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Taxiline Flickering Issue

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Taxiline Flickering Issue

Postby Imran Anees » Sat Apr 16, 2016 11:33 am

This is an issue which is still unsolved. Even though if you'd set the ALS, Anti-aliasing on and Landmass, Transition effect to maximum, it still persists in some perspective angles. It'd be great if we are able to solve this issue, and set non-flickering taxilines without ALS, Anti-aliasing and max. effects. This would allow users with low-powered machines to enjoy flying without this problem. So, is this problem solved or is team trying to terminate the flickering.

P.S. I was able to terminate the issue, but I was asking if this issue could be terminated with the default FG Settings. (BTW, this issue could be solved with graphics card with great anti-aliasing support.) :D :D
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Re: Taxiline Flickering Issue

Postby Thorsten » Sat Apr 16, 2016 11:57 am

A small line feature seen from an arbitrary distance will flicker because the rasterizer doesn't always pick it up - that's not your standard z-fighting issue which can be addressed by z-displacement but a fundamental limit of fragment processsing. The only solution is, as you realized, anti-aliasing, so I suggest to crank up the number of multi-samples being done.

There's no way to conceptually solve this without multi-sampling.
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Re: Taxiline Flickering Issue

Postby jaxsin » Sat Apr 16, 2016 12:49 pm

Thorsten, does --texture-filtering effect this well? I am not sure what has more of a derogatory effect on the GPU, but one could mix and match if it did help. Thinking out loud...
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Re: Taxiline Flickering Issue

Postby Thorsten » Sat Apr 16, 2016 2:07 pm

The problem would be absent if the taxiline would be a texture, because then it could be mipmapped (sort of pre-computed antialiasing). But in actual fact the line is a vector structure (it's not painted on the runway mesh, it has its own mesh), so texture operations don't help you.
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Re: Taxiline Flickering Issue

Postby Imran Anees » Sun Apr 17, 2016 7:56 am

So will the team take step to terminate the issue by coming releases or is it never possible to solve it, cause it'd be a great improvement in the scenery.
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Re: Taxiline Flickering Issue

Postby Thorsten » Sun Apr 17, 2016 9:17 am

If we mean the same issue, the solution is to use multi-sampling. Which is, 'the team' already provides a solution, it's up to you to use it (or not).
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Re: Taxiline Flickering Issue

Postby Imran Anees » Sun Apr 17, 2016 9:44 am

Do you mean enabling Anti-aliasing and set to 4setting. I have already done that and although it may seem gone whn looking close at it. It actually isn't at a more posts ider angle of view, especially when users try take a shot from an interesting angle outside the aircraft, the flickering just makesit seem bad.

I have ALS, Anti-aliasing, Transition and Landmass settiilng to high, but I have the problem at an angle of view as I talked about earlier.

Other than that everything else is good. Cheers for that.
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Re: Taxiline Flickering Issue

Postby psadro_gm » Mon Apr 18, 2016 5:32 pm

I may be wrong, but the ALS fix works when the lines are near coplanar. The issue of taxi-lines 10s of cm above the pavement have been reported as well. These can bust your landing gear. I have a fix for this in the terragear toolchain, and will be available in a future scenery release.
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Re: Taxiline Flickering Issue

Postby Thorsten » Mon Apr 18, 2016 5:43 pm

The issue of taxi-lines 10s of cm above the pavement have been reported as well. These can bust your landing gear.


If the mesh is displaced, they don't flicker due to z-fighting. If the mesh is not displaced, the shader can do it, but that's visual only, the ground interaction code never learns of this - what happens on the GPU stays on the GPU...

Actually I have no real idea what the OP is trying to describe, I know just two types of flickering of the lines.
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Re: Taxiline Flickering Issue

Postby xxx-246 » Wed Sep 19, 2018 1:50 pm

... A bit more than one year and this problem celebrates it's 10. birthday (maybe it's older, the oldest post I found is over 8 years old regarding that issue).

For me, I can see the flickering (more or less intensive) with all renderer options. Anti Aliasing 4x or not, ALS, rembrandt, ..., doesn't matter.
Don't know which "solution" people are taking about. In my opinion, it's just a bug.

If the problem is, that the taxi lines aren't textures, why don't we change the taxilines to be textures instead of meshs ?
How are other simulations dealing with that task ?
I'll try to start playing with those taxi lines.
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Re: Taxiline Flickering Issue

Postby Thorsten » Wed Sep 19, 2018 2:32 pm

Works fine and flicker-free here (just needs the rendering quality high enough(, and does so for everyone else I know, so you're the first to report otherwise since the ALS fix was done. No birthdays as far as I am concerned.

If the problem is, that the taxi lines aren't textures, why don't we change the taxilines to be textures instead of meshs ?


