gluPerspective vs glOrtho

Which is faster from those primitives? I use gluPerspective and when I use glOrtho my performance dies… is this normal?

gluPerspective and glOrtho do different things. gluPerspective gives you a perspective view and glOrtho gives you an orthographic view.

gluPerspective is the glu equivalent to glFrustum. gluOrtho2d is the glu equivalent to glOrtho

[This message has been edited by Deiussum (edited 02-11-2001).]

your performance probably dies in Orthographic mode due to the fillrate.

In Perspective projection, the farther an object is from the camera, the smaller it looks, so less fillrate is needed to color it.

but in orthographic projection, the object keeps their dimensions even if they far away from the camera, so more fillrate is needed.

That’s a good idea, Gorg. However, (just to be the devil’s advocate=) even though polys are smaller when they’re further away, the perspective frustum can see MORE further away things that the ortho frustum =)


you are right John, there is a chance that the added object due to the frustum might cause a higher need of fillrate.

Didn’t think about that!

But still, I believe in most cases, the needed fillrate in Orthographic view will be higher. Also, if Z-buffering is enabled, then the number of comparisons will be higher because the region to color is bigger. It gets even worse, if you have blending on.

[This message has been edited by Gorg (edited 02-11-2001).]

Though culling should be faster in orthogonal projection, shouldn’t it?

That isn’t the cause because I DO NOT render any thing on the screen, however the performance dies. Why?

not actually DRAWING anything? Then what performance are you talking about?