Properly render both arms in first person when holding an entity

src/main/java/com/minelittlepony/unicopia/client/FirstPersonRendererOverrides.java

@@ -0,0 +1,32 @@
+package com.minelittlepony.unicopia.client;
+
+import java.util.Optional;
+
+import com.minelittlepony.unicopia.client.render.AccessoryFeatureRenderer;
+import com.minelittlepony.unicopia.entity.player.Pony;
+
+import net.minecraft.client.network.ClientPlayerEntity;
+import net.minecraft.client.render.VertexConsumerProvider;
+import net.minecraft.client.render.item.HeldItemRenderer;
+import net.minecraft.client.util.math.MatrixStack;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.util.Arm;
+
+public class FirstPersonRendererOverrides {
+    public static final FirstPersonRendererOverrides INSTANCE = new FirstPersonRendererOverrides();
+
+    public Optional<HeldItemRenderer.HandRenderType> getHandRenderType(PlayerEntity player) {
+        return Pony.of(player).getEntityInArms().map(e -> HeldItemRenderer.HandRenderType.RENDER_BOTH_HANDS);
+    }
+
+    public boolean beforeRenderHands(ArmRenderer sender, float tickDelta, MatrixStack matrices, VertexConsumerProvider.Immediate vertexConsumers, ClientPlayerEntity player, int light) {
+        var root = AccessoryFeatureRenderer.FeatureRoot.of(player);
+        return root != null && root.getAccessories().beforeRenderArms(sender, tickDelta, matrices, vertexConsumers, player, light);
+    }
+
+    public interface ArmRenderer {
+        void invokeRenderArmHoldingItem(MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, float equipProgress, float swingProgress, Arm arm);
+
+        float getEquipProgress(float tickDelta);
+    }
+}

src/main/java/com/minelittlepony/unicopia/client/render/AccessoryFeatureRenderer.java

@@ -1,9 +1,14 @@
 package com.minelittlepony.unicopia.client.render;
 
-import java.util.ArrayList;
+import java.util.*;
-import java.util.List;
 
+import org.jetbrains.annotations.Nullable;
+
+import com.minelittlepony.unicopia.client.FirstPersonRendererOverrides.ArmRenderer;
+
+import net.minecraft.client.MinecraftClient;
 import net.minecraft.client.model.ModelPart;
+import net.minecraft.client.render.VertexConsumer;
 import net.minecraft.client.render.VertexConsumerProvider;
 import net.minecraft.client.render.entity.feature.FeatureRenderer;
 import net.minecraft.client.render.entity.feature.FeatureRendererContext;
@@ -39,6 +44,14 @@ public class AccessoryFeatureRenderer<
         features.forEach(feature -> feature.renderArm(matrices, vertexConsumers, light, entity, arm, side));
     }
 
+    public boolean beforeRenderArms(ArmRenderer sender, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, T entity, int light) {
+        boolean cancelled = false;
+        for (var feature : features) {
+            cancelled |= feature.beforeRenderArms(sender, tickDelta, matrices, vertexConsumers, entity, light);
+        }
+        return cancelled;
+    }
+
     public interface FeatureFactory<T extends LivingEntity> {
         Feature<T> create(FeatureRendererContext<T, ? extends BipedEntityModel<T>> context);
     }
@@ -46,7 +59,10 @@ public class AccessoryFeatureRenderer<
     public interface Feature<T extends LivingEntity> {
         void render(MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, T entity, float limbAngle, float limbDistance, float tickDelta, float animationProgress, float headYaw, float headPitch);
 
-        default void renderArm(MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, T entity, ModelPart arm, Arm side) {
+        default void renderArm(MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, T entity, ModelPart arm, Arm side) {}
+
+        default boolean beforeRenderArms(ArmRenderer sender, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, T entity, int light) {
+            return false;
         }
     }
 
@@ -54,5 +70,14 @@ public class AccessoryFeatureRenderer<
             T extends LivingEntity,
             M extends BipedEntityModel<T>> {
         AccessoryFeatureRenderer<T, M> getAccessories();
+        @SuppressWarnings("unchecked")
+        @Nullable
+        static <T extends LivingEntity, M extends BipedEntityModel<T>> FeatureRoot<T, M> of(T entity) {
+            var renderer = MinecraftClient.getInstance().getEntityRenderDispatcher().getRenderer(entity);
+            if (renderer instanceof FeatureRoot) {
+                return (FeatureRoot<T, M>)renderer;
+            }
+            return null;
+        }
     }
 }

src/main/java/com/minelittlepony/unicopia/client/render/HeldEntityFeatureRenderer.java

