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OpenGL Advantage to OpenGL

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I saw that everyone here (that programs in 3d)seems to prefer OpenGL over Direct3D. Why is this? What exactly are the advantages to OpenGL? "Remember, I'm the monkey, and you're the cheese grater. So no messing around." -Grand Theft Auto, London

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That was just one poll and other polls have existed before. I think that most people here are using D3D, this is based from previous polls and that from my observations, a lot more of the questions asked in the various programming forums are D3D-specific. Also, a lot of people here are relatively new to computer graphics and nearly everyone starts on 2D graphics before they advance to 3D graphics, most tutorials use DDraw for the 2D graphics. Once one is familiar with DirectX and COM, learning something from the same family of APIs will generally be more appealing than learning a different standard.

I prefer OpenGL over D3D mainly because of idealistic values and a preference of coding style. I don''t particularly like the Hungarian coding style that goes along with COM and Windows programming and when I learned OpenGL (~2 years ago), it was clearly a superior API in terms of design and usability. Granted, D3D has made gigantic leaps in the past year, but I have not felt the need or pressure to change.

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I''ve never really had anything to do with DirectX until recently (I''m tentatively dipping my feet in the carnage that is DirectDraw at the moment), because I started straight into OpenGL and 3D programming (about 9-10 months ago).

OpenGL seems to have a much cleaner style to it than D3D, and I have certainly found it easier and more intuitive to learn. You also have the portability issue (with Linux becoming a bit of a force now), and OpenGL makes it easier to develop for multiple platforms.

A more immediate/recent advantage is the T&L accelerator support that OpenGL has (or does D3D use this too??).

Another bonus is that OpenGL doesn''t change spec every 23 seconds

I guess I''m just lazy, but I too do not feel inclined to learn D3D, and am quite happy with what can be done with OpenGL. Personal preference, I guess

-------------
squirrels are a remarkable source of protein...

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An obvious big advantage for OpenGL is that it is cross-platform, whereas D3D is Windows-only. Most people also feel that OpenGL is just a more elegantly designed API. The amount of setup code you need to write to get a simple polygon on screen has historically been much less under OpenGL than D3D, as D3D has, in the past, forced the programmer to handle every little detail of initialization, texture management, etc. In the early days of 3D hardware acceleration on PCs, this type of control is what game developers asked for, and Microsoft gave it to them.

Now, with so many different cards that implement so many different feature sets, it makes more sense to handle the details within the API driver (as the driver writers would, in theory, know best how to handle certain features for the card being used). OpenGL works well under this system, as it has always been a bit higher level than D3D, handling many details within the driver. To its credit, Microsoft has recognized this as a bit of a drawback to D3D and the past few versions have added functionality and utility libraries (like D3DX) to take away much of the common drudge work that used to be associated with D3D. Most people, myself included, no longer feel that D3D is a "horribly broken" (to invoke the words of John Carmack on this issue) API. However, many of the people who think it WAS a horrible broken API have so much experience with OpenGL at this point that there''s little reason for them to switch over.

Also, programming for OpenGL is not without its drawbacks.
For one, OpenGL and DirectDraw generally do not mix, and OpenGL''s framebuffer operations are amazing slow on many drivers. Also, Microsoft''s bindings for OpenGL on Windows -- wgl -- are horribly out of date (eg. multimon support? Heh) and its unlikely they will do much to fix the situation.

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The big advantage of OpenGL is that source codes of popular games are available like quake, doom,,,. People can get idea how popular games are doing. Direct3D does not have popular open souce games.

OpenGL is taught in many universaties. Lots of "brains" support OpenGL. This is why innovative work usually uses OpenGL, while Direct3D just uses results of OpenGL.

Kate

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Well the reason more people ask questions about D3D is ''cause it''s a damned sight harder than OpenGL, that''s not a representative statistic!

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Having read comments before on this board about GL/D3D, I decided to do something some might say is stupid, but I took the plunge and decided to try and learn a bit of both.

I can say, without doubt, I have come further with OpenGL than D3D, not because D3D is crap, it is a bit tough, and I agree with KeithV, thats probably why a lot of questions are asked about it.
I do feel that OpenGL has a much more clean and elegant design to it, and hence produces cleaner code (IMO, although any API can be misused to produce horrible source).
Although, OpenGL has been around for a long time now, and has had much time to develop/standardise, so that is to it''s advantage, D3D has made great leaps recently, and is not (anymore) a borribly broken API, and it seems more & more games are coming out with support for it.
I will continue in my conquest to learn both API''s, I hope it will stand me in good stead in the future. Also, I hope MS don''t re-vamp the frikkin'' thing before I''m done learning it.

All that aside, I do prefer GL.

Just my little addition to the on-going debate, take it as you will....

-Mezz

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I''m glad that for once someone hasn''t brought up silly things like "Carmack uses GL, so why shouldn''t everyone else in the whole world??? After all, he IS God!". I''ll just go ahead and add my two cents now.

First of all, I consider myself a very good graphics programmer, and I have done games in both D3D and OpenGL. In fact, I''m right now making a game that is both. Anyway, the thing that I''ve found is that they are two different API''s. Definitely different. Until you''re done setting them up. At that point, it just becomes a matter of function calls. Basically, the initialization where you tie it to your windows, you load some textures, and have a hell of a lot of fun is hecka different, but at least with D3D 7.0, we see not even a little difference from then on. Another nice thing that has happened to bring the two together is D3DX. I just discovered it a few months ago, and boy is it nice! Basically, your 20 line initialization from OpenGL becomes 5 in D3D, and they even made the calls more similar to draw! Personally, I am a D3D advocate, simply because I feel some taint on OpenGL that just doesn''t feel right. I think it''s the coding style, where everything is shrouded in mystery (everything being what''s actually happening down below the surface), as opposed to D3D giving you more control (and therefore more responsibility).

