Water

On this example, i added a reflective water effect. The theory behind is very well explained on a article on gamedev.net by Yann Lombard ( http://www.gamedev.net/columns/hardcore/rnerwater1/ ). The algorithm is the following :

1. clip the upper-half part of the world (clip with the water plane), inverse it according to the plane of the water and render it in a texture. Let's call that texture waterTexture.
2. clip the under-water part of the world and render it in the same texture waterTexture, but with a transparency coefficient.
3. render the water mesh by projecting waterTexture on it :
   1. calculate the normal at every vertex of the water, according to a wave model. I have chosen a very basic sine model because it gives the normal very easily.
   2. let's call P.xyz the coordinates of the vertex. Instead of passing P to the projective matrix to get the texture coordinates onto waterTexture, we displace P on the plane of the water according to the projection of the normal on this plane.
   3. project the waterTexture onto this plane mesh.
4. render the moutains

Details :

• In my program, clipping is done in the HLSL pixel shader, knowing the altitude of every fragment. This is GPU-consuming but precise.
• Sky is achieved with a basic skybox
• The frame rate is about 50 image per second, but it can be optimized. For this program, i wanted to get the best results in term of quality... For example, the terrain rendered into a texture for the reflection is very-high quality, with shadow and so on... and that's pretty useless and it costs much. And i have to render it twice into this texture (first for the upper-part of the world, then for the under-water part).

The following pictures are going with the options i have incrementaly added. First ones are pretty simple and the last one is the more advandced. Of course, the animation of the water is better to see in real-time that on screenshots, but i need to optimize a bit the program...

Download

download  : water.ace ( 2302ko) (exe+source+projet Visual C++ 6.0)

download : water.ace ( 2225ko) executable version with MFC to set up parameters (shadow, transparency, wave model...)

Screenshots Gallery

overview of the results ( reflective water and transparency, no clouds, water is not disturbed)

water is too transparent here, it's hard to get what is reflection and what is the under-water ground ( reflective water and transparency, no clouds, water is not disturbed)

water is very reflective here and hardly not transparent ( reflective water and transparency, no clouds, water is not disturbed)

water is at the maximum of reflection, details of the moutains in the water are well represented ( reflective water, no transparency , no clouds, water is not disturbed)

water is at the maximum of transparency, the green texture of the under-water part is good looking ( reflective water and transparency, no clouds, water is not disturbed)

same as previous one but with a bit less transparency ( reflective water and transparency, no clouds, water is not disturbed)

reflected sky ( water is purely reflective here), in the upper-left corner, one can notive an edge of the sky-box. ( reflective water and clouds, no transparency,  water is not disturbed)

the almost final picture : tranparency, reflection (mountains and sky), shadow... ( reflective water and transparency, clouds, water is not disturbed)

zoom on a fine part, one can notice an artefact on the left side of this picture, where water is meeting the mountains, some pixels are visible... ( reflective water and transparency, clouds, water is not disturbed)

one can notice here that the reflection is perturbated.

evrything is turned on, except that under-water part is not perturbated

on this picture, i add perturbations to the under-water part

the final picture : everything is turned on

a little problem : because coordinates are perturbated before being passed to the projective matrix, this blue-sky pixels appear.

To correct this, i set the clipping plane a bit under the water plane when rendering the inversed upper-side of the world

Author :  Adrien Auclair  
adrien.auclair at club-internet.fr
Last update : 15/10/2004