Thread: Speeding Up Obj Loader for OpenGL

Iv'e just got my latest project up and running, which is an .Obj loader iv'e been working on for the last few days, However it runs very slowly... like .5 fps if the object is mildly complex

This is due because I call glBegin and glEnd for every pollygon, and when there 13,500 pollygons to draw, thats alot of calls to glBegin and glEnd so my main question is this...
Is there a way to Draw Multipul Polygons without calling glBegin And glEnd For Every Single One? like some kind of seperator command

Also I havn't yet but will put in a binarey tree (as soon as i can get the thing to work) How much speed increase can i expect from putting from a linked list.

Any other tips or sugestions are VERY welcome.

In fact, glBegin/End() and all the related functions have been depreciated in openGL 3.2. They are referred to as "immediate mode" functions and you are right, with complex objects they become very cumbersome, partially due to the outrageous number of function calls required.

There are a few different ways of doing things without immediate mode. One is to use "Vertex Buffer Objects". These are kind of neat because it means placing all your vertices directly in video memory. The point of the immediate mode functions is to transfer data to the video card from normal RAM, and witness this occurs every single damn frame. So as an added advantage, with the VBO you can skip that -- nb, shuffling that data from RAM thru the processor to the video card involves some bottlenecks, such as the Front Side Bus speed. VBO's are like outrageously faster than immediate mode.

Further bonus: your code base is smaller. Disadvantage: you are going to be very steamed about the amount of re-coding your stuff that's required. It is kind of unfortunate that most GL beginner books, etc, never seem to explain that you are only learning a way, and not the way. However, if you have hit the wall with immediate mode (I imagine using stuff from model shops will do this pretty quick), you really and truly have no choice.

VBO's aren't very well documented. I was so p'offed with this by the time I got it all straight I decide to write a tutorial:

Intro to GL VBOs 1

I submitted this to the openGL forum users and had them review it, and I get a fair number of hits on it too. There are still some minor desciptive errors I need to correct (eg, "every function call in C/C++ requires a stack be created, then freed at the end." is not true), but all the actual code is fine*. It's quite a nice tutorial IMO (of course ).

If you want to look at the responses/corrections from the forum review, here's the thread:
VBO Tutorial ready for review! - OpenGL.org Discussion and Help Forums
I'm "akashiraffee". Everyone else is a curmudgeon Some (but not all) of the observations are a little off base, I believe this turned out to be because some people read part of the tutorial and then complained I didn't cover such and such or present it in it's full light -- the dynamic aspect of VBO manipulation isn't discussed until the third section.

You may also want to ask on that forum about the other alternatives to immediate mode, with which I am not familiar, altho I think VBOs are usually taken to be the best method.

* the texture loading function I use has a wee flaw but it works fine in context and is not important wrt VBO's anyway.

That only works for points, lines, triangles and quads though, not for polygons with an arbitrary number of vertices

I tryed to compile the VBO tutorial Posted above and got these errors

Does this mean my version of OpenGL does not support this? or am I missing something?

Im using DevC++ with the OpenGL Headers that come with it.

Originally Posted by Bubba

Meshes should only consist of triangles. If you are drawing polygons that are not triangulated you are doing something wrong.

Iv'e put the Mesh into quads but not triangles yet, it seemed to work with quads fine.
This is the first time iv'e ever really worked with this kinda stuff so it's a massive learning curve right now

Iv'e tryed to add VBO into my program and the speed improovement is awesome to say the least, but im getting this massive problem and im not sure why, i'm not sure how to discribe it but it's doing this (see attchment).

if you want to take a look iv'e uploaded the source codes Here

Other feedback is welcome also.

looks to me like you just have some vertices backward somewhere.

When this happens to me, I like to pretend I am actually doing 7D graphics instead of 3D. Nothing is wrong, it's your eyes are the problem.

Originally Posted by EVOEx

I was planning on looking at your code. But it's horribly unreadable, mostly due to the indentation. If you want others to read your code, make sure you indent right, at least.

Sorry about that, i'm not really sure what the norm is with code indentation koz iv'e only ever learn't from books and iv'e never really started posting my code on the net untill recently so iv'e fallin into some bad habbits,
As far as code indentation goes is it just bringing loops and conditionals out further then the rest of code like this

Code:

while()
{
//loop 1
            While()
            {
            //loop 2
            }

}

Or is there more to it then that?

Originally Posted by MK27

looks to me like you just have some vertices backward somewhere.

Yea iv'e nailed it down to an array prob, but why would the same array work in one mode but not the other do they use differernt array formats, or have i just got the wrong number in the rendering functions somewhere?

Originally Posted by MK27

When this happens to me, I like to pretend I am actually doing 7D graphics instead of 3D. Nothing is wrong, it's your eyes are the problem.

What do you mean by 7D? How does that help?