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Thread: A quote from - Mark J. Kilgard Principal System Software Engineer nVidia

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  1. #11
    Junior Member Newbie
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    Jun 2013
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    Personally, I'm a firm believer in encouraging new people to use the most painless, easy to use and configure API features available and they will have the best chance of succeeding, especially if they don't need fancy-pants methods.

    Except for the dangers of unavoidable situations like the OpenGL ES 2.0 spec which severed the incredibly valuable link between the old and the new. Those devices support both, however those machines have such tight memory space and bandwidth constraints that this unfortunate situation is understandable and necessary.
    Yes it is absolutely absurd to expect mobile devices to have 100 MB+ drivers packages that would allow for a robust and fully-featured OpenGL environment... for now!

    In the future this is likely going to happen and they will soon all be able to give the Dynamic Duo of desktop machines a run for their money in shear diversity of API combinations available.

    Please don't get me wrong here! Bang, exclamation point. In no way shape or form should any present or future development be made on 'immediate mode." That would be like carpenters investing time and money into developing new types of screws. There would be no point.

    The nVidia documents that stongly indicates that no legacy features will be removed also state that no future consideration will be given to them. They have already been optimized and tested and refined. They will take up nobody else's time. There is no concern that research time and effort are being wasted on that stuff. They are not reinventing the wheel over and over again with legacy code. That legacy code ran on machines that are nothing but pocket watches compared to machines today. There is no way that stuff is running slower now than it did on crappy, old machines.

    Legacy has not caught up in sheer raw, large scale performance, so what, why use a car in a situation where a bicycle will do?. Legacy will not go anywhere unless it is specifically conflicting with modern functions. Why should it? It takes me 5 minutes to download the absurdly large driver packages.

    If you want to eliminate bugs from your code, the best way to do it is to always test your software on as many GPU's as possible, as often as possible. I keep two old junk laptops on hand for this very purpose. One is a very old, and very weak, x1150 mobile Radeon that my friend's girlfriend spilled juice on. The drivers for that machine are buggy to begin with. I know that if it runs on that machine then it will run on almost any computer that is newer than 5 years old.

    I also keep a mobile Intel GPU machine that was made right when Intel finally caught up with ATI/nVidia shader model 2.0/3.0 hardware. I also know that if it works on this then it will work on everything without any fear of bugs creeping in on someone else's computer.

    I also test using the WINE emulator on a regular basis when I've been making substantial changes using features that behave differently under different circumstances.

    Using newer features such as floating point textures is a poop-field so far as truly cross-platform goes. What works beautifully on some cards cannot be implemented properly on another made by someone else.

    To resolve this issue, we all have to work together to build a cheat-sheet that has input from hundreds of people that has all been tested on hundreds of machine configurations. Either that or we have to wait for the various manufactures to play catch-up with one another. We can wait for them to do it or we can do it ourselves. Then people will be able to use it safely and reliably, and the GPU maunfacturers will have clear, documented evidence that will help them eliminate bugs in their drivers and circuits.

    OpenGL 4.0+ currently has a big problem since a five stage shader and all the accompanying features have a lot of kinks to be worked out. Most people that come here do not have huge teams of software designers and testers at their disposal to get this working consistently across many platforms.
    We have to do this ourselves or there will once again be huge repositories of bug ridden code several years from now.

    It would be better if we make listings of people's efforts with trial and error. Under many different circumstances.

    For instance, "Which newer extensions are giving people problems, and on which machines?"
    and also, "Which of the newer extensions are known to work consistently on all available platforms?"

    If we create a repository of these basic facts then we will have helped to resolve this issue of GPU manufacturers being unwilling to share results with one another.

    Bug testing something as seemingly simple as a floating point texture is out of the reach of most people since there are no reliable threads where people have listed what is working for them and what is not. The old standard of people listing their machine specs has all but disappeared. That's probably a good thing since I used to think these forums were nothing but horrible hardware and API flame-wars. This has changed a lot over the years and places like this have become more civilized and productive... usually.

