Allow for mounted ponies to translate riding ponies onto their mount's backs, and apply postures to them

src/main/java/com/minelittlepony/PonyRenderManager.java

@@ -4,6 +4,7 @@ import java.util.Map;
 
 import com.google.common.collect.Maps;
 import com.minelittlepony.mixin.MixinRenderManager;
+import com.minelittlepony.ducks.IRenderPony;
 import com.minelittlepony.hdskins.gui.EntityPonyModel;
 import com.minelittlepony.hdskins.gui.RenderPonyModel;
 import com.minelittlepony.model.player.PlayerModels;
@@ -12,9 +13,14 @@ import com.minelittlepony.render.player.RenderPonyPlayer;
 import com.minelittlepony.render.ponies.MobRenderers;
 import com.mumfrey.liteloader.util.ModUtilities;
 
+import javax.annotation.Nullable;
+
+import net.minecraft.client.Minecraft;
 import net.minecraft.client.renderer.entity.Render;
+import net.minecraft.client.renderer.entity.RenderLivingBase;
 import net.minecraft.client.renderer.entity.RenderManager;
 import net.minecraft.entity.Entity;
+import net.minecraft.entity.EntityLivingBase;
 
 /**
  * Render manager responsible for replacing and restoring entity renderers when the client settings change.
@@ -88,4 +94,16 @@ public class PonyRenderManager {
     public LevitatingItemRenderer getMagicRenderer() {
         return magicRenderer;
     }
+
+    @SuppressWarnings("unchecked")
+    @Nullable
+    public <T extends EntityLivingBase, R extends RenderLivingBase<T> & IRenderPony<T>> R getPonyRenderer(T entity) {
+        Render<Entity> renderer = Minecraft.getMinecraft().getRenderManager().getEntityRenderObject(entity);
+
+        if (renderer instanceof RenderLivingBase && renderer instanceof IRenderPony) {
+            return (R)(Object)renderer;
+        }
+
+        return null;
+    }
 }

src/main/java/com/minelittlepony/ducks/IRenderPony.java

@@ -2,7 +2,10 @@ package com.minelittlepony.ducks;
 
 import com.minelittlepony.model.ModelWrapper;
 import com.minelittlepony.pony.data.IPony;
+import com.minelittlepony.render.RenderPony;
+import com.minelittlepony.util.math.MathUtil;
 
+import net.minecraft.client.renderer.GlStateManager;
 import net.minecraft.entity.EntityLivingBase;
 
 /**
@@ -16,4 +19,19 @@ public interface IRenderPony<T extends EntityLivingBase> {
     ModelWrapper getModelWrapper();
 
     IPony getEntityPony(T entity);
+
+    RenderPony<T> getInternalRenderer();
+
+    /**
+     * Called by riders to have their transportation adjust their position.
+     */
+    default void translateRider(T entity, IPony entityPony, EntityLivingBase passenger, IPony passengerPony, float ticks) {
+        if (!passengerPony.getRace(false).isHuman()) {
+            float yaw = MathUtil.interpolateDegress(entity.prevRenderYawOffset, entity.renderYawOffset, ticks);
+
+            GlStateManager.translate(0, 0, 0.8F);
+
+            getInternalRenderer().applyPostureRiding(entity, entity.ticksExisted + ticks, yaw, ticks);
+        }
+    }
 }

src/main/java/com/minelittlepony/hdskins/gui/RenderPonyModel.java

@@ -111,4 +111,9 @@ public class RenderPonyModel extends RenderPlayerModel<EntityPonyModel> implemen
             }
         };
     }
+
+    @Override
+    public RenderPony<EntityPonyModel> getInternalRenderer() {
+        return renderPony;
+    }
 }

src/main/java/com/minelittlepony/render/RenderPony.java

@@ -1,5 +1,6 @@
 package com.minelittlepony.render;
 
