minecraft-kajetans-text-core-mod/src/main/resources/class_transformer/font_renderer.js

var transformerName = "Font Renderer Transformer";
var ASMAPI = Java.type('net.minecraftforge.coremod.api.ASMAPI');
var Opcodes = Java.type('org.objectweb.asm.Opcodes');
var MethodInsnNode = Java.type("org.objectweb.asm.tree.MethodInsnNode");
var FieldInsnNode = Java.type("org.objectweb.asm.tree.FieldInsnNode");

function initializeCoreMod() {
    return {
        transformerName: {
            'target': {
                'type': 'CLASS',
                'name': 'net.minecraft.client.gui.FontRenderer'
            },
            'transformer': function (classNode) {
                var methods = classNode.methods;
                
                var targetMethodName = ASMAPI.mapMethod("func_228081_c_"); // renderStringAtPos
                var targetMethodDesc = "(Ljava/lang/String;FFIZLnet/minecraft/client/renderer/Matrix4f;Lnet/minecraft/client/renderer/IRenderTypeBuffer;ZII)F";                

                for (var i in methods) {
                    var method = methods[i];
                    if (method.name.equals(targetMethodName) && method.desc.equals(targetMethodDesc)) {
                        print(method.name + " " + method.desc);
                        transform(method);
                        break;
                    }
                }
                return classNode;
            }
        }
    };
}

function transform(method) {
    var instrList = method.instructions;
    
    for (var i = 0; i < instrList.size(); ++i) {
        var instr = instrList.get(i);
        if(instr instanceof MethodInsnNode && instr.owner.equals("net/minecraft/util/text/TextFormatting")) {
            instrList.remove(instr);
            instrList.insert(instrList.get(i - 1), new MethodInsnNode(instr.getOpcode(), "me/ktcm/ModTextFormatting", 
                ASMAPI.mapMethod(instr.name), instr.desc.replace("net/minecraft/util/text/TextFormatting", "me/ktcm/ModTextFormatting"), false));
        } else if(instr instanceof FieldInsnNode && instr.owner.equals("net/minecraft/util/text/TextFormatting")) {
            instrList.remove(instr);
            instrList.insert(instrList.get(i - 1), new FieldInsnNode(instr.getOpcode(), "me/ktcm/ModTextFormatting", 
                ASMAPI.mapField(instr.name), instr.desc.replace("net/minecraft/util/text/TextFormatting", "me/ktcm/ModTextFormatting")));
        }
    }
}