Fix EntityPositionDeltaPacket format for 1.8.9; closes #190

minecraft/networking/packets/clientbound/play/__init__.py

@@ -5,7 +5,7 @@ from minecraft.networking.packets import (
 from minecraft.networking.types import (
     FixedPoint, Integer, Angle, UnsignedByte, Byte, Boolean, UUID, Short,
     VarInt, Double, Float, String, Enum, Difficulty, Long, Vector, Direction,
-    PositionAndLook, multi_attribute_alias,
+    PositionAndLook, multi_attribute_alias, attribute_transform,
 )
 
 from .combat_event_packet import CombatEventPacket
@@ -225,13 +225,29 @@ class EntityPositionDeltaPacket(Packet):
                0x15
 
     packet_name = "entity position delta"
-    get_definition = staticmethod(lambda context: [
-        {'entity_id': VarInt},
-        {'delta_x': Short},
-        {'delta_y': Short},
-        {'delta_z': Short},
-        {'on_ground': Boolean}
-    ])
+
+    @staticmethod
+    def get_definition(context):
+        delta_type = FixedPoint(Short, 12) \
+                     if context.protocol_version >= 106 else \
+                     FixedPoint(Byte)
+        return [
+            {'entity_id': VarInt},
+            {'delta_x_float': delta_type},
+            {'delta_y_float': delta_type},
+            {'delta_z_float': delta_type},
+            {'on_ground': Boolean},
+        ]
+
+    # The following transforms are retained for backward compatibility;
+    # they represent the delta values as fixed-point integers with 5 bits
+    # of fractional part, regardless of the protocol version.
+    delta_x = attribute_transform('delta_x_float', lambda x: int(x * 32),
+                                                   lambda x: x / 32)
+    delta_y = attribute_transform('delta_y_float', lambda y: int(y * 32),
+                                                   lambda y: y / 32)
+    delta_z = attribute_transform('delta_z_float', lambda z: int(z * 32),
+                                                   lambda z: z / 32)
 
 
 class TimeUpdatePacket(Packet):

minecraft/networking/types/utility.py

@@ -10,7 +10,7 @@ from itertools import chain
 __all__ = (
     'Vector', 'MutableRecord', 'Direction', 'PositionAndLook', 'descriptor',
     'overridable_descriptor', 'overridable_property', 'attribute_alias',
-    'multi_attribute_alias',
+    'multi_attribute_alias', 'attribute_transform',
 )
 
 
@@ -92,13 +92,20 @@ class MutableRecord(object):
                 yield slot
 
 
+def attribute_transform(name, from_orig, to_orig):
+    """An attribute descriptor that provides a view of a different attribute
+       with a given name via a given transformation and its given inverse."""
+    return property(
+        fget=(lambda self: from_orig(getattr(self, name))),
+        fset=(lambda self, value: setattr(self, name, to_orig(value))),
+        fdel=(lambda self: delattr(self, name)))
+
+
 def attribute_alias(name):
     """An attribute descriptor that redirects access to a different attribute
        with a given name.
     """
-    return property(fget=(lambda self: getattr(self, name)),
-                    fset=(lambda self, value: setattr(self, name, value)),
-                    fdel=(lambda self: delattr(self, name)))
+    return attribute_transform(name, lambda x: x, lambda x: x)
 
 
 def multi_attribute_alias(container, *arg_names, **kwd_names):

tests/test_backward_compatible.py

@@ -160,3 +160,15 @@ class ClassMemberAliasesTest(unittest.TestCase):
 
                 with self.assertRaises(AttributeError):
                     del packet.pure_game_mode
+
+    def test_entity_position_delta_packet(self):
+        packet = clientbound.play.EntityPositionDeltaPacket()
+        packet.delta_x = -128
+        packet.delta_y = 33
+        packet.delta_z = 127
+        self.assertEqual(packet.delta_x_float, -4.0)
+        self.assertEqual(packet.delta_y_float, 1.03125)
+        self.assertEqual(packet.delta_z_float, 3.96875)
+        self.assertEqual(packet.delta_x, -128)
+        self.assertEqual(packet.delta_y, 33)
+        self.assertEqual(packet.delta_z, 127)