Implement playable Mac client and rendering validation

extension/src/water_motion.h

@@ -0,0 +1,24 @@
+#pragma once
+#include <algorithm>
+#include <cstdint>
+
+namespace mtgodot {
+// MapOutdoorWater: one shared vertical translation, alternating a random
+// 0..-15cm endpoint and zero, linearly interpolated over 1000..3000ms.
+struct WaterMotion {
+	uint64_t start_ms = 0, duration_ms = 300;
+	double begin = 0, end = 0, current = 0;
+	bool initialized = false;
+	double sample(uint64_t now, uint64_t next_duration, double next_depth_cm) {
+		if (!initialized) { start_ms = now; initialized = true; }
+		if (now - start_ms > duration_ms) {
+			begin = current;
+			end = end == 0 ? -std::clamp(next_depth_cm, 0.0, 15.0) * 0.01 : 0;
+			start_ms = now;
+			duration_ms = std::clamp<uint64_t>(next_duration, 1000, 3000);
+		}
+		current = begin + (end - begin) * double(now - start_ms) / double(duration_ms);
+		return current;
+	}
+};
+}