I thought your goal was to have your program run on an older system, not that you want to have someone using an outdated tutorial to more easily modify it?

Using the glBegin style is a bad idea and completely incompatible with modern OpenGL. OpenGL 1.1 (which is the ancient version supported by the MS software renderer) already included support for client side Vertex Arrays, so you have no need for inefficient code doing 2 or 3 function calls per vertex.

Anyone who did not forget to install a graphics driver will have programs run in some better version of OpenGL.

Hodgman means that you would write your own Begin function that sets up some lists or arrays to collect vertexes etc., Vertex functions that add to those, and an End function that actually draws those primitives using modern OpenGL. So it would be your very own implementation of "legacy OpenGL" using modern OpenGL.

I understand now, that could be an approach.

Is the program actually required to run on machines with very old GPU and drivers that only support GL1.x, no shaders etc. or is it just that you want to supply a legacy OpenGL style API for users of the program?

It is the very old GPU / drivers, not the API style it self.

I thought your goal was to have your program run on an older system, not that you want to have someone using an outdated tutorial to more easily modify it?

Using the glBegin style is a bad idea and completely incompatible with modern OpenGL. OpenGL 1.1 (which is the ancient version supported by the MS software renderer) already included support for client side Vertex Arrays, so you have no need for inefficient code doing 2 or 3 function calls per vertex.

Anyone who did not forget to install a graphics driver will have programs run in some better version of OpenGL.

That can be another possibility, using vertex arrays. I will learn about it.

Thanks all.

You should find out exactly which version with which extensions you have available, not just assume the oldest.

You could try the extensions viewer at http://www.realtech-vr.com/glview/ which should show you everything, the OpenGL version and all extensions your computer supports.

Then use the least old version that runs after updating your graphics drivers.

Thanks again for the suggestions, I believe I come with a solution that will work for me.

First to clarify, from a point of view of the old support, I just need that old materials (ambient color, specular color) with triangles(normals, color per vertex) with that simple gouraud shading. So that is something supported since the very beginning of openGL I believe. No extensions are planned. Visuals and speed are not a concern.

With the help of your suggestions I come with the idea to use Vertex Arrays (glDrawArrays or the interleaved ) so it will be the same vertex structure for the two modes, then, I must design some "engine" using OOP that will abstract (and simplify) the use and display of models (material + mesh) and then implement it specific for the two modes.

I must create some abstraction for camera position, load of the models, display (based in some position / scale / transformation) etc..

Let me know if you know about some libraries that implement something similar.

Thanks.

It is the very old GPU / drivers, not the API style it self.

This is something that comes up a couple of times a year.

I'd caution you to be absolutely certain that the hardware you're targetting is still actually in use before imposing this limitation on yourself. Have you researched your target audience or are you working from gut feeling/personal preference here? Because nowadays "very old hardware" can have multiple meanings and they may be surprising.

Hi mhagain,

This evaluation will be for an opensource EDA CAD tool (Kicad) for the 3D visualization mode. That is a type of tool that can be used in schools and universities.

We have a report that in a high school in Italy (Europe), they still have for example 50% 15 year old Pentium IV in their labs.

We have also reports from users that are using the application in machines with cards:
Ati Radeon 9550 128 mb (2004 - 11 yrs old)

Nvidia 5200 128mb (2003 - 12 yrs old)

GeForce 9500GT (2008 - 7 yrs old)

Intel GM945 (2006 - 9 yrs old)

In this cases (special in the schools), we cannot assume that they are running updated drivers or the vendor drivers. So the idea to support the very basic openGL is to provide always some kind of 'safe mode' for this cases.

I guess these are just "interested" people, not actual current users? Its likely they forget about it and never use it.

Have you thought about how long it would take you to complete the program? When its finally done most of these older computers that currently exist will have been thrown away.

If these people then are really interested in your program they have to go to the effort of installing the necessary drivers. You probably don't want to put months of extra work into supporting people too lazy to do that?