o3de-atom-sampleviewer/Shaders/VertexAnimation.azsl

/*
 * Copyright (c) Contributors to the Open 3D Engine Project.
 * For complete copyright and license terms please see the LICENSE at the root of this distribution.
 *
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 *
 */

#include <Atom/Features/SrgSemantics.azsli>
#include <Atom/RPI/Math.azsli>

ShaderResourceGroup PassSrg : SRG_PerPass
{
    StructuredBuffer<float3> m_sourceVertexData;
    RWStructuredBuffer<float3> m_targetVertexData;
    StructuredBuffer<float3> m_instanceOffsetData;
    float m_frameTime;
    uint m_vertexCountPerInstance;
    uint m_targetVertexStridePerInstance;
}

class ContinuousSineRng
{
    uint m_seed;
    float m_timeshift;

    void Initialize(float3 position, uint instanceIndex, float timeshift)
    {
        m_seed = 0;
        m_seed ^= asuint(position.x);
        Xorshift(m_seed);
        m_seed ^= asuint(position.y);
        Xorshift(m_seed);
        m_seed ^= asuint(position.z);
        Xorshift(m_seed);

        m_seed ^= instanceIndex;
        Xorshift(m_seed);

        m_timeshift = timeshift;
    }

    float GetRandomNormalizedFloat()
    {
        // Duration in seconds after which the animation repeats
        float animationDuration = (Xorshift(m_seed) % 60 + 120) / 60.f;

        // The float values passed to the sin-function should not be too large, otherwise the result is not continuous
        uint seedSmall = m_seed % 1024;
        float timeshiftSmall = (m_timeshift % animationDuration) / animationDuration * TWO_PI;
        return sin(seedSmall + timeshiftSmall) * 0.5f + 0.5f;
    }

    float3 GetRandomUnitSphereDirection()
    {
        float z = GetRandomNormalizedFloat() * 2.f - 1.f;
        float phi = GetRandomNormalizedFloat() * TWO_PI;

        float rxy = sqrt(1.f - z * z);
        float x = rxy * cos(phi);
        float y = rxy * sin(phi);

        return normalize(float3(x, y, z));
    }
};

[numthreads(64, 1, 1)]
void AnimateVertices(uint3 dispatchId : SV_DispatchThreadID)
{
    uint instanceIndex = dispatchId.x / PassSrg::m_vertexCountPerInstance;
    uint inputIndex = dispatchId.x % PassSrg::m_vertexCountPerInstance;
    uint outputIndex = instanceIndex * PassSrg::m_targetVertexStridePerInstance + inputIndex;

    ContinuousSineRng rng;
    rng.Initialize(PassSrg::m_sourceVertexData[inputIndex], instanceIndex, PassSrg::m_frameTime);

    // Animated the vertices by displacing each vertex in a random direction by a random amount
    float3 animationMoveDirection = rng.GetRandomUnitSphereDirection();
    float animationMoveAmount = rng.GetRandomNormalizedFloat() * 0.02f;

    // Need to move vertices per instance in the compute shader since CLAS does not have a separate transform
    float3 vertexBaseLocation = PassSrg::m_instanceOffsetData[instanceIndex] + PassSrg::m_sourceVertexData[inputIndex];

    PassSrg::m_targetVertexData[outputIndex] = vertexBaseLocation + animationMoveDirection * animationMoveAmount;
}