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ShawMishrak

OpenGL OpenGL and C vs C++

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I remember reading a thread a month back or so on this subject, but I cannot find it as the search function is not available. I have been using OpenGL inside C++ classes for a couple years now, but a question has been bothering me recently: Should I use C++ or C to write the graphics engine? I originally thought C++ classes were the way to go to keep everything together and pretty. However, I read an article about Doom3, and in it was an interview with Carmack in which he stated that the game was written in C++, with the exception of the graphics engine, which was written in C. This made me think; is C faster or better than C++ when it comes to OpenGL? If so, which parts should be written in C and which in C++? Should the whole graphics engine be written in C, or just the functions that interface directly with OpenGL? I''m just looking for any advice, since this question has been bothering me lately and I haven''t been able to find anything online beside that thread which I now cannot find.

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C is slightly faster than C++ because it doesn''t have virtual functions (with virtual functions, the program has to figure out which methods to call at run-time rather than compile-time). That''s probably why he used it. However, most compilers do enough optimization that the difference is negligible. It''s perfectly possible to create a great graphics engine in C++. Doom 3 isn''t the only game in the world with great graphics, you know.

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quote:
Original post by DC_Tsunami
C is slightly faster than C++ because it doesn''t have virtual functions...
You only get the overhead of virtual functions if you declare them as virtual!

And getting the same effect in C requires the exact same overhead.

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Possibly C just suits the style of engine iD/JC want to write.

Also .. Quake and Q2 were definitely written in C .. possibly Q3 (dunno, haven''t seen the code) .. in which case they may just be building on the (known good) technology they already have.

tbh, what everyone else says above: use what works for you

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as I side note, from what I read about Doom3 the only hold overs from Q3 to start with was stuff like loading code, audio code etc, the graphics engine was apprently gutted and started again from the beginning.

As for C vs C++ in the case of Doom3, its probably a case of JC just likes/knows how to use C more than C++ to get better results, so if you prefer to go with C++ over C then do so, basical at the end of the day its whatever works for you

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I personally think C is the way to go. C++ might be good for GUI''s and whatnot, but when it comes down to doing efficient graphics code, you want to make as few function calls as possible. You want to avoid setting the same things over again if they''ve already been set (textures, colors, etc). I find it difficult to impliment that well with classes since you basically want to sort and render things on a polygon (or strip or whatever) basis rather than on an "object" basis. When you try to do all that with C++, you might end up basically writing C code in a .cpp file, and I prefer direct access to data in structs and arrays over accessor methods any day. If you can optimize it with classes, more power to you, but I''m sticking to C when it comes to rendering.


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quote:
Original post by jitspoe
C++ might be good for GUI''s and whatnot, but when it comes down to doing efficient graphics code, you want to make as few function calls as possible. You want to avoid setting the same things over again if they''ve already been set (textures, colors, etc).

So group your data by texture, color, etc. Write a data manager that does this for you.

quote:

I find it difficult to impliment that well with classes since you basically want to sort and render things on a polygon (or strip or whatever) basis rather than on an "object" basis.

No offense, but your ineptness at a technique is not a valid argument against it.

Not that I''m advocating C++. This is a pointless argument/discussion/thread. Yeah, Doom3''s graphics engine is written in C. UT2003/Unreal Championship''s is written in C++. If you''re asking a question like this, your code is unlikely to be efficient or well-structured enough for it to make a difference.

So get back to work. Real work.

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personally i use c++ but more as ''a better c''(tm)

in the old days c used to be quicker cause the c compilers used to be better than there c++ counterparts (mainly cause c is a simpler language IIRC only 21 keywords), nowadays c++ compilers will produce code around the same speed a c compilers.

what language u choose is not gonna make any difference to the final speed of your game all speed is in made in the hands of the programmeur/s (usually by choosing the most efficent algorithms)

personally i feel sorely tempted when i read posts ''java is slow'' of rewriting my KEA game in java, the only thing stopping me is, i dont know java + are unwilling to spend a month learning it.



http://uk.geocities.com/sloppyturds/kea/kea.html
http://uk.geocities.com/sloppyturds/gotterdammerung.html

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Yes, there is a performance issue with C and C++. You should be coding everything in ASM.

More seriously though, as has already been stated, you can get the same speed from C++ as from C (C being a subset of C++, this is to be expected).

If you care about performance, do some profiling, and find where the slowest parts of your code are. Most likely there''ll be one or two inner loops which could be optimised, and nothing else will make any difference. If you''re concerned about the overhead of virtual functions, bear in mind that all functions have a calling overhead, and in speed-critical inner loops you''re not going to be calling functions anyway (unless they''re inlined).

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