That depends on your definition of "horrible"

Seriously though, you can''t simulate realistic water without reflections and refractions, since those two components are the main properties of any transparent liquid.

But you can get something that a human observer will generally interprete as "watery", even without using reflections and/or refractions. Simple water as in Quake is easy, and doesn''t require any shader magic. Unfortunately, it''s not very attractive. You can get more or less acceptable water by using a simple transparent mesh displaced by your physics function. You''ll get a lot of sorting artifacts, but it''ll look like water. Specularity can help, but can quickly make your water look like a moving plastic plane.

I''d suggest you look at least into reflections. Even without refractions, water can look really good using reflections alone (either by a cubemap, or better by a projective render texture). You can perfectly do it on vertex level only, no pixel shaders are required to get a nice effect.

quote:Original post by d000hg
I presume the artifacts you refered to come from rendering transparent polys in the wrong order?

Yes.

quote:Original post by d000hg
How exactly do you do a cubemap for a sea? Is it not different than for a body (like the DX teapot)?

It's the same. You'll use a cubemap representing a large scale environment around your water surface. It's important that you don't add local geometry or details into the cubemap, because that will lead to artifacts (if you want local reflections, for example a boat, terrain, or some vegetation, then you'll have to use the render-texture approach). When rendering the water surface, you do this:

* bind the cubemap
* for each vertex, compute the reflection vector taking into account vertex position, normal, and view vector.
* use that reflection vector to index the cubemap.

You might want to add some blending, so the water gets semi transparent, otherwise you'll have a liquid metal look.

Once you have that working, you can attempt to add the so called Fresnel effect: that's the ratio of reflection to refraction, depending on the view angle. Instead of true refraction, you can simply modulate the transparency.

quote:Original post by d000hg
Something about rendering refraction has always puzzled me. When you look at a pixel/vertex you need to get the view-ray and bend it to a new angle and follow to see what it touches, right? But if the sea floor is not flat is it not very expensive to find the intersection of the ray and mesh? Or is this done totally differently?

As many other things in realtime 3D, you use an approximation here. The ocean floor (or any other object below the surface) is assumed flat. That makes the intersection calculations very easy. Since refraction is a visually very complex effect, the human brain will not notice physically inaccurate refractions, as long as the general behaviour is reasonably well approximated and the refraction index difference between liquid and air is not too big.

Refractions are generally either done by projective render textures, or by vertex deformation of the geometry below the water plane. Since they are almost always local, a cubemap approximation doesn't work very well for refractions.


[edited by - Yann L on June 9, 2004 4:28:54 PM]

i know you're thinking simple, but id start thinking "good implementation" and pair down from there. since Yann is aprticipating in this thread it reminds me of the lecture he gave on water.

Here
is a link to the lecture


Here is a link to Yann explaining some questions about it.


it's a good read, and is easily bastardized to an easier implementation if you decide that's too much

Dredd
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"To die with your sword still in its sheath is most regrettable" -- Miyomoto Musashi






[edited by - Dreddnafious Maelstrom on June 10, 2004 8:48:10 PM]