View Full Version : skybox and horizon
08-11-2002, 02:26 PM
When I move camera I see how distant mountains appear. This looks terrible. So I added fog and clear color buffer with color of fog. It was better.
But then I created skybox. I painted sky texture and draw 4 big quads. Now I see appearing mountains again.
How can I fix horizon problem? I don't want to model whole planet (sphere).
The easiest thing to do is to make the skybox fade to a single color at the horizon, so that you can still use a single fog color to fade the terrain into the distance.
There are other ways of dealing with the issue, but I don't want to go into too much depth if the above will solve your problem.
08-11-2002, 05:43 PM
Hello Zeno, you wrote:
"The easiest thing to do is to make the skybox fade to a single color at the horizon, so that you can still use a single fog color to fade the terrain into the distance."
It isn't possible, my mountains are high. Please see screenshots on http://decopter.sf.net.
Jeffry J Brickley
08-12-2002, 10:49 AM
darn, why not draw the whole planet? save me some work doing it. http://www.opengl.org/discussion_boards/ubb/wink.gif http://www.opengl.org/discussion_boards/ubb/wink.gif
sounds like your fog got turned off again, try making sure your order of operations are set right so that you use both fog and skybox with as the other message said, the skybox color disolving into the same fog color so the two blend on the horizon.
Jeffry J Brickley
08-12-2002, 10:53 AM
actually, in rereading your posts, sounds like your land coverage may be too small. You want enough distance between you and the terrain coming in that you minimize the appearence, then you can use the tricks mentioned to bring clear them up in the distance as perspective shrinks them.
I run about 50km out of date for paging in near ground level, more at higher altitude, that seems to work well in perspective.
08-12-2002, 11:52 AM
hello Jeffry, you wrote:
"I run about 50km out of date for paging in near ground level, more at higher altitude, that seems to work well in perspective."
1. How small is distance between points on your heightmap? I use 10m to 100m.
2. What LOD method you are using? I started from ROAM, but then I decided to build binary triangle tree independent of view at begin, then draw same stuff every frame (no LOD at all).
3. What happen when you use 16-bit zbuffer?
u cant really fog skyboxes (well u can but u get ****ty results, even using a dome still aint gonna give nice results)
ive done a bit of work with this in the past + my conclusion
u cant do fog + skyboxes together!
its as spock would say 'illogical'
08-12-2002, 01:18 PM
I've done something sortof like a depth dependent alpha blend. It worked like this. First I drew the skybox as usual. Then I drew all the scene geometry (triangles) near to far. For those that were beyond some distance from the near plane, I enabled alpha blending and used alpha values that were dependent to the distance in some manner (much like fog). I left depth testing enabled using a depth test of GL_LESS. In this way the far removed objects would blend with the sky, but not each other.
Jeffry J Brickley
08-14-2002, 05:46 AM
We have used a variety of meshes, ROAM, base quadtree, etc. I am leaning towards ROAM and bintree type meshes more and more. however, right now we used a terrapage lod system, expensive to build landscapes, I am trying to find viable technology to move away from those huge datasets.
I have successfully adapted Xterra (search the histories here, or at vterrain.org) and ROAM to fairly large areas (300km) at 30m. The write up on the Demeter terrain engine says it is capable of paging terrain sets, it's on my list to evaluate, as is SOAR released from Peter Lindstrom's work on landscapes.
16 bit depth buffer is going to be tricky, there are serious noticeable geometry effects with 16 bit z-buff, especially when the background earth is enabled for space-to-your face. I don't use fog or skyboxes except in demos, I have never liked hiding paging effects, so you might listen to the better experts here, I was only offering suggestions. I try to set things so that they only page at low altitude and quickly run to lowest LOD and stay there for high altitude. It also has to adapt to extemely rapid movement (a severe failure in Xterra's original code, but can be fixed relatively easily). I fear I deal with real-world datasets, so I only deal with realistic elevations which is both help and hindrance at times.
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