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4mad3u5

OpenGL
Opengl design

23 posts in this topic

In the opengl wiki it say: "Although it is possible for the API to be implemented entirely in software, it is designed to be implemented mostly or entirely in hardware." Can anyone expand on that? How would it be  implemented entirely in software, and how is that different than on hardware? 

 

wiki design:

http://en.wikipedia.org/wiki/OpenGL

Edited by 4mad3u5
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You can definitely play games like Quake 1 - 3 on a software only renderer. With things like AVX2, DDR4 and cpus with 8+ cores, the performance disparity between software rendering and "hardware" rendering decreases significantly.

Edited by Chris_F
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Maybe I should have said "play a game with 16 year old graphics at less than 1 fps" instead then, eh?

 

The point is: "Quake" wasn't meant to be taken literally, and it's a shame that it was because doing so totally detracts from the point being made here, which is that the common software implementations are slower than is practical for use.

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I was expecting someone to point out that both "hardware rendering" and "software rendering" are run on hardware. It's just that first one runs on the GPU and second one on the CPU. That's all there is to it.

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If your 3D experience is limited only to games with fast frame rates and soft-realtime requirements, then it might be reasonable to only think about hardware implementations.  But if your 3D viewpoint includes offline processing, such as rendering that takes place in movies, print, other physical media, or scientific rendering, software rendering is a pretty good thing.

 

 

Sorry I am new to this, what are soft-realtime requirements? And I think hardware implementations are processes that go through the gpu? I'm not quit sure what software rendering is, Processes that are implemented through the cpu?

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I'm not quit sure what software rendering is

 

A software renderer is any render which is implemented in software instead of by specialized hardware, such as a GPU.

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I'm not quit sure what software rendering is, Processes that are implemented through the cpu?

 

Software rendering runs on the CPU, hardware rendering runs on the GPU.

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How many flops are you guys getting? You are doing floating point ops in software and hardware?
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 If you want to do anything serious, forget about software right now.

This is very true, and I'm sorry I was not able to take part in this discussion earlier, since I think it went in wrong direction.

 

Rendering time does matter! It matters a lot, so I have to disagree with most "facts" frob used to illustrate his opinion.

 

But if your 3D viewpoint includes offline processing, such as rendering that takes place in movies, print, other physical media, or scientific rendering, software rendering is a pretty good thing.

 

It is maybe good, but HW accelerated is better. With legacy OpenGL it was really necessary to implement algorithms on the CPU side in order to have ray tracing and similar stuff. But now it is not. And if we have several order of magnitude acceleration through GPU usage, I simply don't understand why anybody would defend slower solutions.

 

There are some cases when CPU can beat GPU in rendering. That is a case when cache coherence is very weak, when different technologies compete for the resources and communicate through high number of small buffers that have to be synchronized. In most cases, beating GPUs like GK110 (with 2880 cores, 6x64-bit memory controllers, GDDR5 memory) in graphics stuff (where parallelization can be massive) is almost impossible. And we are taking about orders of magnitude!

 

 

Think about the resolution we get out of modern graphics cards.

 

Monitors with DVI can get up to about 1920x1200 resolution. That's about 2 megapixels.  Most 4k screens get up to 8 megapixels. Compare it with photographers who complain about not being able to blow up their 24 megapixel images. In the physical film world, both 70mm and wide 110 are still popular when you are blowing things up to wall-size, either in print or in movies. The first is about 58 megapixel equivalent, the second about 72 megapixel equivalent. 

 

When you see an IMAX 3D movie, I can guarantee you they were not worried about how quickly their little video cards could max out on fill rate. They use an offline process that generates large high quality images very slowly.

What does the resolution matter? This is a very inappropriate example.

IF GPU can render a 2M scene in 16ms, 72M scene can be rendered in 576ms. That's only 0.6s.

Using CPU implementation (what we call "software") it would take almost a minute.

Of course, it depends on the underlaying hardware.

 

 

In the film industry, I bet it is not irrelevant if some post-production lasts several days or several months.

There are a lot GPU accelerated renderers for professional 3D applications, although they are using CUDA (probably because it was easier to port it to CUDA than to OpenGL, and because there is lack of precision control and relatively new tessellation and computation support in OpenGL).

 

 There are companies today that sell even faster software rendering middleware for running modern games with real-time speeds for systems with under-featured graphics cards that cannot run modern shaders .

Can you give some useful link? How can CPU be even near the speed of GPU and also do some other tasks (AI, game logic, resource handling, etc.). This is SF, or far slower than it should be to be useful. Be honest, who will buy 3D video cards if games can be played smoothly on the CPU only?

 

You can definitely play games like Quake 1 - 3 on a software only renderer. With things like AVX2, DDR4 and cpus with 8+ cores, the performance disparity between software rendering and "hardware" rendering decreases significantly.

I really doubt in it. Any useful link to support this claim?

Edited by Aks9
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I really doubt in it. Any useful link to support this claim?
Here is an overview of the Quake 2 software renderer:

 

http://fabiensanglard.net/quake2/quake2_software_renderer.php

 

IIRC, it was the main renderer people used when it came out, there weren't many people with hardware accelerated cards (we're talking of people running Quake 2 rendered with the first Pentium CPU, not 8 core number crunching monsters) All previous Id games also used software renderers (Quake 1, Doom, Wolfenstein 3D). I'm not sure if Quake 3 had one.

