Disable pitch and yaw rotations when rendering in first person mode

src/main/java/com/minelittlepony/api/model/RenderPass.java

@@ -0,0 +1,17 @@
+package com.minelittlepony.api.model;
+
+public enum RenderPass {
+    GUI,
+    WORLD,
+    HUD;
+
+    private static RenderPass CURRENT = WORLD;
+
+    public static RenderPass getCurrent() {
+        return CURRENT;
+    }
+
+    public static void swap(RenderPass pass) {
+        CURRENT = pass == null ? WORLD : pass;
+    }
+}

src/main/java/com/minelittlepony/client/mixin/MixinGameRenderer.java

@@ -0,0 +1,37 @@
+package com.minelittlepony.client.mixin;
+
+import net.minecraft.client.render.*;
+import net.minecraft.client.util.math.MatrixStack;
+
+import org.joml.Matrix4f;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import com.minelittlepony.api.model.RenderPass;
+
+@Mixin(GameRenderer.class)
+abstract class MixinGameRenderer {
+    @Inject(method = "renderWorld", at = @At("HEAD"))
+    private void beforeRenderWorld(float tickDelta, long limitTime, MatrixStack matrices, CallbackInfo info) {
+        RenderPass.swap(RenderPass.WORLD);
+    }
+
+    @Inject(method = "renderWorld", at = @At("RETURN"))
+    private void afterRenderWorld(float tickDelta, long limitTime, MatrixStack matrices, CallbackInfo info) {
+        RenderPass.swap(RenderPass.GUI);
+    }
+}
+
+@Mixin(value = WorldRenderer.class, priority = 0)
+abstract class MixinWorldRenderer {
+    @Inject(method = "render", at = @At(
+            value = "INVOKE",
+            target = "net.minecraft.client.render.VertexConsumerProvider$Immediate.drawCurrentLayer()V",
+            ordinal = 0
+    ))
+    private void onRender(MatrixStack matrices, float tickDelta, long limitTime, boolean renderBlockOutline, Camera camera, GameRenderer gameRenderer, LightmapTextureManager lightmapTextureManager, Matrix4f positionMatrix, CallbackInfo info) {
+        RenderPass.swap(RenderPass.HUD);
+    }
+}

src/main/java/com/minelittlepony/client/model/AbstractPonyModel.java

@@ -105,9 +105,7 @@ public abstract class AbstractPonyModel<T extends LivingEntity> extends ClientPo
         PonyModelPrepareCallback.EVENT.invoker().onPonyModelPrepared(entity, this, ModelAttributes.Mode.OTHER);
         super.setAngles(entity, move, swing, ticks, headYaw, headPitch);
 
-        head.pivotY = head.getDefaultTransform().pivotY;
-        head.pivotX = head.getDefaultTransform().pivotX;
-        head.pivotZ = head.getDefaultTransform().pivotZ;
+        head.setPivot(head.getDefaultTransform().pivotX, head.getDefaultTransform().pivotY, head.getDefaultTransform().pivotZ);
 
         setModelAngles(entity, move, swing, ticks, headYaw, headPitch);
 

src/main/java/com/minelittlepony/client/render/EquineRenderManager.java

@@ -162,12 +162,7 @@ public class EquineRenderManager<T extends LivingEntity, M extends EntityModel<T
     public void updateModel(T entity, ModelAttributes.Mode mode) {
         pony = renderer.getEntityPony(entity);
         playerModel.applyMetadata(pony.metadata());
-        updateForEntity(pony, entity);
 
-        getModel().updateLivingState(entity, pony, mode);
-    }
-
-    private void updateForEntity(IPony pony, Entity entity) {
         if (pony.hasMetadata() && entity instanceof RegistrationHandler && ((RegistrationHandler)entity).shouldUpdateRegistration(pony)) {
             entity.calculateDimensions();
 
@@ -179,6 +174,8 @@ public class EquineRenderManager<T extends LivingEntity, M extends EntityModel<T
             }
             PonyDataCallback.EVENT.invoker().onPonyDataAvailable((PlayerEntity)entity, pony.metadata(), pony.defaulted(), EnvType.CLIENT);
         }
+
+        getModel().updateLivingState(entity, pony, mode);
     }
 
     public IPony getPony(T entity) {

src/main/java/com/minelittlepony/client/transform/PonyPosture.java

@@ -5,6 +5,7 @@ import net.minecraft.entity.LivingEntity;
 import net.minecraft.entity.player.PlayerEntity;
 
 import com.minelittlepony.api.model.IModel;
+import com.minelittlepony.api.model.RenderPass;
 
 public interface PonyPosture<T extends LivingEntity> {
 
@@ -19,7 +20,7 @@ public interface PonyPosture<T extends LivingEntity> {
     }
 
     default void apply(T player, IModel model, MatrixStack stack, float yaw, float ticks, int invert) {
-        if (applies(player)) {
+        if (RenderPass.getCurrent() == RenderPass.WORLD && applies(player)) {
             double motionX = player.getX() - player.prevX;
             double motionY = player.isOnGround() ? 0 : player.getY() - player.prevY;
             double motionZ = player.getZ() - player.prevZ;

src/main/resources/minelp.mixin.json

@@ -15,6 +15,8 @@
         "MixinClientPlayerEntity",
         "MixinPlayerMoveC2SPacket",
         "MixinPlayerPositionLookS2CPacket",
-        "MixinVertextConsumers"
+        "MixinVertextConsumers",
+        "MixinGameRenderer",
+        "MixinWorldRenderer"
     ]
 }