tooll3--t3/Operators/Lib/Assets/shaders/particles/SurfaceForce.hlsl

#include "shared/hash-functions.hlsl"
#include "shared/noise-functions.hlsl"
#include "shared/point.hlsl"
#include "shared/quat-functions.hlsl"

cbuffer Params : register(b0)
{
    float4x4 TransformVolume;
    float4x4 InverseTransformVolume;

    float Amount;
    float Bounciness;
    float RandomizeBounce;
    float RandomizeReflection;

    float Attraction;
    float Repulsion;
    float SpeedFactor;
    float InvertVolumeFactor;

    float AttractionDecay;
}

cbuffer Params : register(b1)
{
    int VolumeShape;
}

RWStructuredBuffer<Particle> Particles : u0;

static const int VolumeSphere = 0;
static const int VolumeBox = 1;
static const int VolumePlane = 2;
static const int VolumeCylinder = 3;
static const int VolumeNoise = 4;

[numthreads(64, 1, 1)] void main(uint3 i : SV_DispatchThreadID)
{
    uint maxParticleCount, _;
    Particles.GetDimensions(maxParticleCount, _);
    int gi = i.x;
    if (gi >= maxParticleCount)
        return;

    if (isnan(Particles[gi].BirthTime))
        return;

    // return;
    if (isnan(TransformVolume._11) || TransformVolume._11 == 0)
    {
        return;
    }

    float3 pos = Particles[gi].Position;
    float4 rot = Particles[gi].Rotation;
    float3 velocity = Particles[gi].Velocity;
    float r = Particles[gi].Radius;

    float3 posInVolume = mul(float4(pos, 1), TransformVolume).xyz;
    float3 posInVolumeNext = mul(float4(pos + velocity * SpeedFactor * 0.01 * 2, 1), TransformVolume).xyz;

    float unitLength = 1 * r / 2;
    float3 rInVolume = length(mul(float4(unitLength.xxx, 0), TransformVolume));

    // float s = 1;
    float distance = 0;
    float distanceNext = 0;
    float3 surfaceN = 0;
    if (VolumeShape == VolumeSphere)
    {
        float rUnitSphere = 0.5;
        distance = length(posInVolume) - rUnitSphere;
        distanceNext = length(posInVolumeNext) - rUnitSphere;
        surfaceN = normalize(posInVolume);
        // s = smoothstep(1 + FallOff, 1, distance);
    }
    else if (VolumeShape == VolumeBox)
    {
        float3 t1 = abs(posInVolume);
        surfaceN = t1.x > t1.y ? (t1.x > t1.z ? float3(sign(posInVolume.x), 0, 0) : float3(0, 0, sign(posInVolume.z)))
                               : (t1.y > t1.z ? float3(0, sign(posInVolume.y), 0) : float3(0, 0, sign(posInVolume.z)));

        float r1 = length(abs(rInVolume * surfaceN)) * InvertVolumeFactor;

        float rUnitSphere = 0.5;
        distance = max(max(t1.x, t1.y), t1.z) - rUnitSphere - r1;

        float3 t2 = abs(posInVolumeNext);
        distanceNext = max(max(t2.x, t2.y), t2.z) - rUnitSphere - r1;
    }
    else if (VolumeShape == VolumePlane)
    {
        distance = posInVolume.y - r * InvertVolumeFactor;
        distanceNext = posInVolumeNext.y - r * InvertVolumeFactor;
        surfaceN = float3(0, 1, 0);
        // s = smoothstep(FallOff, 0, distance);
    }
    else if (VolumeShape == VolumeCylinder)
    {
        // Assuming the cylinder is aligned along the y-axis
        float rCylinder = 0.5;
        float heightCylinder = 1.0;

        float2 xyPos = posInVolume.xz;
        float2 xyPosNext = posInVolumeNext.xz;

        float distanceToCenter = length(xyPos);
        float distanceToCenterNext = length(xyPosNext);

        // Check if the particle is within the radius of the cylinder
        if (distanceToCenter <= rCylinder)
        {
            distance = abs(posInVolume.y) - heightCylinder * 0.5;
            distanceNext = abs(posInVolumeNext.y) - heightCylinder * 0.5;

            // Set the surface normal based on the cylinder's orientation
            surfaceN = float3(0, sign(posInVolume.y), 0);
        }
        else
        {
            // Particle is outside the cylinder, use the distance to the cylinder surface
            distance = distanceToCenter - rCylinder;
            distanceNext = distanceToCenterNext - rCylinder;

            // Set the surface normal based on the cylinder's orientation
            surfaceN = float3(xyPos.x, 0, xyPos.y);
            surfaceN.y = 0; // Ignore the y-component, as it's already handled above
            surfaceN = normalize(surfaceN);
        }
    }

    float3 force = 0;

    surfaceN *= InvertVolumeFactor;
    float3 surfaceInWorld = normalize(mul(float4(surfaceN, 0), InverseTransformVolume).xyz);
    // float3 surfaceInWorld = surfaceN;

    if (sign(distance * distanceNext) < 0 && distance * InvertVolumeFactor > 0)
    {
        float4 rand = hash41u(gi);
        velocity = reflect(velocity, surfaceInWorld + (RandomizeReflection * (rand.xyz - 0.5))) * Bounciness * (RandomizeBounce * (rand.z - 0.5) + 1);
    }
    else
    {
        if (distance * InvertVolumeFactor < 0)
        {
            force = surfaceInWorld * Repulsion;
        }
        else
        {
            force = -surfaceInWorld * Attraction / (1 + distance * AttractionDecay);
        }
        velocity += force * SpeedFactor;
    }

    if (!isnan(velocity.x) && !isnan(velocity.y) && !isnan(velocity.z))
    {
        Particles[gi].Velocity = lerp(Particles[gi].Velocity, velocity, Amount);
    }
}