Water distortions

[IntegratedQuantum]

Possible implementation:

1. Draw all transparent blocks further away than ~100 blocks or so normally (to reduce vertex shader invocations, the effect would be disabled in the distance)
2. Rasterize all distortable transparent blocks to a depth buffer to find the first layer.
3. Render all transparent blocks behind that first layer (GL_GREATER) normally.
4. Copy everything (everything that's behind the distortable layer) into a new framebuffer (half resolution to reduce bandwidth?)
5. Render the distortable first layer (GL_EQUAL) with a special shader using the new framebuffer as a source for distortions.
6. Render all transparent blocks before that first layer (GL_EQUAL) normally.

The fact that it would be limited to only the first layer should not be noticable (hopefully). Extending it to more layers would require an unbearable amount of additional passes.