protected void startCondition(String condition, StringBuilder source) {
        if (condition != null) {
            appendIndent(source);
            source.append("#if ");
            source.append(condition);
            source.append("\n");
            indent();
        }
    }
Starts a conditional block
@param condition the block condition
@param source the StringBuilder to use
jme3-core/src/main/java/com/jme3/shader/Glsl100ShaderGenerator.java