[gpz]

nyc01, on 27 March 2013 - 08:43 PM, said:

If you are mainly running older games/sims that use DirectX 9 I'd stay away from AMD. I've never been able to get close to the image quality I'm getting with my Nvidia GPU's with the AMD 7970 I'm running in one machine with OpenRails or TS2013.

Just a note here: OpenRails also uses DirectX 9.

[Genma Saotome]

Walter, AFAIK, the Updater % is pure Open Rails game stuff, like brakes and calculating where the train is, and the Render % is preparing all of the data to send to the GPU plus interacting w/ the video driver. What's not measured by Open Rails is the time taken by the GPU itself to do its thing.

That said, there are other software that says they do measure what the GPU is doing and IF they're right about that you can see how busy the GPU is while OR is running. One such item is a Win 7 gadget that monitors the GPU. When I set the gadget to always display on top and put OR into windows mode I can see on my PC the Updater is ~30%, Render % is 90-100%, and the GPU is 45-71%. The GPU is an AMD 5800 series chipset. Between 9000 and 10,000 primitives (both kinds) were being processed. FPS ranged from a low of 22 to mid 40's. The GPU busy number was highest when the fps were highest and lowest when fps was low.

That data suggests to me is my CPU (i750 quad core) has all it can deal with in preparing data to send to the GPU -- probably because of the very high primitive count. But once it manages to stuff the buss and turn it over to the GPU, the GPU manages quite well so long as the fps are below 50. Note that my monitor is capable of displaying 60fps -- no more. Ditto for most monitors.

So in my case I need a faster/more capable CPU to process the render data faster. But once I do that I might start to hit the ceiling of what the GPU can do. IOW if I overclock my PC I should upgrade my GPU. OTOH It makes little sense to upgrade my GPU on it's own... it won't make any difference on the route I just tested... and on others I couldn't care less if fps are > 60 because my monitor won't show me those frames anyway.

[Genma Saotome]

nyc01, on 28 March 2013 - 10:09 AM, said:

So if the Win 7 gadget is accurate (which it's well known that even GPU-Z doesn't give a good representation of GPU utilization) what exactly is keeping the GPU busy besides maybe very high resolution at high AA settings?

Are there some advanced lighting and shadows calculations being done on the GPU? Obviously it can't use GPU compute at this time so what would be so demanding on the video card in OpenRails?

Per the data available, the GPU isn't being over-burdened, the CPU is.

IF the gadget is accurate ( a speculative assumption) the data in my test indicates my GPU is not being maxed out when the fps is under 50. And the lower the fps, the less work the GPU is doing. My conclusion is the route being tested makes the whole PC CPU bound (that's what the Render % is suggesting, supported by the high primitive count). As the primitive count went up the fps went down.

And if the route indeed makes the PC CPU bound than there should be some relationship between an increase in primitives and a decrease in both fps and GPU loading... and that is what I observed.


At any rate, don't overlook the fact that when the fps hit 60 my monitor becomes the bottleneck: Everything else may be flying along at 160fps... but I only get to see 60 of them no matter how much money I might have spent on the rest.

Last, if the gadget is totally bogus then about all I can do is quote Emily Litalle: Nevermind. :)

[cjakeman]

Hi nyc01,

nyc01, on 27 March 2013 - 08:43 PM, said:

How much does image quality matter to you?

Here are some screen shots (post #29) taken with a six core i7 and a GTX 680 -

Thanks for such a detailed reply.

I seem to have kicked of a busy thread mostly about achieving high frame rates, but you have tried to answer the question I was asking - about everything but frame rates or, in your words, image quality.

You mention "super-sampling anti-aliasing enabled" which sounds good and must be a feature of the graphics card independent of OR.

I wonder whether there are other features which do depend on OR but are ignored on lower spec graphics cards.

I have attached a cropped image from the start of Settle and Carlisle:Short Passenger Run saved with a minimum of compression. Are you able to post a similar image from one of your high-end cards as a comparison?

[Lindsayts]

Just in case its not to clear "Anti Aliasing" is a technique used to smooth the the edges of a displayed object caused by the display device having a finite sized display elements. You can usually see it in action (or not) on distant telegraph poles, with elements of the object blinking on and off as the scene moves. These days its mostly a function of the video card. From experience theres quite a few "gotchas". I have found in OR it works on some objects and not on others.

One of the problems with a train sim is the huge amount of data that must be sent to the video card to display a scene. A single triangle consists of 3 vertex's each consisting of 3 32 bit numbers, ie one triangle takes 36 bytes of data to describe its shape. A locomotive of 100,000 triangles could take anywhere between 400k to 1 Mbyte to describe its shape. A single terrain tile takes around 600 Kbytes of shape data and 9 of these are displayed. Its not hard to see that the amount of data that it takes to describe a single frame can reach __VERY__ large numbers and all this has to be sent to the video card in only a few milliseconds between frames. I actually question if an SLI system will actually be an improvement in a train sim in a high object count route as as far as I can all data including textures has to be sent individually to BOTH cards and the CPU's appear to be having some problems sending it to a single card.

It appears an SLI system assumes the GPU is the bottleneck, I believe this is not the case in a trainsim on a high object count and high detail route.

Note: The above Data bandwidth problem is a known issue in GPU design and considerable efforts have and are being made by both Nvidia and AMD to find an effective solution to the problem.

Lindsay

[cjakeman]

nyc01, on 28 March 2013 - 11:53 AM, said:

Is that one of default routes in MSTS?

Yes, that's right. Your locos look very good but I was hoping for a point of comparison.