Hello, I think there's a glitch with using the itemstack-sensitive version of the Item#getIconIndex method.

 

What I'm attempting is using a different texture when a certain tag is true in the itemstack's NBT.

 

Picture:

As you can see, the icon in the hotbar changed but not the actual 3D item. Additionally, the item in 3rd person mod has the same texture still too.

 

Code:

package tf2crates.item;

import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;
import net.minecraft.client.renderer.texture.IIconRegister;
import net.minecraft.entity.EntityLivingBase;
import net.minecraft.entity.player.EntityPlayerMP;
import net.minecraft.item.ItemStack;
import net.minecraft.item.ItemSword;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.IIcon;
import tf2crates.ReferenceTC;
import tf2crates.ServerProxyTC;
import tf2crates.crate.RandomLoot;
import tf2crates.entity.DamageSourceBackstab;
import tlhpoeCore.network.MessagePlaySound;
import tlhpoeCore.util.MiscUtil;

public class ItemKnife extends ItemSword {
public static double backstabDifficulty = 0.75D;

public IIcon goldTexture;

public ItemKnife(String name) {
	super(ServerProxyTC.MOD_WEAPON);

	this.setUnlocalizedName(name);
	this.setTextureName(ReferenceTC.ID + ":weapon/" + name);

	RandomLoot.WEAPONS.add(this);
}

public ItemKnife(String name, float dmg) {
	this(name);

	MiscUtil.replaceField("field_150934_a", ItemSword.class, dmg, this);
}

@Override
@SideOnly(Side.CLIENT)
public void registerIcons(IIconRegister register) {
	super.registerIcons(register);

	this.goldTexture = register.registerIcon(ReferenceTC.ID + ":weapon/gold/" + this.getUnlocalizedName().substring(5));
}

@Override
@SideOnly(Side.CLIENT)
public IIcon getIconIndex(ItemStack itemStack) {
	NBTTagCompound nbt = itemStack.getTagCompound();

	if(nbt != null && nbt.getBoolean("Golden")) {
		return this.goldTexture;
	}

	return super.getIconIndex(itemStack);
}

@Override
public boolean hitEntity(ItemStack itemStack, EntityLivingBase prey, EntityLivingBase attacker) {
	itemStack.damageItem(1, attacker);

	float pYaw = prey.rotationYawHead % 360F;

	pYaw = pYaw < 0 ? 360 + pYaw : prey.rotationYawHead;

	float aYaw = attacker.rotationYawHead < 0 ? 360 + attacker.rotationYawHead : attacker.rotationYawHead;

	float newRot = pYaw - aYaw;

	if(newRot < (90 * backstabDifficulty) && newRot > (-90 * backstabDifficulty)) {
		if(!attacker.worldObj.isRemote) {
			new MessagePlaySound(ReferenceTC.ID + ":tf2crates.crit").sendTo((EntityPlayerMP) attacker);
		}

		attacker.heal(prey.getMaxHealth());
		prey.attackEntityFrom(DamageSourceBackstab.BACKSTAB, prey.getMaxHealth() * 600);
	}

	return false;
}
}

Inventory Icon (ItemIconIndex) is not equal (in terms of renderers) to Item 3d icon (ItemIcon). The itemstack-sensitive version is used to e.g make animated inventory icons (tho it should be made by resourcepacks).

 

Example from my mod:

@Override
public IIcon getIconIndex(ItemStack stack)
{
	if (stack.getTagCompound() != null) //should be more NBT checks here
	{
		return longswordIconStorage.get(stack.getTagCompound().getString("texture"));	
	}
	return this.itemIcon;
}

@Override
public IIcon getIcon(ItemStack stack, int pass)
{
	if (stack.getTagCompound() != null) //should be more NBT checks here
	{
		return longswordIconStorage.get(stack.getTagCompound().getString("texture"));	
	}
	return this.itemIcon;
}

 

Where longswordIconStorage is my Icon registry.

And this.itemIcon is my default Icon.