+import com.minelittlepony.MineLittlePony;
 import com.minelittlepony.ducks.IRenderPony;
 import com.minelittlepony.model.AbstractPonyModel;
 import com.minelittlepony.model.ModelWrapper;
@@ -7,6 +8,7 @@ import com.minelittlepony.pony.data.IPony;
 import com.minelittlepony.transform.PonyPosture;
 
 import net.minecraft.client.renderer.GlStateManager;
+import net.minecraft.entity.Entity;
 import net.minecraft.entity.EntityLivingBase;
 
 public class RenderPony<T extends EntityLivingBase> {
@@ -41,6 +43,25 @@ public class RenderPony<T extends EntityLivingBase> {
         float s = getScaleFactor();
         GlStateManager.scale(s, s, s);
         enableModelRenderProfile();
+
+        if (entity.isRiding()) {
+            Entity ridingEntity = entity.getRidingEntity();
+
+            if (ridingEntity instanceof EntityLivingBase) {
+
+                IRenderPony<EntityLivingBase> renderer = MineLittlePony.getInstance().getRenderManager().getPonyRenderer((EntityLivingBase)ridingEntity);
+
+                if (renderer != null) {
+                    // negate vanilla translations so the rider begins at the ridees feet.
+                    GlStateManager.translate(0, entity.getYOffset() + ridingEntity.getMountedYOffset(), 0);
+
+                    @SuppressWarnings("unchecked")
+                    IPony riderPony = renderer.getEntityPony((EntityLivingBase)ridingEntity);
+
+                    renderer.translateRider((EntityLivingBase)ridingEntity, riderPony, entity, pony, ticks);
+                }
+            }
+        }
     }
 
     @SuppressWarnings("unchecked")
@@ -54,6 +75,18 @@ public class RenderPony<T extends EntityLivingBase> {
         }
     }
 
+    @SuppressWarnings("unchecked")
+    public void applyPostureRiding(T player, float pitch, float yaw, float ticks) {
+        PonyPosture<?> posture = getPosture(player);
+        if (posture != null && posture.applies(player)) {
+            double motionX = player.posX - player.prevPosX;
+            double motionY = player.onGround ? 0 : player.posY - player.prevPosY;
+            double motionZ = player.posZ - player.prevPosZ;
+
+            ((PonyPosture<EntityLivingBase>)posture).transform(ponyModel, player, motionX, -motionY, motionZ, pitch, yaw, ticks);
+        }
+    }
+
     private PonyPosture<?> getPosture(T entity) {
         if (entity.isElytraFlying()) {
             return PonyPosture.ELYTRA;

src/main/java/com/minelittlepony/render/RenderPonyMob.java

@@ -11,6 +11,7 @@ import com.minelittlepony.render.layer.LayerPonyArmor;
 import com.minelittlepony.render.layer.LayerPonyCustomHead;
 import com.minelittlepony.render.layer.LayerPonyElytra;
 import com.voxelmodpack.hdskins.HDSkinManager;
+
 import net.minecraft.client.renderer.GlStateManager;
 import net.minecraft.client.renderer.entity.RenderLiving;
 import net.minecraft.client.renderer.entity.RenderManager;
@@ -92,6 +93,11 @@ public abstract class RenderPonyMob<T extends EntityLiving> extends RenderLiving
         return HDSkinManager.INSTANCE.getConvertedSkin(getTexture(entity));
     }
 
+    @Override
+    public RenderPony<T> getInternalRenderer() {
+        return renderPony;
+    }
+
     protected abstract ResourceLocation getTexture(T entity);
 
     public abstract static class Proxy<T extends EntityLiving> extends RenderPonyMob<T> {

src/main/java/com/minelittlepony/render/player/RenderPonyPlayer.java

@@ -138,4 +138,8 @@ public class RenderPonyPlayer extends RenderPlayer implements IRenderPony<Abstra
         return MineLittlePony.getInstance().getManager().getPony(player);
     }
 
+    @Override
+    public RenderPony<AbstractClientPlayer> getInternalRenderer() {
+        return renderPony;
+    }
 }

src/main/java/com/minelittlepony/util/math/MathUtil.java

@@ -16,4 +16,13 @@ public class MathUtil {
 
         return angle;
     }
+
+    public static float interpolateDegress(float prev, float current, float partialTicks) {
+        float difference = current - prev;
+
+        while (difference < -180) difference += 360;
+        while (difference >= 180) difference -= 360;
+
+        return prev + partialTicks * difference;
+    }
 }