@@ -1,5 +1,6 @@
 package com.minelittlepony.unicopia.client.render;
 
+import com.minelittlepony.unicopia.client.FirstPersonRendererOverrides.ArmRenderer;
 import com.minelittlepony.unicopia.client.minelittlepony.MineLPDelegate;
 import com.minelittlepony.unicopia.entity.Living;
 import com.minelittlepony.unicopia.entity.duck.EntityDuck;
@@ -20,7 +21,10 @@ import net.minecraft.util.math.*;
 
 public class HeldEntityFeatureRenderer<E extends LivingEntity> implements AccessoryFeatureRenderer.Feature<E> {
 
+    private final FeatureRendererContext<E, ? extends BipedEntityModel<E>> context;
+
     public HeldEntityFeatureRenderer(FeatureRendererContext<E, ? extends BipedEntityModel<E>> context) {
+        this.context = context;
     }
 
     @Override
@@ -47,23 +51,37 @@ public class HeldEntityFeatureRenderer<E extends LivingEntity> implements Access
 
     @Override
     public void renderArm(MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, E entity, ModelPart arm, Arm side) {
-        Pony.of(entity).flatMap(Pony::getEntityInArms).ifPresent(passenger -> {
-            float tickDelta = MinecraftClient.getInstance().getTickDelta();
 
+    }
+
+    @Override
+    public boolean beforeRenderArms(ArmRenderer sender, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, E entity, int light) {
+        return Pony.of(entity).flatMap(Pony::getEntityInArms).filter(passenger -> {
+            float swingProgress = entity.getHandSwingProgress(MinecraftClient.getInstance().getTickDelta());
+            float f = -0.4f * MathHelper.sin(MathHelper.sqrt(swingProgress) * (float)Math.PI);
+            float g = 0.2f * MathHelper.sin(MathHelper.sqrt(swingProgress) * ((float)Math.PI * 2));
+            float h = -0.2f * MathHelper.sin(swingProgress * (float)Math.PI);
             matrices.push();
-            matrices.translate(0.8F, 0.4F, -0.1F);
+            matrices.translate(f, g, h);
-            matrices.multiply(RotationAxis.POSITIVE_Y.rotationDegrees(90));
+            matrices.translate(0, -1.3F, -1.3F);
-            matrices.multiply(RotationAxis.POSITIVE_X.rotationDegrees(-60 - 13));
+            matrices.multiply(RotationAxis.POSITIVE_X.rotationDegrees(13));
-            matrices.multiply(RotationAxis.POSITIVE_Z.rotationDegrees(-30));
-            matrices.translate(0, 0, -0.2F);
             if (!(passenger instanceof Pony)) {
                 matrices.multiply(RotationAxis.POSITIVE_Y.rotationDegrees(90));
             }
-            matrices.translate(-passenger.asEntity().getWidth() / 16F, 0.3F, 0);
 
             renderCarriedEntity(passenger.asEntity(), matrices, vertexConsumers, light, tickDelta);
             matrices.pop();
-        });
+
+            float equipProgress = 1 - sender.getEquipProgress(tickDelta);
+
+            matrices.push();
+            sender.invokeRenderArmHoldingItem(matrices, vertexConsumers, light, equipProgress, swingProgress, Arm.LEFT);
+            matrices.pop();
+            matrices.push();
+            sender.invokeRenderArmHoldingItem(matrices, vertexConsumers, light, equipProgress, swingProgress, Arm.RIGHT);
+            matrices.pop();
+            return true;
+        }).isPresent();
     }
 
     private void renderCarriedEntity(LivingEntity p, MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, float tickDelta) {

src/main/java/com/minelittlepony/unicopia/mixin/client/MixinHeldItemRenderer.java

