   Can't use clip() in Cg fragment shader
  I am trying to use the clip() function in a fragment shader:float4 temp = float4(0.0,0.0,-2.0,0.0);clip(temp); But I just get the error:fp_test.cg(53) : error C1115: unable to find compatible overloaded function "clip(float4)"But in the Cg reference manual it says:NAMEclip − conditionally kill a pixel before outputSYNOPSISvoid clip(float4 x);PARAMETERSx Vector condition to clip onDESCRIPTIONkills the current pixel output if any component of the given vector is negativeSo why do I get the error?   