A lot of things

Redid most of the mod, to make compatibility even more likely. Hitbox swapping works. Basically I figured out why the arms weren't swapping before; the boxes used display lists. So I swap the display list it uses depending on the render job.
However Smart Moving once again found a way to explode. Wide arm models actually 100% work but slim arm ones do not... The right arm is messed up, albeit the hat layer actually gets "slimmed" properly... What will it take, Smart Moving?! So close, yet so far.
Renamed some interfaces to more accurately describe what they do, and done some preparations to make the ModelBiped mixin apply to all biped entities for better scope and detection.
Twilight Forest giants now work. For now they get assigned a default skin; this won't remain the default behavior for long, but it will be a config option.
Lots of new Utils, including splitting off the settings for several transformations into an enum. Hey, seems unnecessary but I got tired of messing with so many branching utility funcs whenever I needed to pass in a new setting, okay?!
The new utils allowed the mixin rewrite to be a lot cleaner.
Default skin state is set on player instantiation instead of every frame.
Slim Steve no longer has hat layer on arms and also has corrected UV mappings from before.

Signed-off-by: roadhog360 <[email protected]>

Author: Roadhog360

README.md

@@ -16,13 +16,14 @@ Current Features:
 - Fix overlap in hat layer when wearing a head
 - Hat layers on head blocks
 - New default skins alongside just Steve
+- Patch for Twilight Forest giants
 
 Todo:
 - Config
   - Toggle head block inventory icon render
   - Toggle new default skins (Either Steve/Alex or JUST Steve)
 
 Current incompatibility todo:
-- Twilight Forest giants
-- Smart Moving
+- Twilight Forest heads
+- Smart Moving (it's like 90% working slim models are just slightly wrong)
 - Botania Gaia Guardian

dependencies.gradle

@@ -35,5 +35,6 @@
  */
 dependencies {
     runtimeOnlyNonPublishable("com.github.GTNewHorizons:NotEnoughItems:2.5.4-GTNH:dev")
+    compileOnly('com.github.GTNewHorizons:twilightforest:2.6.33:dev')
     compileOnly deobfCurse("headcrumbs-222838:2279949")
 }

src/main/java/roadhog360/simpleskinbackport/ClientProxy.java

@@ -3,7 +3,7 @@
 import cpw.mods.fml.common.FMLCommonHandler;
 import cpw.mods.fml.common.event.FMLInitializationEvent;
 import net.minecraftforge.common.MinecraftForge;
-import roadhog360.simpleskinbackport.core.ClientEventHandler;
+import roadhog360.simpleskinbackport.client.ClientEventHandler;
 
 public class ClientProxy extends CommonProxy {
 

src/main/java/roadhog360/simpleskinbackport/core/ClientEventHandler.java renamed to src/main/java/roadhog360/simpleskinbackport/client/ClientEventHandler.java

@@ -1,19 +1,21 @@
-package roadhog360.simpleskinbackport.core;
+package roadhog360.simpleskinbackport.client;
 
 import cpw.mods.fml.client.FMLClientHandler;
 import cpw.mods.fml.common.eventhandler.SubscribeEvent;
+import net.minecraft.client.model.ModelBiped;
 import net.minecraft.client.renderer.entity.Render;
+import net.minecraft.client.renderer.entity.RenderBiped;
 import net.minecraft.client.renderer.entity.RenderManager;
 import net.minecraft.client.renderer.entity.RenderPlayer;
 import net.minecraft.entity.Entity;
-import net.minecraft.entity.player.EntityPlayer;
+import net.minecraft.entity.EntityLiving;
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemSkull;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.client.event.RenderHandEvent;
 import net.minecraftforge.client.event.RenderLivingEvent;
-import roadhog360.simpleskinbackport.ducks.INewModelData;
-import roadhog360.simpleskinbackport.ducks.ISwitchableArmsModel;
+import roadhog360.simpleskinbackport.ducks.IArmsState;
+import roadhog360.simpleskinbackport.ducks.INewBipedModel;
 
