(Backport) Add support for rendering modded armor

# Conflicts:
#	src/main/java/com/minelittlepony/client/model/armour/PonifiedEquipmentRenderer.java
#	src/main/java/com/minelittlepony/client/render/entity/feature/ArmourFeature.java

src/main/java/com/minelittlepony/api/config/PonyConfig.java

@@ -77,6 +77,15 @@ public class PonyConfig extends Config {
                 .addComment("Disables certain easter eggs and secrets (party pooper)")
                 .addComment("Turning this off may help with compatibility in some cases");
 
+    public final Setting<Boolean> enableFabricModelsApiSupport = value("settings", "enableFabricModelsApiSupport", false)
+            .addComment("Enables rendering of modded armour registered via the fabric api")
+            .addComment("Note that since any armour registered in this way is designed to work for the human model, pieces may not fit exactly.")
+            .addComment("i.e. Anything that goes on the plyer's backs needs to be rotated by the mod developer when rendered on a pony")
+            .addComment("Developers: To know if you're being rendered on a pony model, check the renderstate or model class with")
+            .addComment(" state instanceof com.minelittlepony.api.model.PonyModel$AttributedHolder or model instanceof com.minelittlepony.api.model.PonyModel")
+            .addComment(" Note that the matrix stack your receieve is pre-transformed for the body part your model is attached to, so if you intend to call model.transform(state, part, matrices)")
+            .addComment(" with a different part (ie BACK) you must pop the stack to revert to the previous first.");
+
     public final Setting<VisibilityMode> horseButton = value("horseButton", VisibilityMode.AUTO)
                 .addComment("Whether to show the mine little pony settings button on the main menu")
                 .addComment("AUTO (default) - only show when HDSkins is not installed")

src/main/java/com/minelittlepony/client/render/entity/feature/ArmourFeature.java

@@ -8,9 +8,17 @@ import com.minelittlepony.common.util.Color;
 
 import java.util.*;
 
+import com.minelittlepony.api.config.PonyConfig;
+import com.minelittlepony.api.model.*;
+import com.minelittlepony.client.model.ClientPonyModel;
+import com.minelittlepony.client.util.render.MatrixStackUtil;
+
+import net.fabricmc.fabric.api.client.rendering.v1.ArmorRenderer;
+import net.fabricmc.fabric.impl.client.rendering.ArmorRendererRegistryImpl;
 import net.minecraft.client.render.*;
 import net.minecraft.client.render.entity.model.*;
 import net.minecraft.client.render.model.BakedModelManager;
+import net.minecraft.client.render.entity.model.BipedEntityModel;
 import net.minecraft.client.util.math.MatrixStack;
 import net.minecraft.component.DataComponentTypes;
 import net.minecraft.entity.EquipmentSlot;
@@ -18,8 +26,16 @@ import net.minecraft.entity.LivingEntity;
 import net.minecraft.item.*;
 import net.minecraft.item.trim.ArmorTrim;
 import net.minecraft.util.Colors;
+import net.minecraft.util.Unit;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 
 public class ArmourFeature<T extends LivingEntity, M extends EntityModel<T> & PonyModel<T>> extends AbstractPonyFeature<T, M> {
+    private static final Logger LOGGER = LogManager.getLogger("PonifiedEquipmentRenderer");
+
+    private static boolean FABRIC_API_FAILURE;
+
     public ArmourFeature(PonyRenderContext<T, M> context, BakedModelManager bakery) {
         super(context);
     }
@@ -56,6 +72,17 @@ public class ArmourFeature<T extends LivingEntity, M extends EntityModel<T> & Po
                 continue;
             }
 
