OpenGL water refraction

I'm trying to create an OpenGL application with water waves and refraction. I need to either cast rays from the sun and then the camera and figure out where they intersect, or I need to start from the ocean floor and figure out in which direction(s, if any) I have to go in order to hit the sun or the camera. I'm kind of stuck, can any one give me an inpoint into either OpenGL ray casting or a crash course in advanced geometry? I don't want the ocean floor to 开发者_如何学编程be at a constant depth and I don't want the water waves to be simple sinusoidal waves.

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First things first: The effect you're trying to achieve can be implemented using OpenGL, but it is not a feature of OpenGL. OpenGL by itself is just a sophisticated triangle to screen drawing API. You got some input data and write a program that performs relatively simple rasterizing drawing operations based on the input data using the OpenGL API. Shaders give it some space; you can implement a raytracer in the fragment shader.

In your case that means, you must implement a some algorithm that generates a picture like you intend. For water is must be some kind of raytracer or fake refraction method to get the effect of looking into the water. The caustics require either a full features photon mapper, or you're good with a fake effect based on the 2nd derivative of the water surface.

There is a WebGL demo, rendering stunningly good looking, interactive water: http://madebyevan.com/webgl-water/ And here's a video of it on YouTube http://www.youtube.com/watch?v=R0O_9bp3EKQ

This demo uses true raytracing (the water surface, the sphere and the pool are raytraced), the caustics are a "fake caustics" effect, based on projecting the 2nd derivative of the water surface heightmap.

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There's nothing very OpenGL-specific about this.

Are you talking about caustics? Here's another good Gamasutra article.

Reflections are normally achieved by reflecting the camera in the plane of the mirror and rendering to a texture, you can apply distortion and then use it to texture the water surface. This only works well for small waves.

What you're after here is lots of little ways to cheat :-)

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Techincally, all you perceive is a result of lightwaves/photons bouncing off the surfaces and propagating through mediums. For the "real deal" you'll have to trace the light directly from the Sun with each ray following the path:

• hit the water surface
• refract+reflect, reflected goes into the camera(*), refracted part goes further
• hits the ocean bottom
• reflects
• hits the water from beneath
• reflect+refracts, refracted part gets out of the water and hits the camera(*), reflected again goes to the ocean bottom, reflects etc.

(*) Actually, most of the rays will miss the camera, but that will be overly expensive, so this is a cheat.

Do this for at least three wavelengths - "red", "green" and "blue". Each of them will refract and reflect differently. You'll get the whole picture by combining the three.

Then you just create a texture with the rays that got into the camera and overlay it in OpenGL.

That's a straighforward, simple and very computationally expensive way that gives an approximation to the physics beyond the caustics.