It's OpenSource - please pursue whatever solution you like and if it's better than the current one, we'll be happy to include it (you'll discover things like resolution issues requiring gargantuan textures, the generic nature of FG runways making it difficult to add extra goodies,...) but all these can be overcome with some dedication I guess.
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Re: Taxiline Flickering Issue

Postby legoboyvdlp » Wed Sep 19, 2018 2:35 pm

xxx-246 wrote in Wed Sep 19, 2018 1:50 pm:
For me, I can see the flickering (more or less intensive) with all renderer options.


Is the transition shader enabled?
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Re: Taxiline Flickering Issue

Postby WoodSTokk » Wed Sep 19, 2018 8:58 pm

xxx-246 wrote in Wed Sep 19, 2018 1:50 pm:... A bit more than one year and this problem celebrates it's 10. birthday (maybe it's older, the oldest post I found is over 8 years old regarding that issue).

For me, I can see the flickering (more or less intensive) with all renderer options. Anti Aliasing 4x or not, ALS, rembrandt, ..., doesn't matter.
Don't know which "solution" people are taking about. In my opinion, it's just a bug.

If the problem is, that the taxi lines aren't textures, why don't we change the taxilines to be textures instead of meshs ?
How are other simulations dealing with that task ?
I'll try to start playing with those taxi lines.


Thats a problem of triangles in 3D space. The renderer paint triangles from far to near. The distance of an triangle is stored in the so called z-buffer.
If 2 or more triangles are on the exact same space, they have the exact same z-coordinate. Sometimes the first triangle will be rendered first and sometimes the other. In conjunction with the framerate, you will see a flickering, this is calles 'z-fighting'. The triangles fight for preference or priority.
To counter this phenomena, there are several ways.
Mostly the scenery developer rise the line meshes (ca. 10cm). With this approach the lines have a lower value in the z-buffer and will be rendered later.
But if you switch to a external view and look extremly flat over the ground, you notice that the lines are above the ground. Sometimes the line have a high that they go through the middle of the wheels. That looks odd.
Another problem is, that the line meshes are solid. I see it very often that the airplain jumps at taxiing if the nose wheel roll on and off the line.
I know from another OpenGL engines that they use priorities specialy for that matter.
All textures have a default priority of 0. Some textures (especialy alpha textures to overlay) have a higher priority.
So, if 2 or more textures have the same value in the z-buffer, the textures will be rendered in ascending order of the priority.

But i dont know if the second approach can implemented in FG.
All textures (mostly alpha) that are used to paint on pavement (lines, numbers, signs, etc...) should have a priority higher than 0.
The scenery developer dont need to rise the meshes of paintings.
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Re: Taxiline Flickering Issue

Postby Thorsten » Thu Sep 20, 2018 4:38 am

Mostly the scenery developer rise the line meshes (ca. 10cm).


Mostly they do not (because these lines are real geometry and wold be an obstacle for taxiing) - it would appear that rarely some lines are raised in the mesh (never seen one myself) from the reports - if that is, it is by accident and not by design.

But if you switch to a external view and look extremly flat over the ground, you notice that the lines are above the ground.


Let's try this again:

What you see on the screen is what the shader code renders, not what the underlyinh geometry is. That's different, because a vertex shader can displace things on the screen, a geometry shader can create new mesh parts, but the collision detection operates on the un-displaced original mesh. The taxiline flickering is addressed by such a fix - the line is displaced on the screen, but the geometry is still flat for collision detection.

In fact, the line is displaced based on your distance to it, so from the near-zone, it isn't much displaced at all, only when you're 100 meters away and the z-accuracy drops, it is moved more and more towards you.

That's the second advantage of a renderer-based fix over hard-coding this in the scenery mesh - you can dynamically react to the situation,

All textures (mostly alpha) that are used to paint on pavement (lines, numbers, signs, etc...) should have a priority higher than 0.


Why don't you look into how FG creates and textures a runway first and then explain us how it's done and what should be done? :D

The scenery developer dont need to rise the meshes of paintings.


And in fact they do not (I wonder if you realize at all that these lines are created automatically by TerraGear from airport description data).

So, if 2 or more textures have the same value in the z-buffer, the textures will be rendered in ascending order of the priority.


1) Textures have no value in the z-buffer, fragments have
2) Multiple textures are drawn on fragments as the fragment shader code says, not based on mysterious priorities
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Re: Taxiline Flickering Issue

Postby pb321 » Sun Sep 23, 2018 2:31 am

@psadro_gm,
Above you indicate:
The issue of taxi-lines 10s of cm above the pavement have been reported as well. These can bust your landing gear. I have a fix for this in the terragear toolchain, and will be available in a future scenery release.

I have developed an airport using Terragear and have experienced a similar problem with taxi lines above ground level. It doesn't break the landing gear but stops the plane or makes the plane move erratically when it is encountered. I'd like to fix it. How will I be able to obtain your fix? (compile a future version of Terragear, wait for the Docker tool chain or wait until the next scenery build? or some other way?). I'm very interested in fixing this issue in my local airport, so I'd like to learn more about how to get the fix when it is available. Is there any way to avoid the issue when creating an airport using an existing version of Terragear?
Thank you!
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