Scripting in the Water System

You can add buoyancy to the water simulation with a script that queries the height of the water surface.

To do this, enable Script Interactions in the Water section of the HDRP Asset and in the Inspector for the water surface you want to query (see Settings and properties related to the Water System).

The WaterSearchParameters struct makes water height queries possible.

One object

This is an example script to float one object on a water surface.

using UnityEngine;
using UnityEngine.Rendering.HighDefinition;

public class FitToWaterSurface : MonoBehaviour
{
    public WaterSurface targetSurface = null;

    // Internal search params
    WaterSearchParameters searchParameters = new WaterSearchParameters();
    WaterSearchResult searchResult = new WaterSearchResult();

    // Update is called once per frame
    void Update()
    {
        if (targetSurface != null)
        {
            // Build the search parameters
            searchParameters.startPositionWS = searchResult.candidateLocationWS;
            searchParameters.targetPositionWS = gameObject.transform.position;
            searchParameters.error = 0.01f;
            searchParameters.maxIterations = 8;

            // Do the search
            if (targetSurface.ProjectPointOnWaterSurface(searchParameters, out searchResult))
            {
                Debug.Log(searchResult.projectedPositionWS);
                gameObject.transform.position = searchResult.projectedPositionWS;
            }
            else Debug.LogError("Can't Find Projected Position");
        }
    }
}

Multiple objects (with Burst)

This is an example script to float an array of objects on a water surface using the Burst compiler.

public class FitToWaterSurface_Burst : MonoBehaviour
    {
        // Public parameters
        public int resolution = 50;
        public WaterSurface waterSurface = null;

        // List of internal cubes
        List<GameObject> cubes = new List<GameObject>();

        // Input job parameters
        NativeArray<float3> targetPositionBuffer;

        // Output job parameters
        NativeArray<float> errorBuffer;
        NativeArray<float3> candidatePositionBuffer;
        NativeArray<float3> projectedPositionWSBuffer;
        NativeArray<float3> directionBuffer;
        NativeArray<int> stepCountBuffer;

        // Start is called before the first frame update
        void Start()
        {
            // Allocate the buffers
            targetPositionBuffer = new NativeArray<float3>(resolution * resolution, Allocator.Persistent);
            errorBuffer = new NativeArray<float>(resolution * resolution, Allocator.Persistent);
            candidatePositionBuffer = new NativeArray<float3>(resolution * resolution, Allocator.Persistent);
            projectedPositionWSBuffer = new NativeArray<float3>(count, Allocator.Persistent);
            directionBuffer = new NativeArray<float3>(count, Allocator.Persistent);
            stepCountBuffer = new NativeArray<int>(resolution * resolution, Allocator.Persistent);

            for (int y = 0; y < resolution; ++y)
            {
                for (int x = 0; x < resolution; ++x)
                {
                    GameObject newCube = GameObject.CreatePrimitive(PrimitiveType.Cube);
                    newCube.transform.parent = this.transform;
                    newCube.transform.localPosition = new Vector3(x * 5, 0.0f, y * 5);
                    cubes.Add(newCube);
                }
            }
        }

        // Update is called once per frame
        void Update()
        {
            if (waterSurface == null)
                return;
            // Try to get the simulation data if available
            WaterSimSearchData simData = new WaterSimSearchData();
            if (!waterSurface.FillWaterSearchData(ref simData))
                return;

            // Fill the input positions
            int numElements = resolution * resolution;
            for (int i = 0; i < numElements; ++i)
                targetPositionBuffer[i] = cubes[i].transform.position;

            // Prepare the first band
            WaterSimulationSearchJob searchJob = new WaterSimulationSearchJob();

            // Assign the simulation data
            searchJob.simSearchData = simData;

            // Fill the input data
            searchJob.targetPositionWSBuffer = targetPositionBuffer;
            searchJob.startPositionWSBuffer = targetPositionBuffer;
            searchJob.maxIterations = 8;
            searchJob.error = 0.01f;
            searchJob.includeDeformation = true;
            searchJob.excludeSimulation = false;

            searchJob.errorBuffer = errorBuffer;
            searchJob.candidateLocationWSBuffer = candidatePositionBuffer;
            searchJob.projectedPositionWSBuffer = projectedPositionWSBuffer;
            searchJob.directionBuffer = directionBuffer;
            searchJob.stepCountBuffer = stepCountBuffer;

            // Schedule the job with one Execute per index in the results array and only 1 item per processing batch
            JobHandle handle = searchJob.Schedule(numElements, 1);
            handle.Complete();

            // Fill the input positions
            for (int i = 0; i < numElements; ++i)
                cubes[i].transform.position = projectedPositionWSBuffer[i];
        }

        private void OnDestroy()
        {
            targetPositionBuffer.Dispose();
            errorBuffer.Dispose();
            candidatePositionBuffer.Dispose();
            projectedPositionWSBuffer.Dispose();
            directionBuffer.Dispose();
            stepCountBuffer.Dispose();
        }
    }

Limitations

Masks do not affect CPU simulations. As a result, buoyancy scripts produce incorrect results for masked water surfaces.