Heyall.

I’m writing a demo as part of an introductory course in OpenGL, and it includes a water surface. I managed to get a decent looking surface by creating a large, flat grid and then displacing its y coordinates with some sine and cosine functions. I calculated the normal for each vertex as the average height of the surrounding vertices. Worked nice, but was slow.

So I put it all into a shader. Everything works fine (and fast), except the normals. Since I only have access to the vertex I’m currently manipulating, I can’t calculate the normal by using the height of the surrounding vertices. The function I use to displace the vertex is too expensive to recalculate four times just to get the normal (it’s 0.30*(2.5 * sin(tfactor + (2*ecPos.x+ecPos.z)*PI/6.0) + 1.5 * sin(tfactor/2.0 + (-ecPos.z)*PI/11.0) -2.4 * cos(tfactor/5.0 + (ecPos.x-ecPos.z)*PI/8.0)) - yuck).

Any advice on how to proceed?