Some of you may already be familiar with the limitation of cube-shaped skyboxen; the ugly seams visible between the cube faces. The technical issue behind the problem is a rather deep one and suffice to say, perfect solution is not available without DirectX 10 level of rendering engine if I recall correctly*
. However, things can be done to get over this issue, and today, after an IRC discussion on the subject, blowfish put together a model that uses a bit different mapping than the typical face=texture style that would seem logical and most straightforward to use. As a result, skyboxes with no seams can now be used with a generic skybox model, with a negligible texture resolution sacrifice.
This model can be, if desired, put inside the mediaVP starfield skysphere, and with alpha blended textures pretty much limitless amount of options is now available. Things like being in atmosphere, or having rings of a planet reach behind you, are now possible without seams and with supreme quality.
The mapping scheme used is as follows: When using texture resolution of 2048^2, the actual part of the texture mapped to the side of the cube is now 2040^2. The remaining edge of the texture space is used to border the texture with the corresponding edges from the textures next to it, which will negate the issue that caused the seam edge issue to begin with.
Here is a sample image of how to edit the textures to get the correct results in-game:
This is a 1024^2 texture, so the area used by the actual texture is 1020^2 and the two pixel border between is filled with adjacent sides' textures, as you can see from here. The darkened areas are shown here just for clarity.
In-game screenshots just for the hell of it (this skybox isn't especially high quality, since I just put it together for the purpose of testing the seamless skybox model):DOWNLOADS HERE
Here is a simple version to get the skybox and a batch of test maps:generic-skybox-redist.7z
And here is a more complete version that contains .xcf files (native GIMP format, PSD can be provided if requested) and the source 1024^2 textures for the sample skybox:generic-skybox-dev.7z
Maps: Hipshot @ www.zfight.com
, edited by Herra Tohtori, source image available at http://www.zfight.com/misc/images/textures/envmaps/stormydays_large.jpg
Enjoy your new seamless skyboxen, everyone!
As per discussion later in the thread, this turns out to be
partially incorrect. There is apparently a new feature that will be in 3.6.12 that will allow the use of standard six-side skybox cubes without the seam issues, by setting the skybox rendering to clamp the textures via a FRED flag. However, there are other issues associated to this method - mainly environmental mapping still suffering from the seams and dependancy on a graphics card that can actually do the required stuff.
The technique mentioned in this post is still applicable if you want to avoid envmapping issues or when using an older build that doesn't support the force clamp flag.