In addition, I think that at this point in time, most previously valid arguments have gone away. The fact that OpenGL is platform independent makes absolutely no difference for game companies. They still have to make a separate version of the game NO MATTER WHAT if they want it to work across the platform bounds. There are so many friggin API calls that require the programmer to know what OS is being used that the entire structure is often different. Also, there are no features in OpenGL that are not supported in D3D, though there are a few extra in D3D that make general coding nice. Nothing to write home about, but coding becomes easier as you find them. As for that "John Carmack is God, so if I use OpenGL, I must be a demi-god" argument, all I can say is get a life! He is one person who has been working on this type of stuff since before D3D was born, so OF COURSE HE''S GOING TO USE WHAT HE KNOWS!!! I also saw something about how some games that use OpenGL are open source, so you can look at the code. If you can seriously spend more than two minutes looking at their actual rendering routines, you probably have no idea what''s goin on. The three lines of code that are the rendering block can be just as easily converted to D3D. There is an entire game behind it that is really doing the graphics.

Back to the topic, I don''t see any advantages to OpenGL anymore, unless that''s all you know. If you don''t have time to learn D3D, by all means stay with GL, since it''ll probably be around for a few more years. If you do have time to learn D3D, though, I would recommend jumping on that bandwagon. It is developing in new directions, and with DX7, has made the leap past the single power that once was OpenGL.

Pythius

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Pythius, I think you''re wrong saying that it''s no longer significant that OpenGL is cross platform. In a world of unlimited timelines and unlimited budget it may be. However, I live in the real world. Quite frankly, If I develop something in Direct3D and want to run it on a Unix variant or, heaven forfend, a Macintosh. I''m going to have to port the graphics subsystem over to the new platform. Maybe I''ll have to port other parts of the application as well, but the less I have to port, the tighter my timeline is going to be. Additionally, if I port to a Unix variant, most likely the graphics subsystem is going to be in OpenGL anyway. So why waste the time programming with two different APIs when one of the APIs will run on both platforms? When I tell management that it''s going to be an additionaly 20 man-months for a DX version and a GL version, they''re going to say do only GL. And if I say that alternately we can modularlize out the graphics API calls, and get a graphics subsystem that isn''t optimized for either DX or GL, for an overall loss of quality, they''re going to say that quality matters so go GL. I''ve got nothing against DX for windows only apps, but cross-platform really does matter.

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Guest Anonymous Poster
Latest harware support of OpenGL is very impressive:

OpenGL hardware bump mapping is now supported by more cards than Direct3D: Geforce and ATI Rage128/Pro all support OpenGL hardware bump mapping, while Direct3D bump mapping does not work on these main stream boards.

Only Matrix400 supports Direct3D bump mapping, Direct3D bump mapping demo freezes with other video cards.

Virtual texturing: texture compression is now available by 3DLab.

Latest harware support of OpenGL is very nice.

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      The matrix that result from the multiplication of R and T (in that particular order) is send to my vertex shader as `r_Grid'.
      // spherify vec3 V = normalize((r_Grid * vec4(r_Vertex, 1.0)).xyz); gl_Position = r_ModelViewProjection * vec4(V, 1.0); The `r_ModelViewProjection' matrix is generated on the CPU in this manner.
      // No the most efficient way, but it works. glm::dmat4 Camera::getMatrix() { // Create the view matrix // Roll, Yaw and Pitch are all quaternions. glm::dmat4 View = glm::toMat4(Roll) * glm::toMat4(Pitch) * glm::toMat4(Yaw); // The model matrix is generated by translating in the oposite direction of the camera. glm::dmat4 Model = glm::translate(glm::dmat4(1.0), -Position); // Projection = glm::perspective(fovY, aspect, zNear, zFar); // zNear = 0.1, zFar = 1.0995116e12 return Projection * View * Model; } I managed to get rid of z-fighting by using a technique called Logarithmic Depth Buffer described in this article; it works amazingly well, no z-fighting at all, at least not visible.
      Each frame i'm rendering each node by sending the generated matrices this way.
      // set the r_ModelViewProjection uniform // Sneak in the mRadiusMatrix which is a matrix that contains the radius of my planet. Shader::setUniform(0, Camera::getInstance()->getMatrix() * mRadiusMatrix); // set the r_Grid matrix uniform i created earlier. Shader::setUniform(1, r_Grid); grid->render(); My planet's radius is around 6400000.0 units, absurdly large, but that's what i really want to achieve;
      Everything works well, the node's split and merge as you'd expect, however whenever i get close to the surface
      of the planet the rounding errors start to kick in giving me that lovely stairs effect.
      I've read that if i could render each grid relative to the camera i could get better precision on the surface, effectively
      getting rid of those rounding errors.
       
      My question is how can i achieve this relative to camera rendering in my scenario here?
      I know that i have to do most of the work on the CPU with double, and that's exactly what i'm doing.
      I only use double on the CPU side where i also do most of the matrix multiplications.
      As you can see from my vertex shader i only do the usual r_ModelViewProjection * (some vertex coords).
       
      Thank you for your suggestions!
       
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