    After not bothering with forums for half a decade I can now honestly say that they are now doing people some good. Arrogant, demeaning attitudes have toned down a lot. This is a good thing. Learning this stuff will do a person no good if they are also learning to act like a condescending, arrogant know-it-all
    jerk at the same time.

    What we do not have is a comprehensive list of what works and what does not. We need a bug list, a cheat-sheet that spans back over 15 years of people's experience with OpenGL, the new and the old. All updated, current and with nearly bug-free solutions because it's all of our combined experience with these various API changes and additions over the years.

    We have to do this ourselves, if I were to share some known bugs and pitfalls for beginners that none of them would likely find written anywhere unless they already knew what to look for, then it would be something the following.

    It would start a "benefits and bugs" wiki page that looks something like the following.

    //-================================================== ================
    Section-> (Fixed-function tied to GLSL)
    //------------------------------------------------------------------------------------------------------------------------
    PRO's: Very easy to use. A beginner could write and configure animation and lighting shader's very easily.
    //------------------------------------------------------------------------------------------------------------------------
    CON Not yet possible on mobile devices!)
    //------------------------------------------------------------------------------------------------------------------------
    CON: Most source code for this style was written when only a few driver models were automatically performing casting.
    There is a lot of very interesting source-code from that era, but even to this day, all of those horrible casting errors are still tripping
    up a lot of the new player's in the GPU arena. Driver's on mobile devices can't handle that much crap being thrown at them.
    //------------------------------------------------------------------------------------------------------------------------
    PRO: The Dynamic Duo are champs at fixing these problems with very little overhead.
    //------------------------------------------------------------------------------------------------------------------------
    Specific Bug listing A_1: gl_frontmaterial.shininess will not yield consistent results across many GPU's. Apparently, different manufactures are using a different procedures behind the scenes for this one. It's the only one I've found to be unreliable for cross-hardware/platform of all the common ones.
    //------------------------------------------------------------------------------------------------------------------------
    CON: Any time that a fixed-function material or lighting variable is used in GLSL: All possible fixed function material and lighting parameters available to GLSL will be added to the compiled shader even if they are not all being used. This is not as bad as it sounds, this method was working reasonably fast enough back in the Radeon9800/nVidia FX days so it's not going to slow down something made in the last few years. It's not practical for mobile devices yet but will not trip up a modern machine in the least. Not so far as most people go in their first several years. There are bigger fish to fry.
    //------------------------------------------------------------------------------------------------------------------------
    PRO: Learning to pass in your own Uniform variables is an easy enough optimization to consider once you've finally gotten your feet wet and you are not feeling so overwhelmed.

    //-================================================== ================================================== =============

    If the manufacturers will not give us a modern , up-to-date, fully backwards compatible bug repository then we will have to do it ourselves.

    Once a format for a wiki like this is decided upon, these bits of accumulated 'wisdom' can be posted to a wiki so people browsing the free repositories are not constantly stepping in poop.

    Just think back to when you had various successes and problems with all the different methods over the years. Give the good and the bad, how did using a feature make your life easier as a beginner? How did you overcome the pitfalls that you ran into? Things like this built into a wiki will make OpenGL a force that will knock people's socks off, but only if it includes everything OpenGL from beginning to end, 15 years of backwards compatibility that should become rock-solid stable and easy to learn.

    If I see any of it, I'll cut and paste it to a file that will eventually turn into a posting that can be attached to all the links of legacy open source code. Now that stuff won't be broken anymore. People will have instructions on how to fix it all when they use it.

    All those older pages should not be thrown away, they could be made productive and useful again, with little effort on our parts.
    //-----------------------------------------------------------------------------------------------------------------------------------------------
    Tip: For a lot of GPU's, even today, 1 and 1.0 are not the same thing! Don't rely on the driver to fix that for you. Certainly don't expect the shader to always work if you ignore this because it happens to work on your computer.
    Last edited by marcClintDion; 07-05-2013 at 05:41 AM. Reason: grammatical corrections/ proof-reading

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