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I really doubt in it. Any useful link to support this claim?
Here is an overview of the Quake 2 software renderer:

 

http://fabiensanglard.net/quake2/quake2_software_renderer.php

 

IIRC, it was the main renderer people used when it came out, there weren't many people with hardware accelerated cards (we're talking of people running Quake 2 rendered with the first Pentium CPU, not 8 core number crunching monsters) All previous Id games also used software renderers (Quake 1, Doom, Wolfenstein 3D). I'm not sure if Quake 3 had one.

 

 

The Quake 2 software renderer was not a software implementation of OpenGL, which was what the OP was asking about.

 

At this stage I really really regret even mentioning the word "Quake" here as my doing so seems to have steered this thread down a completely irrelevant path.  What I meant was a Quake-like level of scene complexity, as in low-polycount, low-resolution textures, low screen resolution (maxing out at perhaps 640x480 or 800x600), no complex effects, etc.

 

And of course offline rendering still uses software, but again this is completely irrelevant.  We're gamedev.net so we're talking about realtime rendering in a game engine using consumer-level hardware, unless explicitly stated otherwise.

 

So taking these two together, that's the kind of scenario where a software OpenGL implementation will get you below 1fps even with the low level of scene complexity I mention.  Yes, even on a modern CPU.  Anybody want a citation?  OK, see for example this thread where the OP in it got 0.5fps owing to using an OpenGL feature that was supported by the driver but not in hardware.

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Except a good software renderer like WARP or LLVMpipe can run that kind of scene at more than playable FPS.

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At this stage I really really regret even mentioning the word "Quake" here as my doing so seems to have steered this thread down a completely irrelevant path.  What I meant was a Quake-like level of scene complexity, as in low-polycount, low-resolution textures, low screen resolution (maxing out at perhaps 640x480 or 800x600), no complex effects, etc.
 ...  
So taking these two together, that's the kind of scenario where a software OpenGL implementation will get you below 1fps even with the low level of scene complexity I mention.  Yes, even on a modern CPU.  Anybody want a citation?  OK, see for example this thread where the OP in it got 0.5fps owing to using an OpenGL feature that was supported by the driver but not in hardware.

It all depends on what features you want.

 

I know you regret bringing up quake, but it is actually a good example. They released two versions, one using their custom rasterizer and another using the OpenGL rasterizer. IIRC they released the source for both. Just a hunch, but I'm fairly confident if you ran GLQuake with Mesa software drivers you'd probably still see a highly performant game on today's hardare.

 

The specific post you mentioned was fairly high polygons using a blending function. Neither of those fits the quake-style graphics which were low polygon and simple texturing.

 

Naturally if you are trying to run something complex in a software renderer, such as your collection of modern shaders or even a moderately complex blending function, then yes you are quickly going to get bogged down.

 

 

The first question was "what does this mean?" which I think was fully answered.

 

The second question was "is this possible?" which is a little more complex. It is certainly possible to make a fast 3D opengl game with a software renderer if you limit yourself to a subset of the features. It is also possible to make a 3D opengl game with a software renderer that takes hours per frame.

 

The OP was about OpenGL design. OpenGL is about rendering generally, and the design reflects that. Games represent a subset of what OpenGL does.

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Except a good software renderer like WARP or LLVMpipe can run that kind of scene at more than playable FPS.

Thanks for the examples. I was not aware that WARP even exists. It is really great, BUT it is a substitution in the cases when there is no GPU in the system, or drivers don't support 3D acceleration on such GPUs. As a substitution, it enables rendering, but it is at least an order of magnitude slower (which is excellent result) than there is a GPU. Usually it is almost two orders of magnitude. Anybody could easily experience that through 3DMark tests.

 

The first question was "what does this mean?" which I think was fully answered.

 

The second question was "is this possible?" which is a little more complex. It is certainly possible to make a fast 3D opengl game with a software renderer if you limit yourself to a subset of the features. It is also possible to make a 3D opengl game with a software renderer that takes hours per frame.

 

The OP was about OpenGL design. OpenGL is about rendering generally, and the design reflects that. Games represent a subset of what OpenGL does.

 

I completely agree that it is possible to do everything on the CPU side, but it is not a wise decision. OP has a very naive question, and I hope he had a better insight now. I'm glad that there are some efficient CPU based implementations, but they should be used only when any other alternative is impossible. Probably every low-end GPU can easily outperform the fastest commercial CPU, leaving it free to do other tasks.

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I completely agree that it is possible to do everything on the CPU side, but it is not a wise decision. OP has a very naive question, and I hope he had a better insight now. I'm glad that there are some efficient CPU based implementations, but they should be used only when any other alternative is impossible. Probably every low-end GPU can easily outperform the fastest commercial CPU, leaving it free to do other tasks.

 

Well there are cases, outside of the game development space, where software makes sense.  For example, the first line of the "invariance" section in your local friendly OpenGL specification warns you that OpenGL is not a pixel-exact specification.  So if you need pixel-exact results, you must look elsewhere.  Likewise the supported floating point precision limits may not meet some rendering requirements.

 

But these are outside of the game development space.  The general case is that neither is a perfect replacement for the other, so like any other tool sets, you pick the tools that match the job you want to do.

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