+            if (!FABRIC_API_FAILURE && PonyConfig.getInstance().enableFabricModelsApiSupport.get()) {
+                try {
+                    if (FabricArmorRendererInvoker.renderArmor(stack, pony, matrices, provider, light, entity, armorSlot)) {
+                        continue;
+                    }
+                } catch (Throwable t) {
+                    LOGGER.error("Failure calling fabric armor rendering api", t);
+                    FABRIC_API_FAILURE = true;
+                }
+            }
+
             float glintAlpha = plugin.getGlintAlpha(armorSlot, stack);
             boolean glint = glintAlpha > 0;
             int color = plugin.getDyeColor(armorSlot, stack);
@@ -118,4 +145,43 @@ public class ArmourFeature<T extends LivingEntity, M extends EntityModel<T> & Po
 
         plugin.onArmourRendered(entity, matrices, provider, armorSlot, layer, ArmourRendererPlugin.ArmourType.ARMOUR);
     }
+
+
+    private static final class FabricArmorRendererInvoker {
+        private static final Map<ArmorRenderer, Unit> FAILING_RENDERERS = new WeakHashMap<>();
+
+        @SuppressWarnings({"rawtypes", "unchecked"})
+        private static <T extends LivingEntity, V extends ClientPonyModel<T>> boolean renderArmor(
+                ItemStack stack,
+                Models<T, ? extends PonyModel<T>> models, MatrixStack matrices,
+                VertexConsumerProvider vertices, int light, T entity,
+                EquipmentSlot armorSlot) {
+            ArmorRenderer renderer = ArmorRendererRegistryImpl.get(stack.getItem());
+
+            if (renderer != null && !FAILING_RENDERERS.containsKey(renderer)) {
+                MatrixStack isolation = MatrixStackUtil.pushIsolation(matrices);
+                try {
+                    isolation.push();
+                    models.body().transform(getBodyPart(armorSlot), isolation);
+                    renderer.render(isolation, vertices, stack, entity, armorSlot, light, (BipedEntityModel)models.body());
+                    isolation.pop();
+                } catch (Throwable t) {
+                    LOGGER.error("Exception occured whilst rendering custom armor via fabric api. Renderer {} has been disabled", renderer, t);
+                    FAILING_RENDERERS.put(renderer, Unit.INSTANCE);
+                } finally {
+                    MatrixStackUtil.popIsolation();
+                }
+                return true;
+            }
+            return false;
+        }
+
+        private static BodyPart getBodyPart(EquipmentSlot slot) {
+            return switch (slot) {
+                case HEAD -> BodyPart.HEAD;
+                case CHEST, BODY -> BodyPart.BODY;
+                case LEGS, FEET, MAINHAND, OFFHAND -> BodyPart.LEGS;
+            };
+        }
+    }
 }

src/main/java/com/minelittlepony/client/util/render/MatrixStackUtil.java

@@ -0,0 +1,19 @@
+package com.minelittlepony.client.util.render;
+
+import net.minecraft.client.util.math.MatrixStack;
+
+public class MatrixStackUtil {
+    static final MatrixStack ISOLATION_STACK = new MatrixStack();
+
+    public static MatrixStack pushIsolation(MatrixStack matrices) {
+        ISOLATION_STACK.peek().getNormalMatrix().set(matrices.peek().getNormalMatrix());
+        ISOLATION_STACK.peek().getPositionMatrix().set(matrices.peek().getPositionMatrix());
+        return ISOLATION_STACK;
+    }
+
+    public static void popIsolation() {
+        while (!ISOLATION_STACK.isEmpty()) {
+            ISOLATION_STACK.pop();
+        }
+    }
+}

src/main/resources/assets/minelittlepony/lang/en_us.json

@@ -14,6 +14,7 @@
   "minelp.options.skins.hdskins.open": "Open HD Skins",
   "minelp.options.skins.hdskins.disabled": "HD Skins is not installed\n\nThe HD Skins mod is required to upload skins from in-game and to use custom skin servers.\n\nIf you cannot use that you will have to go to www.minecraft.net to upload your skin there.",
   "minelp.options.snuzzles": "Show Snuzzles",
+  "minelp.options.enablefabricmodelsapisupport": "(Experimental) Show Modded Armor",
   "minelp.options.fillycam": "Filly Cam",
   "minelp.options.showscale": "Show-accurate scaling",
   "minelp.options.fpsmagic": "Magic in first-person",