std::endl;
		return (false);
	}
	this->_uniform_mvp = glGetUniformLocation(this->_program, "mvp");
	if (this->_uniform_mvp == -1)
	{
		std::cerr << "Could not bind attribute mvp." << std::endl;
		return (false);
	}
	glUseProgram(this->_program);
	glEnableVertexAttribArray(this->_attribute_coord);
	return (true);
}

void Renderer::beginScene() const
{
	glm::mat4 view = glm::lookAt(this->_position, this->_position + this->_lookAt, glm::vec3(0, 1, 0));
	glm::mat4 projection = glm::perspective(45.0f, 1.0f * this->_winSize.x / this->_winSize.y, 0.01f, 1000.0f);
	glm::mat4 mvp = projection * view;
	glUniformMatrix4fv(this->_uniform_mvp, 1, GL_FALSE, glm::value_ptr(mvp));
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}

void Renderer::endScene() const
{
	glutSwapBuffers();
}

void Renderer::onDisplay()
{
	this->beginScene();
	this->renderChunks();
	this->endScene();
}

void Renderer::renderChunks()
{
	int i;

	i = -1;
	while (++i < this->_chunks.size())
	{
		this->_chunks.at(i)->render(this->_attribute_coord);
	}
}
/* And others method for mouse movement etc */

Chunk.cpp

void Chunk::render(GLint attribute_coord)
{
	if (!this->_currentVertex)
		return;
	glBindBuffer(GL_ARRAY_BUFFER, this->_vbo);
	glVertexAttribPointer(attribute_coord, 4, GL_BYTE, GL_FALSE, 0, 0);
	glDrawArrays(GL_TRIANGLES, 0, this->_currentVertex);
}

So Renderer is a class I made that contains everything needed for rendering, such as the program for the shaders etc.

I'm a begginer in OpenGL and I don't know where the problem is.

Thanks for helping me!

EDIT: Sorry if i wasn't clear in the first post, what i wanted wasn't a trick to resize a VBO but just to add vertices to it (just once, at the creation of it).