OpenGL "Fuzz" Effect

Has anyone else noticed that whenever you use an OpenGL mode or other hardware acceleration mode, if you look closly at the screen you can see all this fuzzing all around. Kind of like blotches of static. I've seen this on tons of systems.

Anyone know what causes this and if anyone else notices it also?

Heh, I thought the thread would be about spectre fuzz emulation like there is in EDGE.

Can't say I have ever noticed the issue you speak about on my computers.

Nope. Can you post a screenshot?

Scet said:

Nope. Can you post a screenshot?

Can't post a screenshot, it only shows on real hardware. Can't take a picture either.

What you can do is go into any OpenGL hardware accelerated mode and look closely at the screen and you should see fuzzing like static.

It could be interference, but I am not really sure.

GhostlyDeath said:

Can't post a screenshot, it only shows on real hardware.

So the problem is with your monitor?

GhostlyDeath said:

Can't take a picture either.

Okay I'm not quite sure what you mean.

I don't recognize what you're describing, my best assumption is your eyes are too close to the monitor.

On a related note, I think this has to do with how my monitor can generate images, but if I stand in front of a wall and strafe to one side the texture starts to get chopped up and I get an image like this...



...drawn on the wall. I tried taking a screenshot of it at first but of course discovered that it's not Doom doing that as much as it is my monitor.

for reference, that's just screen tearing. It happens when the video hardware starts rendering another frame while the current frame is in the middle of being displayed, and happens because the frame rendering rate exceeds that of the monitor's refresh period.

Most games, including most source ports, have an option to wait for the frame to finish displaying before rendering the next one. It's usually called Vertical Sync, or VSync.

I had an SiS-based motherboard that had onboard graphics with fake OpenGL. GL programs would look "dithered" while being run. Come to think of it, it probably was dithering...

My laptop also has a fuzz effect (which looks similar to the "spread" noise filter in GIMP), but only when upscaling 640x480 modes to the LCD's native resolution.

If you use an analog VGA output with many cheap LCD monitors, you'll get visible noise on certain colors/color combinations/transitions. This is because of poor ADC conversion inside the monitors (they have to sample the analog signal, store it in a digital frame buffer, and reconvert it to analog to drive the pixels).

Most monitors only have 6-bit Flash ADCs per color channel, while SVGA has typically 8 bits per color, for 24-bit and 32-bit displays. So by doing this poor sampling you get so-called "quantization noise".

This problem doesn't exist on purely analog CRT monitors that can be driven directly by the video card, only on LCDs that need to completely buffer an image before displaying it (and often they need to buffer several images in order to compensate for using chapo TN panels instead of true TFT).

So does this only happen in Doom ports or is it any 3D accelerated program?

It may be your card overheating. I've heard of people getting random noise in textures or even the frame buffer when the card overheats.

CODOR said:
I had an SiS-based motherboard that had onboard graphics with fake OpenGL. GL programs would look "dithered" while being run. Come to think of it, it probably was dithering...

I saw something like that in Unreal, using an SiS card, but not anywhere else. It was something much more obvious than what GhostlyDeath is describing, though.

The fact that it only shows up in one particular game makes me think that it actually occurs at a particular resolution/refresh rate. If the monitor can't really keep up with either, CRTs will first whine then go berserk, while LCDs will start to glitch and then lose signal altogether.

Try switching ZDoom's resolution to something lower, and sync it to your monitor.

Alternatively, if you're using a LCD/TFT try manually adjusting the "pixel clock" in the monitors' most advanced settings.

Maes said:

If you use an analog VGA output with many cheap LCD monitors, you'll get visible noise on certain colors/color combinations/transitions. This is because of poor ADC conversion inside the monitors (they have to sample the analog signal, store it in a digital frame buffer, and reconvert it to analog to drive the pixels).

Most monitors only have 6-bit Flash ADCs per color channel, while SVGA has typically 8 bits per color, for 24-bit and 32-bit displays. So by doing this poor sampling you get so-called "quantization noise".

This problem doesn't exist on purely analog CRT monitors that can be driven directly by the video card, only on LCDs that need to completely buffer an image before displaying it (and often they need to buffer several images in order to compensate for using chapo TN panels instead of true TFT).

I yanked out by old Sony Trinitron E200 and it does not do this at all. The display is nice but it got water damaged sometime back so it's not perfect, there's water stains behind the front glass panel, who knows how to get rid of that. But the display is so clear. Anyway, does not happen. Using a standard GUI you don't see anything, it's really only noticeable when using OpenGL.

If only CRTs didn't cause blindness and headaches.

GhostlyDeath said:

If only CRTs didn't cause blindness and headaches.

Only crappy ones should do that anyway. That being said, some people can't even use hi-end CRTs and I knew a person that actually got dizzy and vomited even with a 200 Hz display.

For your problem, you could try lowering the resolution or force the refresh rate in OpenGL games to be fixed and synced. This way, you'll have less bandwidth towards the monitor and perhaps -but not absolutely certainly- the crappy circuitry will cope better with it.

GhostlyDeath said:

If only CRTs didn't cause blindness and headaches.

Hahaha, that's hilarious!

Maes said:

That being said, some people can't even use hi-end CRTs and I knew a person that actually got dizzy and vomited even with a 200 Hz display.

The CRT monitor I have is high quality and it's very nice, but it stopped being high quality when it got water damaged by a globe.

There was a metal shelf above monitor that was railed and all, the shelf fell off and a snow globe smashed into the monitor. The monitor displayed a cool looking red sine wave in the front, which then turned green minutes later. Eventually the display came back missing colors and having a purplish tint. Now it has a slight purplish tint and water stains behind the front glass. Who knows how to fix that up.

GhostlyDeath said:

Eventually the display came back missing colors and having a purplish tint. Now it has a slight purplish tint and water stains behind the front glass. Who knows how to fix that up.

OK, that puzzled me. It has water stains behind the frontal glass of a CRT? :-S

That should be one solid piece of leaded glass, they're usually not multilayered like that (unless there was a thin coating that can be separated). The tint can probably be fixed by replacing some caps (I had a monitor that blew a couple of caps while working, and the tint shifted to green. A visit to a TV technician was enough to restore it, and actually make it even better than before).

I'd say take it to a TV tech: removing stuff mounted around a CRT is risky if you don't know what you're doing, and cleaning that shit up probably requires complete frame disassembly to access whatever overlay panel is in front of your CRT.