How are the following 3D effects mocked in Myst 4? (link)

Question

Superficially, I thought 'all' that would be required to make a myst style game would be to place the camera inside a 3D sphere, with the sphere's inner surface textured with an appropriately-distorted (to account for the concave nature of the sphere), 2D rendering of a 3D world.

The only thing that I can't really work out is how are some elements of the game alive and moving?

In this video, the sea waves are moving: http://www.youtube.com/watch?v=ju0lACSm7Us

In this one we have some pretty cool particle effects involving clouds, as well as lighting, thought I think the lightning is pre-rendered: http://www.youtube.com/watch?v=_CidCIDHFL4

I doubt these effects are actually 3D; I think they are 2D looping movie files. However I could be wrong.

To clarify, how do you think they've achieved such gorgeous 3D effects regarding the water, clouds and lightning?

Are they looping movies? How are these movies presented to the user and integrated so well?

Answer 1

One way to make such an effect is UV animation.

The UV is a texture coordinates, as XYZ is the objects coordinates, what is done here is simple. Given the following texture with the mention that it needs to have an alpha channel so that we can exclude the blue color and leave just the clouds, it is going to be applied to a quad

Let the upper left corner be (0,0) in texture coordinates be the starting poing. What it is being done: a step X is taken and the starting point of the UV texture is incremented at each frame/update giving the illusion of animation.

To achieve different effects, different textures are "displaced", for the clouds the diffuse texture, for the water the normal texture given it is a flat quad with only reflection.

For the lightning it's just a simple texture with alpha and perhaps some additional calculations being done in the fragment shader.