Fix edge sneaking when upside down

src/main/java/com/minelittlepony/unicopia/mixin/gravity/MixinPlayerEntity.java

@@ -0,0 +1,43 @@
+package com.minelittlepony.unicopia.mixin.gravity;
+
+import org.spongepowered.asm.mixin.*;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.ModifyArg;
+import org.spongepowered.asm.mixin.injection.ModifyVariable;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import com.minelittlepony.unicopia.entity.Equine;
+
+import net.minecraft.entity.MovementType;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.util.math.Vec3d;
+
+@Mixin(PlayerEntity.class)
+abstract class MixinPlayerEntity {
+    @ModifyVariable(method = "adjustMovementForSneaking", at = @At("HEAD"), argsOnly = true)
+    private Vec3d flipMovementForSneaking(Vec3d movement) {
+        if (this instanceof Equine.Container eq && eq.get().getPhysics().isGravityNegative()) {
+            return movement.multiply(1, -1, 1);
+        }
+        return movement;
+    }
+
+    @Inject(method = "adjustMovementForSneaking", at = @At("RETURN"), cancellable = true)
+    private void unflipMovementForSneaking(Vec3d movement, MovementType type, CallbackInfoReturnable<Vec3d> info) {
+        if (this instanceof Equine.Container eq && eq.get().getPhysics().isGravityNegative()) {
+            info.setReturnValue(info.getReturnValue().multiply(1, -1, 1));
+        }
+    }
+
+    @ModifyArg(method = { "adjustMovementForSneaking", "method_30263" }, at = @At(
+            value = "INVOKE",
+            target = "net/minecraft/util/math/Box.offset(DDD)Lnet/minecraft/util/math/Box;"),
+            index = 1)
+    private double invertStepHeight(double stepHeight) {
+        if (this instanceof Equine.Container eq && eq.get().getPhysics().isGravityNegative()) {
+            return -stepHeight;
+        }
+        return stepHeight;
+    }
+}

src/main/resources/unicopia.mixin.json

@@ -58,6 +58,7 @@
     "gravity.MixinLivingEntity",
     "gravity.MixinMobEntity",
     "gravity.MixinWorld",
+    "gravity.MixinPlayerEntity",
     "gravity.MixinPistonBlockEntity",
     "gravity.MixinServerWorld",
     "gravity.MixinServerPlayerEntity",