Skybox 2d-3d projection

UncleCrunch

I saw the Tutos on skybox and how to make it.
I see sometimes that images are a little stretched near the corners of the skybox.

Do we have to use a equi-rectangular image ? (see panorama software).

Or can we just make the 6 images and the engine will do the texture mapping coordinates itself ?
If so; then comes the seamless problem. Any experienced and talented guy for this ?

TIA

BeigeAlert

The skybox is just a simple cube, with simple square mappings. In order to keep it from looking like a square, you'll have to put a slight pincushion effect on the images. I've often pondered this, as some of the built in skyboxes even seem off in this way. I suppose if you wanted to make a perfect skybox, you'd need to ensure each image's horizontal and vertical field of view is EXACTLY 90 degrees, with no lens distortion. Assuming the image was photographed/rendered correctly, it should look right.

UncleCrunch

ok; say i get images rendered with a 3D tool like Blender and cameras are set to 90° angle, it should do it. Right ?

BeigeAlert

Yes, exactly.

Howser

I spent a good few weeks researching the process of making custom skyboxes. You do have plenty of options and tools out there to help you create skys for both the 3d and 2d model parts.
You've got the complete environmental scene generating software like DreamScape, Vue and Terrainagen, they're fairly powerful. There's a fairly interesting 3d terrain generator called world machine it is probably the most powerful/realistic terrain generator I've seen but the learning curve is bit steeper than the others. I decided against using them because they have this very distinctive, artificial look to the worlds they generate but a lot of people seem to use them for their skyboxes. The easiest way I found to convert a 3d environment into a 2d cube (in 3ds max only) is the wall worm helper called skywriter, get it here

There's also a fairly decent tutorial I found on stitching photos together if you decide to go that route, but requires 3ds max and z brush knowledge:


As for my own skybox; after researching and playing with these programs for a few weeks I decide to just stick to what I know. So I used zbrush for the terrain, baked down the lighting on the 3d model. Then used sky writer to render a basic metal ray 2d skybox which I just painted over in photoshop. The scene has two suns so this way the lighting for both the 2d and 3d skybox matched up.
I made two big mistakes with the 3d model, its too overbearing, having it lower down and further away would be much nicer visually. It also goes under the the player when it should just be a ring around the horizon line. You live and learn.

My advice is not to overwork the 2d skybox Its more about a setting the mood and the scene. 2d Skyboxes are never perfect and spark doesn't have the strongest feature set to help you realize the greater environment with. Using a composite method of big smooth colours/gradients and manipulated photos will probably do the trick just fine tbh. You can always do a lot of the 3d outer environment in the level itself. For the 3d skybox photos wrapped around on cylinders are also really effective done right. Again It doesn't have to be perfect as people will be more focused on the level design.

A note with using 3d skyboxes in spark; The skybox entity position in the world is relative to the players position. keep its origins as close to 0,0,0 in both the map and the cinematic editor or it wont be positioned correctly in the players view.

Hope that helped