feat: establish android particle field rendering loop

tools/generate_particle_fixture_f32.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+"""Generate deterministic v1 little-endian OfflineFixture field payloads."""
+
+from pathlib import Path
+import struct
+
+
+GRID = 16
+ROOT = Path(__file__).resolve().parents[1] / "particle-fixtures"
+
+
+def velocity(fixture: str, x: int, y: int) -> tuple[float, float]:
+    if fixture == "uniform-east":
+        return 1.0, 0.0
+    if fixture == "uniform-north":
+        return 0.0, 1.0
+    local_x = (x + 0.5) / GRID - 0.5
+    local_y = (y + 0.5) / GRID - 0.5
+    return -2.0 * local_y, 2.0 * local_x
+
+
+for fixture in ("uniform-east", "uniform-north", "vortex"):
+    payload = bytearray()
+    for y in range(GRID):
+        for x in range(GRID):
+            payload.extend(struct.pack("<ff", *velocity(fixture, x, y)))
+    (ROOT / fixture / "field.f32").write_bytes(payload)