Slow performance with loaded model (C++)

Hi guys,

There’s no doubt something obvious that is wrong with my code, but limited experience and the lack of success in google search has left me stumped.

I have created a parser that loads info from a .X file. This info is stored in a Mesh object, which has attributes:

	int num_vertices;	
	std::vector<Ver> vertices;

	int num_normals;
	std::vector<std::vector<float>> normals;

	int num_polys;
	std::vector<Poly> polys; 

A Poly is a vector which gives indices of the vertices in the Mesh attribute ‘vertices’ that form the polygon.

A Ver is a vector which stores the x, y, z locations of a vertex.

The mesh object has a view() function, that uses opengl commands to display the model.

 void Mesh::view() const

		Poly poly;
		int num_polys = Mesh::get_num_polys();
		int index;

		for (int i = 0; i < num_polys; i++)
			poly = Mesh::get_poly(i);
			for (int j = 0; j < (int)poly.vertices.size(); j++)
				index = poly.get_index(j);
				glNormal3f(Mesh::get_normal(index)[0], Mesh::get_normal(index)[1], Mesh::get_normal(index)[2]);
				glVertex3f(Mesh::get_vertex(index).get_coord()[0], Mesh::get_vertex(index).get_coord()[1], Mesh::get_vertex(index).get_coord()[2]);


get_vertex(i) and get_normal(i) both return the vertex/normal at the index i in the vectors storing all of the vertices/normals in the mesh object.

get_coord() returns a vector of the vertex coordinates
For the openGL window, I am using NeHe tutorial lesson 7, with all glaux and texture code removed.

I do the intial parse of the .X file in InitGL, and call the Mesh.view() function in DrawGLScene.

 int InitGL(GLvoid)										// All Setup For OpenGL Goes Here
	character = load_x_file("Man4k.X");

	glShadeModel(GL_SMOOTH);							// Enable Smooth Shading
	glClearColor(0.0f, 0.0f, 0.0f, 0.5f);				// Black Background
	glClearDepth(1.0f);									// Depth Buffer Setup
	glEnable(GL_DEPTH_TEST);							// Enables Depth Testing
	glDepthFunc(GL_LEQUAL);								// The Type Of Depth Testing To Do
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);	// Really Nice Perspective Calculations

	glLightfv(GL_LIGHT1, GL_AMBIENT, LightAmbient);		// Setup The Ambient Light
	glLightfv(GL_LIGHT1, GL_DIFFUSE, LightDiffuse);		// Setup The Diffuse Light
	glLightfv(GL_LIGHT1, GL_POSITION,LightPosition);	// Position The Light
	glEnable(GL_LIGHT1);								// Enable Light One
	return TRUE;										// Initialization Went OK

int DrawGLScene(GLvoid)									// Here's Where We Do All The Drawing
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	// Clear The Screen And The Depth Buffer
	glLoadIdentity();									// Reset The View



	return TRUE;										// Keep Going

The model loads fine. For those unfamiliar with NeHe lesson 7, pressing the arrow keys causes the model to spin. The problem I have is that the rotating model is shown at about 1FPS, and is using all 4GHz of my CPU. The model is around 3400 polygons. I could just reduce the polygon count until it works at a good FPS but that is hardly solving the problem.

Sorry if important info has been omitted, I thought listing the 500 line opengl code wouldn’t be well received.

I have no idea where to even start looking on this problem, any advice would be much appreciated.


things missing from your post :
1- what is your video card ? If you have no hardware acceleration, you can easily max out a CPU on a megapixel resolution.
2- is there any texturing in place in your scene, and what filtering do you use ?

Then : immediate mode is easy to use, but not good for any performance stuff. VBO is better read this :

When troubleshooting GL performance, it is interesting to check if the speed is related to rendering size.

Thanks for replying.

  1. It’s an ATI Radeon HD 5850. Is hardware acceleration automatic in OpenGL?

  2. There is no texturing in place. I am just trying to render a set of white triangles.

I am looking at the VBO info now.

The window size does not make a noticable difference in speed. What might this imply?

  1. yes, provided you have a correct graphic driver. For your ATI, you need a Catalyst driver (the full suite is not necessary), check here :
  2. even more surprising…

No hardware acceleration is often easy to spot when you are fillrate limited.

Installed the Catalyst driver which doesn’t seem to improve the situation. Although thanks for pointing this out, as I now have a multitude of extra things that my card can do lol.

What do you mean ‘fillrate limited’?

Just a simple question:

Do Mesh::get_poly(int), Mesh::get_normal(int) and Mesh::get_vertex(int) return references or copies of the data structures?

The reason for asking is that excessive copying of std::vectors is a real speed bump :slight_smile:
And from your code I can see that it’s already happening to the poly variable in the Mesh::view() function.


Datsua, it’s sometimes the simplest questions that give the best answers! Changed the functions to return references and now I can spin my models as fast as I can see!

And thankyou ZbuffeR for your help, too.