OpenGL - Fast Textured Quads?

Question

I am trying to display as many textured quads as possible at random positions in the 3D space. In my experience so far, I cannot display even a couple of thousands of them without dropping the fps significantly under 30 (my camera movement script becomes laggy).

Right now I am following an ancient tutorial. After initializing OpenGL:

glEnable(GL_TEXTURE_2D);
glShadeModel(GL_SMOOTH);
glClearColor(0, 0, 0, 0);
glClearDepth(1.0f);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

I set the viewpoint and perspective:

glViewport(0,0,width,height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

Then I load some textures:

glGenTextures(TEXTURE_COUNT, &texture[0]);
for (int i...){
    glBindTexture(GL_TEXTURE_2D, texture[i]);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_NEAREST);
    gluBuild2DMipmaps(GL_TEXTURE_2D,3,TextureImage[0]->w,TextureImage[0]->h,GL_RGB,GL_UNSIGNED_BYTE,TextureImage[0]->pixels);
}

And finally I draw my GL_QUADS using:

glBindTexture(GL_TEXTURE_2D, q);
glTranslatef(fDistanceX,fDistanceZ,-fDistanceY); 
glBegin(GL_QUADS);
    glNormal3f(a,b,c);
    glTexCoord2f(d, e); glVertex3f(x1, y1,  z1);
    glTexCoord2f(f, g); glVertex3f(x2, y2,  z2);
    glTexCoord2f(h, k); glVertex3f(x3, y3,  z3);
    glTexCoord2f(m, n); glVertex3f(x4, y4,  z4);
glEnd();
glTranslatef(-fDistanceX,-fDistanceZ,fDistanceY);

I find all that code very self explaining. Unfortunately that way to do things is deprecated, as far as I know. I read some vague things about PBO and vertexArrays on the internet, but i did not find any tutorial on how to use them. I don't even know if these objects are suited to realize what I am trying to do here (a billion quads on the screen without a lag). Perhaps anyone here could give me a definitive suggestion, of what I should use to achieve the result? And if you happen to have one more minute of spare time, could you give me a short summary of how these functions are used (just as i did with the deprecated ones above)?

You may consider learning about display lists and Vertex Buffer Objects. — Alexandre C.
@AlexandreC. Those aren't going to help. His problem is state changes, which buffer objects and display lists don't fix. — Nicol Bolas

Nicol Bolas Nicol Bolas · Accepted Answer · 2011-10-01T21:43:05

Perhaps anyone here could give me a definitive suggestion, of what I should use to achieve the result?

What is "the result"? You have not explained very well what exactly it is that you're trying to accomplish. All you've said is that you're trying to draw a lot of textured quads. What are you trying to do with those textured quads?

For example, you seem to be creating the same texture, with the same width and height, given the same pixel data. But you store these in different texture objects. OpenGL does not know that they contain the same data. Therefore, you spend a lot of time swapping textures needlessly when you render quads.

If you're just randomly drawing them to test performance, then the question is meaningless. Such tests are pointless, because they are entirely artificial. They test only this artificial scenario where you're changing textures every time you render a quad.

Without knowing what you are trying to ultimately render, the only thing I can do is give general performance advice. In order (ie: do the first before you do the later ones):

Stop changing textures for every quad. You can package multiple images together in the same texture, then render all of the quads that use that texture at once, with only one glBindTexture call. The texture coordinates of the quad specifies which image within the texture that it uses.
Stop using glTranslate to position each individual quad. You can use it to position groups of quads, but you should do the math yourself to compute the quad's vertex positions. Once those glTranslate calls are gone, you can put multiple quads within the space of a single glBegin/glEnd pair.
Assuming that your quads are static (fixed position in model space), consider using a buffer object to store and render with your quad data.

I read some vague things about PBO and vertexArrays on the internet, but i did not find any tutorial on how to use them.

Did you try the OpenGL Wiki, which has a pretty good list of tutorials (as well as general information on OpenGL)? In the interest of full disclosure, I did write one of them.

OpenGL - Fast Textured Quads?

2 Answers