 public class ClientEventHandler {
     public static final ClientEventHandler INSTANCE = new ClientEventHandler();
@@ -25,15 +27,27 @@ public void onHandRender(RenderHandEvent event) {
     @SubscribeEvent
     public void onRenderEntity(RenderLivingEvent.Pre event) {
         checkAndSetArmsState(event.entity, event.renderer);
-        if(event.renderer instanceof RenderPlayer renderPlayer && event.entity instanceof EntityPlayer living) {
+        if(event.entity instanceof EntityLiving living) {
             ItemStack itemstack = living.getEquipmentInSlot(4);
-            renderPlayer.modelBipedMain.bipedHeadwear.showModel = itemstack == null || !isHead(itemstack.getItem());
+            boolean showHeadwear = itemstack == null || !isHead(itemstack.getItem());
+            if(event.renderer instanceof RenderPlayer renderPlayer) {
+                renderPlayer.modelBipedMain.bipedHeadwear.showModel = showHeadwear;
+            } else if (event.renderer instanceof RenderBiped renderBiped) {
+                renderBiped.modelBipedMain.bipedHeadwear.showModel = showHeadwear;
+            }
         }
     }
 
     private void checkAndSetArmsState(Entity entity, Render render) {
-        if(render instanceof RenderPlayer renderPlayer && renderPlayer.modelBipedMain instanceof ISwitchableArmsModel model
-            && entity instanceof INewModelData player) {
+        ModelBiped modelBiped;
+        if(render instanceof RenderPlayer renderPlayer) {
+            modelBiped = renderPlayer.modelBipedMain;
+        } else if (render instanceof RenderBiped renderBiped) {
+            modelBiped = renderBiped.modelBipedMain;
+        } else {
+            return;
+        }
+        if(modelBiped instanceof INewBipedModel model && entity instanceof IArmsState player) {
             model.simpleSkinBackport$setSlim(player.simpleSkinBackport$isSlim());
         }
     }

src/main/java/roadhog360/simpleskinbackport/client/ImageBufferDownloadPlayerSkin.java

@@ -4,7 +4,7 @@
 import net.minecraft.client.renderer.ImageBufferDownload;
 import net.minecraft.client.resources.SkinManager;
 import roadhog360.simpleskinbackport.core.Utils;
-import roadhog360.simpleskinbackport.ducks.INewModelData;
+import roadhog360.simpleskinbackport.ducks.IArmsState;
 
 import java.awt.*;
 import java.awt.image.BufferedImage;
@@ -64,7 +64,7 @@ public BufferedImage parseUserSkin(BufferedImage buffImg) {
     @Override
     public void func_152634_a() {
         super.func_152634_a();
-        if(callback instanceof INewModelData data) {
+        if(callback instanceof IArmsState data) {
             Utils.setSlimFromMetadata(texture, data);
         }
     }

src/main/java/roadhog360/simpleskinbackport/client/models/ModelHatLayer.java

@@ -0,0 +1,51 @@
+package roadhog360.simpleskinbackport.core;
+
+import com.google.common.collect.Lists;
+import net.minecraft.client.model.ModelBox;
+import net.minecraft.client.model.ModelRenderer;
+import org.apache.commons.lang3.tuple.Pair;
+
+import java.util.List;
+
+public class ArmPair extends Pair<List<ModelBox>, List<ModelBox>> {
+
+    private final List<ModelBox> left;
+    private final Integer leftDisplayList;
+    private final List<ModelBox> right;
+    private final Integer rightDisplayList;
+
+    private ArmPair(List<ModelBox> left, Integer leftDisplayList, List<ModelBox> right, Integer rightDisplayList) {
+        this.left = left;
+        this.leftDisplayList = leftDisplayList;
+        this.right = right;
+        this.rightDisplayList = rightDisplayList;
+    }
+
+    public static ArmPair of(ModelRenderer left, ModelRenderer right) {
+        return new ArmPair(Lists.newArrayList(left.cubeList), Utils.createDisplaylistFor(left),
+            Lists.newArrayList(right.cubeList), Utils.createDisplaylistFor(right));
+    }
+
+    @Override
+    public List<ModelBox> getLeft() {
+        return left;
+    }
+
+    public Integer getLeftDisplayList() {
+        return leftDisplayList;
+    }
+
+    @Override
+    public List<ModelBox> getRight() {
+        return right;
+    }
+
+    public Integer getRightDisplayList() {
+        return rightDisplayList;
+    }
+
+    @Override
+    public List<ModelBox> setValue(List<ModelBox> value) {
+        throw new UnsupportedOperationException();
+    }
+}