How to speed up scene?

Transporter · Post by **Transporter** » Wed Oct 16, 2013 8:32 pm

Hi,

I have a big problem. I like to render 6 windows on 6 displays fullscreen (two graphic cards). I get 4 fps on each screen. The GPUs are used about 6%, one core of the 12 CPU cores is at 100% the rest is between 1% and 3%. It looks like the render loop is the bottle neck. I'm slightly shocked about the result. Any ideas how to solve this issue?

Thx,
Transporter

AlexeyKnyshev · Post by **AlexeyKnyshev** » Wed Oct 16, 2013 10:15 pm

It must be one process? Maybe you can start more then one instance of app? Or use multithreading?

tod · Post by **tod** » Thu Oct 17, 2013 8:09 am

I think there was some discussion of the forums about multi-monitor support and issues with it.

Transporter · Post by **Transporter** » Thu Oct 17, 2013 8:48 am

Of course I use multithreading, but this doesn't solve the problem. Ogre use multithreading only for resource loading, not for calculations.

I can't use Ogre on more than two displays at once. Maybe I have to switch the graphic engine.

Zonder · Post by **Zonder** » Thu Oct 17, 2013 9:16 am

Assaf has done this I believe (might be getting people mixed up) but try searching his posts

syedhs · Post by **syedhs** » Thu Oct 17, 2013 10:28 am

I get to render 6 monitors, but it uses two computers (two graphic cards each) as to ensure even the most complex scene can retain at least 60hz.

jessome · Post by **jessome** » Thu Oct 17, 2013 1:32 pm

If it's a panorama effect you're going for, you could use one large virtual window that spans multiple monitors.

I know, at one point in time, you could configure NVidia drivers to present several monitors as one logical display. ( i.e: 2x 1080p would equal 1x 3840 x 1080 display )

I think the issue is that with 6 screens ... if they're all culling and shadow mapping that's 6 viewports x # cameras per viewport. I know for me, that would be ~30 renders of the scene. That's 30 cullings, 30 render queue processings, etc. You might be able to re-use some of that work with a compositor, maybe?

Post by **Kojack** » Thu Oct 17, 2013 3:53 pm

If it's 6 monitors using 2 cards, how does it perform with 3 monitors on 1 card in comparison? Having to share all the resources between two cards may be causing problems.
(Not a fix, just trying to narrow down the cause)

Transporter · Post by **Transporter** » Thu Oct 17, 2013 9:06 pm

Kojack wrote:If it's 6 monitors using 2 cards, how does it perform with 3 monitors on 1 card in comparison? Having to share all the resources between two cards may be causing problems.
(Not a fix, just trying to narrow down the cause)

One window in window mode spread over all 6 displays (extended desktop) results is 22 fps. I'll try to setup two program instances (one for each card) tomorrow. I measured up to 60 fps if I cover two displays on one card with a window. Later, I like to setup 3 instances and 6 instances for tests about the performence.

Post by **Kojack** » Sat Oct 19, 2013 10:46 am

One thing that may be possible (just a theory of mine, not tested) is using a geometry shader for scene duplication. If you are using the 6 displays with 6 render targets, a geometry shader can make 6 duplicates of every triangle it receives and direct them onto different targets using 6 view matrices. So one render operation draws six different views. I've heard of this being done for rendering into all 6 sides of a cube map with one render call (such as for a dynamic cube map reflection of the scene).

Culling is harder in that case though, you could make the frustum wide enough for all 6 cameras or disable it somehow (if this is a wrap around view like a cave system).

What kind of scene is being shown, how do the monitors correspond to the scene, and what hardware is powering it all?

One of my ex students worked on this system:
[youtube]VGlxgKjg1ho[/youtube]
It's 12 IR touchscreen monitors (55 inch each) with a dual projector top display. It's using Unity. To run it, they needed 7 networked Xeon E5-2643 workstations with nvidia gtx 690 cards.
Trying to use Ogre (or any 3d engine) with a complex scene and just a single computer may be unrealistic. Pretty much every serious multi monitor (such as more than 4) system that I've seen (whether ogre or otherwise) uses multiple networked computers.

Zonder wrote:Assaf has done this I believe (might be getting people mixed up) but try searching his posts

Yep. Ogre with 6 monitors back in 2009. http://www.ogre3d.org/forums/viewtopic.php?f=11&t=48032

Transporter · Post by **Transporter** » Sun Oct 20, 2013 10:08 am

Kojack wrote:
Zonder wrote:Assaf has done this I believe (might be getting people mixed up) but try searching his posts
Yep. Ogre with 6 monitors back in 2009. http://www.ogre3d.org/forums/viewtopic.php?f=11&t=48032

Yes, but he has not drawn a part of a city - just a few figures. I'll try to get hardware instancing working. Does Ogre perform culling calculations if a scene node is set to invisible? I could cut the map into tiles with a head node on each tile. And I also know which tiles should be visible.

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