Author Topic: More info on the tearing problem  (Read 3210 times)

Afkpuz

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More info on the tearing problem
« on: February 16, 2009, 07:53:14 pm »
I know that ui2+alpha blending has that horrible tearing problem, and I've accepted that.  However, I'd like to understand it a little more than "It's just the NVIDIA driver".  What is causing this problem and why have I heard people say that it will probably not be fixed anytime (on NVIDIA's side) soon.  Thanks. 

colinjones

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Re: More info on the tearing problem
« Reply #1 on: February 16, 2009, 10:38:47 pm »
I think it is hasty simply to say "It's just the nVidia driver."

1) Firstly, it is clearly not a performance issue, as the exact same issue occurs on all chipsets, in the same way. This wouldn't be the case if it was simple performance.

2) When I run 3D games on the same system, from KDE, which are massively more taxing in terms of graphics, I can easily get perfectly smooth animation without any tearing at all.

3) The tear line (for me at least) is in exactly the same place on the screen all the time, about 10% from the top, or so.

4) The tear line appears to have a Z shape to it, actually back tracking, then continuing on its way across the screen a small distance further down the screen - others have reported this as well.

I cannot explain point 4 at all, it makes no sense whatsoever unless it is an artifact of the way my LCD scans out the image (this makes no sense either) so I'm just going to leave that point hanging and unexplained!

Point 3, to me, seems to suggest that the Vsync is working perfectly, and that the Vblank interval is more than sufficient for OpenGL to redraw the graphics before flipping the screen. The only explanation I can offer is that the graphics task is well within the card's capabilities, and the Vsync works, however it seems to be syncing it to the wrong time. ie the flip of the frame buffers is happening a set interval after screen re-refresh starts.

My take on all this is that it cannot be purely the driver due to point 2. So perhaps it is a combination of how the Orbiter code interacts with the driver in some way. One other point floating around in my mind is that I seem to recall that LMCE was switched from Ubuntu to Kubuntu and thus GNOME to KDE expressly because the KDE interface allowed graphics acceleration within the second + "virtual desktops" that LMCE runs within, and there was some kind of limitation on this within GNOME. I wondering if perhaps there is some issue in screen flipping when the Orbiter is animating to screens that are not the main KDE desktop screen...

I know this doesn't help fix the issue, just thought I would document my toughts on it, particularly the ones that seem to point away from a simple driver issue ... although if my last pondering is something to do with it, then perhaps it is a driver/KDE issue?

tschak909

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Re: More info on the tearing problem
« Reply #2 on: February 17, 2009, 12:25:24 am »
Basically, with nvidia's current code, combining opengl + composite + vsync seems to be a bit too much for the driver. It has nothing to do with the card. NVIDIA has been notified of the issue, but since nobody else uses the system in quite the same way that we do, I am not sure what they'll do about it.

-Thom

colinjones

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Re: More info on the tearing problem
« Reply #3 on: February 17, 2009, 02:10:54 am »
Basically, with nvidia's current code, combining opengl + composite + vsync seems to be a bit too much for the driver. It has nothing to do with the card. NVIDIA has been notified of the issue, but since nobody else uses the system in quite the same way that we do, I am not sure what they'll do about it.

-Thom


So basically, what you are saying, Thom, is that it is the compositing that pushes it over the edge? Or is it the driver-side implementation of OpenGL? I guess that the games I have tried don't have issues because they bypass OpenGL using SDL instead? Is there a bug report number for this with nVidia? Thanks!

krys

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Re: More info on the tearing problem
« Reply #4 on: February 17, 2009, 05:59:43 am »
does anyone use UI2 w+alpha? Do you just live with the tearing, or are have most people just resorted to UI2 regular? As nice is the +alpha is, I just cant stand the tearing. I have tried the wiki and it didnt help much, maybe bc I use PCI video cards.

colinjones

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Re: More info on the tearing problem
« Reply #5 on: February 17, 2009, 06:40:49 am »
I have seen some people say they have it working and without tearing, but I cannot see how this could possibly be given that everybody else's experience is identical with tearing!

totallymaxed

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Re: More info on the tearing problem
« Reply #6 on: February 17, 2009, 09:52:34 am »
does anyone use UI2 w+alpha? Do you just live with the tearing, or are have most people just resorted to UI2 regular? As nice is the +alpha is, I just cant stand the tearing. I have tried the wiki and it didnt help much, maybe bc I use PCI video cards.

