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_arts_
12-01-2010, 04:10 PM
On the little engine I develop, when I disable texturing, the rendering is no more fast than with texturing (or very few).

But on a little program I write for my studies, using textures makes the rendering about twice slowler.

I can realize this is not done the same way (no engines in the university project), but this looks a bit big for me.

What I could thought about this is that I'm using rectangular (that can be NPOT) textures on the university project whereas in my engine I was focusing on square POT textures. I could also add that in my university project I simply use glut under Windows (so stuck with OpenGL 1.1, using no extensions at all).

What do you think about this ?

ZbuffeR
12-02-2010, 01:01 AM
You have to know a thing or two about performance.

When you have a simple program running only on a CPU, without disk access, it not always easy to follow CPU usage and understand performance.

But when you use OpenGL, it is even harder ! You have several different bottlenecks that can happen. Vsync has an effect, you can be limited by CPU, GPU vertex processing, fragment shading, or blending, etc.
So even if the texture rendering gets slower, if you are limited by CPU, rendering times will not change at all.

Also, saying "twice slower" does not mean much, as it is not additive. Measure time in milliseconds, not frame per second. There is a big difference when going from 1 to 2 milliseconds (1 ms slower), and going from 20 to 40 (20ms slower).


That being said, using NPOT texture can be slower than POT on older cards, sometimes a lot slower. You may even be forced to software rendering.
What are the technical specs of the computers ? Video card and driver version, cpu, ram, operating system ?

_arts_
12-02-2010, 02:39 AM
You're right. I was just wanting to have a discussion on it.

So the computer is:
AMD Athlon X2 2400MHz, 4 GB or RAM, ATI Mobility Radeon HD 4570, drivers not up to date (OpenGL 3.1 on Windows), Windows 7 and Debian 64.

I understand for the other parts.

What I meant with about twice slower is that without texturing the program is very fluent, and with texture it is no more (I don't know about framerate at all).

What I would like to know, so far, is, could glut, OpenGL 1.1 makes programs more slow than with GL 3.x without glut ?

Thanks.