Drawing Massive amounts of spheres fast ??? (q about nurbs)

[torisutan]

hi,
I'm working on drawing protein molecules, and as some of u might know, protein molecules are made up of 1000's & 1000's of atoms.

For a basic representation of these molecules, i'm just rendering each atom as a gluSphere, with 10 slices and 10 stacks.

the problem is, when the number of atoms gets large (say 8000) the frame rate drops down to less than 1 fps.

I have frustum culling, but that only helps when only a small portion of the molecule is on the screen.

i've also tried glCullFace(GL_BACK); glEnable(GL_CULL_FACE); but i can't see any difference (maybe gluSphere is handled differently?)

i've also tried to lower the number of slices/stacks depending on how close to the molecule the camera is, but as soon as the slice/stack count is less than 5, even from a distance the "spheres" don’t really look like spheres

i'm about to try use a display list for each kind of atom there is (because i plan to make each atom type a different size/color/etc).

but i was also thinking about using NURBS to draw the spheres.
however, i don't know if it's even possible to draw spheres using nurbs, and if it is possible, i was unable to make google point me to any good examples. I don't really know anything about nurbs tho, so i was wondering if anyone thinks this will help me. i assume it would create a more accurate surface, but how much extra work does the computer need to do to make them, compared to say the gluSphere?

anyways, here is the code i use to display the molecules. suggestions, comments, criticisms whatever will be greatly appreciated.
Thanks in advance
--Tristan

/* off somewhere in the init section of code */
 
	glClearColor(0.0f, 0.0f, 0.0f ,0.0f);
	glClearDepth(1.0f);
	glClearStencil(0);
 
	glShadeModel(GL_SMOOTH);
	glDepthFunc(GL_LEQUAL);
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
 
	glEnable(GL_DEPTH_TEST);
	glEnable(GL_ALPHA_TEST);
	glEnable(GL_BLEND);
 
 
	glEnable(GL_COLOR_MATERIAL);
	glEnable(GL_LIGHTING);
	glEnable(GL_LIGHT0);
 
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
/* ----------------------------------------- */
 
void OpenGLMolecule::draw()
{
 
	GLUquadric *pObj = gluNewQuadric();
	gluQuadricNormals(pObj, GL_SMOOTH);
	gluQuadricTexture(pObj, GL_TRUE);
 
	Molecule::Atom tempAtom;
 
	glColor3f(1.0f, 1.0f, 1.0f);
	glCullFace(GL_BACK);
	glEnable(GL_CULL_FACE);
	int count = 0;
	for (int i = 0 ; i < getNumberOfAtoms() ; i++)	{
		tempAtom = getAtom(i);
		if (CFrustum::getInstance()->checkSphere(tempAtom.getXpos() - origin.x, tempAtom.getYpos() - origin.y, tempAtom.getZpos() - origin.z, 1.0f))	{
			count++;
			glPushMatrix();
			glTranslatef(tempAtom.getXpos() - origin.x, tempAtom.getYpos() - origin.y, tempAtom.getZpos() - origin.z);
			gluSphere(pObj, 1.0f, 10, 10);
			glPopMatrix();
		}
	}
	glDisable(GL_CULL_FACE);
	gluDeleteQuadric(pObj);
 
}

[This message has been edited by torisutan (edited 09-05-2003).]

[mikael_aronsson]

Hi !

When the sphere is far away you might want to try to render it as antialiased GL_POINTS instead, you should alos put one sphere in a display list and render that instead each time you need a spgere, that will improve speed alot.

Using a nurb sphere works fine, but it will not help you, OpenGL (GLU) will convert the nurb surface into a sphere (triangles) anyway so it is not given you anything extra in speed.

Mikael


[This message has been edited by mikael_aronsson (edited 09-05-2003).]

[M/\dm/\n]

Textured quads + bilboard anyone?

[Mazy]

First of all i would put the gluSphere(pObj, 1.0f, 10, 10); in a displaylist atleast.. that call both calculates and renders the sphere. if you already have the triangles ready on the card you should get a huge boost.

And you dont need to have each color/size version of the sphere since glScalef and glColor can be outside the list and therefor changed for every sphere

[M/\dm/\n]

Usually you are transform bound, try to make sphere with tristrips + pull it to VBO. Small strips will give you vertex cache benefit.
But anyway, textured quad is only 4 vertices

[torisutan]

Display lists helped, i was able to get a good boost in performance. however the performance still drops down way too much as the number of spheres grows dramatically.

antialised GL_POINTS work... but are damned ugly :P
it's not worth using points until the spheres are so far away that it isn't really worth looking at the molecule. and i assume that billboarding would produce the same result.

maybe VBOs are worth a try (as M/\dm/\n suggested). does anyone have any quick links to good resources on what VBO does exactly, and how to use it? i haven't had much luck searching for "Vertex buffer object" on google

thanks again everyone
--Tristan

[bumby]

I agree with m/\dm/\n's comment about billboards. I use this technique extensively for particulate flow in a fluid simulator. I need to show thousands of objects of varying shapes and sizes, so showing 3d objects was impossible. I can show this many quads no prob ...The fps is a bit low (15-20) but this is due to the many calculations going on outside of graphics.

Jeremy

[dorbie]

Listen to the M/\dm/\n, cause the M/\dm/\n knows, but the M/\dm/\n needs to 'splain what he means by point billboarding a quad with a sphere texture.

[M/\dm/\n]

Well, all you need is to render hi-res sphere with lighting & read the rendered image (pow of 2) to texture (render to texture @ www.gametutorials.com). Then you render quad with this texture applied to it instead of sphere. Billboarding comes because this quad must be allways facing you to stay real-like. But this thing can be done quite simply by just specifying translations & leaving rotations untouched. Problems will arise if you are using camera transform, you won't escape without matrix math, tutorials again

[torisutan]

M/\dm/\n, i'll give it a go, sounds promissing. is it possible to do this using say a vertex/texture program to remove the need for glBegin() glEnd() ?? (i've heard they're quite slow??)

i don't really know anything about vertex/texture shading, but i want to learn, and if this can be done much quicker using such things i can justify the time i'll need to spend learning about them :P

thanks again
--tristan