add dora-joy node publishing gamepad axes and buttons

dora_joy/message.py

@@ -0,0 +1,43 @@
+"""The wire shape of a `joy` message.
+
+dora 1.0 has no standard joystick type, so this schema is the whole contract a
+consumer gets. It is **declared, never inferred**: pyarrow reads an empty
+`axes` list as `list<null>`, which would mean the port silently changed type the
+moment somebody unplugged the pad.
+
+It is not `sensor_msgs/Joy`. There is no header, because dora already knows when
+a message arrived and a second clock in the payload only invites skew questions;
+buttons are booleans rather than ROS's `int32`, because a button is down or it is
+not; and `present` is a field rather than an absence of messages, because a
+consumer stopping a robot needs to tell "the pad is centred" from "the pad is
+gone" within a tick rather than within a timeout.
+"""
+
+import pyarrow as pa
+
+from dora_joy.gamepad import Sample
+
+JOY = pa.struct(
+    [
+        # Raw, exactly as SDL reports it: no deadzone, no expo, no rescaling.
+        # Shaping is a decision about what the pad means, which belongs to
+        # whoever is driving something with it.
+        ("axes", pa.list_(pa.float32())),
+        ("buttons", pa.list_(pa.bool_())),
+        ("present", pa.bool_()),
+    ]
+)
+
+
+def pack(sample: Sample) -> pa.Array:
+    """Build one `joy` message from a reading."""
+    return pa.array(
+        [
+            {
+                "axes": [float(value) for value in sample.axes],
+                "buttons": [bool(down) for down in sample.buttons],
+                "present": sample.present,
+            }
+        ],
+        type=JOY,
+    )