Apologies if this is a FAQ, but i would like to know the fastest way to implement a user-defined clip plane for the PowerVR SGX. The Water demo (https://www.imgtec.com/powervr/insider/docs/POWERVR.Shader%20Based%20Water%20Effects.1.11f.OGLES2External.pdf section 3.1) uses a technique which appears to be the same as one documented by Eric Lengyel (http://www.terathon.com/lengyel/Lengyel-Oblique.pdf), but the OpenGL ES 2 spec recommends:
User clip planes can be emulated by calculating the dot product of the user clip plane with the vertex position in eye space in the vertex shader
The second method seems simpler, and more likely to be portable. Is the Water demo mechanism significantly faster? I’ll be digging into this shortly, but just wondered if anyone had experience with this.