We never use UI2 + Alphablending because of the tearing primarily but also because we have had consistent feedback from customers that they find it visually confusing in everyday use.

All the best

Andrew
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seth

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Re: More info on the tearing problem
« Reply #7 on: February 17, 2009, 02:01:46 pm »
 :)
I was using UI2+alpha for my living room MD. I did this because when I would use UI2-masked, the on-screen menu response was sluggish at best. I am not sure why this was happening to me, as it is an NVIDIA 7200GS card, but it was also happening to me on my man cave MD, which had a Nvidia 6200 card in it. I just dealt with the "Z" in the top of the screen.

However after seeing the post about getting better picture quality from PVR150 tuner cards - http://wiki.linuxmce.org/index.php/Pvr-150_picture_quality_guide and disabling de-interlacing, and enabling opengl from the wiki entry, my UI2-masked is smooth as silk.

I intend on testing this now with UI2-alpha, to see if it helps resolve the issue. If it does, then I just need to find a way to have the mythtv settings stick on a router reload, and then everything will be perfect.

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Seth
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Afkpuz

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Re: More info on the tearing problem
« Reply #8 on: February 17, 2009, 06:48:53 pm »
I've also noticed that UI2+alpha is more responsive and clears out very quickly once I've pressed a button.  In UI2+masking, calling up the gyro menu sometimes begins slowly and leaves black boxes.  I've just learned to live with it, but alpha blending eliminates that for me.

totallymaxed

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Re: More info on the tearing problem
« Reply #9 on: February 17, 2009, 07:22:29 pm »
I've also noticed that UI2+alpha is more responsive and clears out very quickly once I've pressed a button.  In UI2+masking, calling up the gyro menu sometimes begins slowly and leaves black boxes.  I've just learned to live with it, but alpha blending eliminates that for me.

Hmmm... dont see that here and we never use UI2 + Alpha.

Andrew
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seth

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Re: More info on the tearing problem
« Reply #10 on: February 17, 2009, 07:24:21 pm »
I've also noticed that UI2+alpha is more responsive and clears out very quickly once I've pressed a button.  In UI2+masking, calling up the gyro menu sometimes begins slowly and leaves black boxes.  I've just learned to live with it, but alpha blending eliminates that for me.

well that is almost exactly what I was experiencing. Using the steps from the wiki, specifically:

Disable De-Interlacing
Change method to libmpeg2
Enable OpenGL

Fixed that issue immediately. My UI2-masked is ultra smooth and responsive now.
Just have to figure out how to get the changes to stick on a router reload. But go ahead and try it. Just the first parts. I have not modified the recorded tv parts of it, just the playback. Makes it super nice.

Just give it a try  ;)

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Seth
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krys

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Re: More info on the tearing problem
« Reply #11 on: February 17, 2009, 07:50:57 pm »
I've also noticed that UI2+alpha is more responsive and clears out very quickly once I've pressed a button.  In UI2+masking, calling up the gyro menu sometimes begins slowly and leaves black boxes.  I've just learned to live with it, but alpha blending eliminates that for me.

Mine does this also, especially in MythTV, sometimes there is a 5-10 delay when calling on the menu, and black boxes intermittently I believe after you make your selection.

totallymaxed

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Re: More info on the tearing problem
« Reply #12 on: February 17, 2009, 08:55:06 pm »
I've also noticed that UI2+alpha is more responsive and clears out very quickly once I've pressed a button.  In UI2+masking, calling up the gyro menu sometimes begins slowly and leaves black boxes.  I've just learned to live with it, but alpha blending eliminates that for me.

Mine does this also, especially in MythTV, sometimes there is a 5-10 delay when calling on the menu, and black boxes intermittently I believe after you make your selection.

We never use Myth...maybe its some kind Myth specific issue... Do you see these artifacts outside Myth? ie just with the pss & UI2 menu bar on screen?

All the best

Andrew
Andy Herron,
Convergent Home Technologies Ltd

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seth

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Re: More info on the tearing problem
« Reply #13 on: February 17, 2009, 08:57:57 pm »
I only see it with mythtv. Playing back videos, or mythtv recordings from the video menu are usually liquid flawless.
However, by disabling De-Interlacing, changing the preferred method from "standard" to "libmpeg2", and enabling opengl the issue goes away instantly, at least until you reload the router.

Regards,

Seth
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colinjones

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Re: More info on the tearing problem
« Reply #14 on: February 17, 2009, 08:59:26 pm »
We don't use Myth (me, Andrew) so its looking like it maybe a Myth issue....