protected void declareVarying(StringBuilder source, ShaderNodeVariable var, boolean input) {
        declareVariable(source, var, true, "varying");
    }
Declares a varying
@param source the StringBuilder to use
@param var the variable to declare as a varying
@param input a boolean set to true if the varying is an input.
This in not used in this implementation, but can be used in overriding
implementations.
jme3-core/src/main/java/com/jme3/shader/Glsl100ShaderGenerator.java