@@ -0,0 +1,58 @@
+package com.minelittlepony.unicopia.mixin.client;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.gen.Invoker;
+import org.spongepowered.asm.mixin.injection.*;
+import org.spongepowered.asm.mixin.injection.At.Shift;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import com.minelittlepony.unicopia.client.FirstPersonRendererOverrides;
+import net.minecraft.client.network.ClientPlayerEntity;
+import net.minecraft.client.render.VertexConsumerProvider;
+import net.minecraft.client.render.item.HeldItemRenderer;
+import net.minecraft.client.render.item.HeldItemRenderer.HandRenderType;
+import net.minecraft.client.util.math.MatrixStack;
+import net.minecraft.util.Arm;
+import net.minecraft.util.math.MathHelper;
+
+@Mixin(HeldItemRenderer.class)
+abstract class MixinHeldItemRenderer implements FirstPersonRendererOverrides.ArmRenderer {
+    @Shadow
+    private float equipProgressMainHand;
+    @Shadow
+    private float prevEquipProgressMainHand;
+
+    @Override
+    @Invoker("renderArmHoldingItem")
+    public abstract void invokeRenderArmHoldingItem(MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, float equipProgress, float swingProgress, Arm arm);
+
+    @Override
+    public float getEquipProgress(float tickDelta) {
+        return MathHelper.lerp(tickDelta, prevEquipProgressMainHand, equipProgressMainHand);
+    }
+
+    @Inject(
+        method = "getHandRenderType",
+        at = @At("HEAD"),
+        cancellable = true
+    )
+    private static void onGetHandRenderType(ClientPlayerEntity player, CallbackInfoReturnable<HandRenderType> info) {
+        FirstPersonRendererOverrides.INSTANCE.getHandRenderType(player).ifPresent(info::setReturnValue);
+    }
+
+    @Inject(
+        method = "renderItem(FLnet/minecraft/client/util/math/MatrixStack;Lnet/minecraft/client/render/VertexConsumerProvider$Immediate;Lnet/minecraft/client/network/ClientPlayerEntity;I)V",
+        at = @At(
+            value = "FIELD",
+            target = "net/minecraft/client/render/item/HeldItemRenderer$HandRenderType.renderMainHand",
+            shift = Shift.BEFORE
+        ),
+        cancellable = true)
+    private void onRenderItem(float tickDelta, MatrixStack matrices, VertexConsumerProvider.Immediate vertexConsumers, ClientPlayerEntity player, int light, CallbackInfo info) {
+        if (FirstPersonRendererOverrides.INSTANCE.beforeRenderHands(this, tickDelta, matrices, vertexConsumers, player, light)) {
+            info.cancel();
+        }
+    }
+}

src/main/java/com/minelittlepony/unicopia/mixin/client/MixinPlayerEntityRenderer.java

@@ -21,14 +21,17 @@ import net.minecraft.client.util.math.MatrixStack;
 import net.minecraft.util.Arm;
 
 @Mixin(PlayerEntityRenderer.class)
-abstract class MixinPlayerEntityRenderer extends LivingEntityRenderer<AbstractClientPlayerEntity, PlayerEntityModel<AbstractClientPlayerEntity>> {
+abstract class MixinPlayerEntityRenderer
+        extends LivingEntityRenderer<AbstractClientPlayerEntity, PlayerEntityModel<AbstractClientPlayerEntity>>
+        implements FeatureRoot<AbstractClientPlayerEntity, PlayerEntityModel<AbstractClientPlayerEntity>> {
     @Nullable
     private AccessoryFeatureRenderer<AbstractClientPlayerEntity, PlayerEntityModel<AbstractClientPlayerEntity>> accessories;
 
     MixinPlayerEntityRenderer() { super(null, null, 0); }
 
+    @Override
     @SuppressWarnings("unchecked")
-    private AccessoryFeatureRenderer<AbstractClientPlayerEntity, PlayerEntityModel<AbstractClientPlayerEntity>> getAccessories() {
+    public AccessoryFeatureRenderer<AbstractClientPlayerEntity, PlayerEntityModel<AbstractClientPlayerEntity>> getAccessories() {
         if (accessories == null) {
             accessories = features.stream()
                 .filter(a -> a instanceof FeatureRoot)

src/main/resources/unicopia.aw

@@ -1,3 +1,4 @@
 accessWidener       v1       named
 accessible          class    net/minecraft/client/render/RenderLayer$MultiPhaseParameters
 accessible          method   net/minecraft/client/render/RenderLayer     of     (Ljava/lang/String;Lnet/minecraft/client/render/VertexFormat;Lnet/minecraft/client/render/VertexFormat$DrawMode;IZZLnet/minecraft/client/render/RenderLayer$MultiPhaseParameters;)Lnet/minecraft/client/render/RenderLayer$MultiPhase;
+accessible          class    net/minecraft/client/render/item/HeldItemRenderer$HandRenderType

src/main/resources/unicopia.mixin.json

@@ -47,6 +47,7 @@
     "client.MixinCamera",
     "client.MixinEntityRenderDispatcher",
     "client.MixinGameRenderer",
+    "client.MixinHeldItemRenderer",
     "client.MixinInGameHud",
     "client.MixinInGameHud$HeartType",
     "client.MixinItem",