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

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

cbuffer Params : register(b0)
{
    float Speed;
    float Drag;

    float InitialVelocity;
    float Time;
    float OrientTowardsVelocity;
    float RadiusFromW;

    float LifeTime;
}

cbuffer IntParams : register(b1)
{
    int TriggerEmit;
    int TriggerReset;
    int CollectCycleIndex;
    int SetFx1To;
    int SetFx2To;
    int EmitMode;
    int IsAutoCount;
    int EmitVelocityFactor;
}

StructuredBuffer<Point> EmitPoints : t0;
RWStructuredBuffer<Particle> Particles : u0;
RWStructuredBuffer<Point> ResultPoints : u1;

#define W_KEEP_ORIGINAL 0
#define W_PARTICLE_AGE 1
#define W_PARTICLE_SPEED 2

[numthreads(64, 1, 1)] void main(uint3 i : SV_DispatchThreadID)
{
    uint newPointCount, pointStride;
    EmitPoints.GetDimensions(newPointCount, pointStride);

    uint maxParticleCount, pointStride2;
    Particles.GetDimensions(maxParticleCount, pointStride2);

    uint gi = i.x;
    if (gi >= maxParticleCount)
        return;

    if (TriggerReset > 0.5)
    {
        Particles[gi].BirthTime = NAN;
        Particles[gi].Position = NAN;
        ResultPoints[gi].Scale = NAN;
    }

    // Insert emit points
    int addIndex = 0;
    if (EmitMode == 0)
    {
        addIndex = (gi + CollectCycleIndex + maxParticleCount) % maxParticleCount;
    }
    else
    {
        int t = (gi + CollectCycleIndex / newPointCount) % maxParticleCount;
        int blockSize = maxParticleCount / newPointCount;
        int particleBlock = t / blockSize;
        int t2 = t - (particleBlock * blockSize);
        addIndex = t2 > 0 ? -1 : particleBlock;
    }

    if (TriggerEmit && addIndex >= 0 && addIndex < (int)newPointCount)
    {
        if (EmitMode != 0)
        {
            Particles[(gi - 1) % maxParticleCount].BirthTime = NAN;
            Particles[(gi - 1) % maxParticleCount].Radius = NAN;
        }

        Point emitPoint = EmitPoints[addIndex];

        Particles[gi].Position = emitPoint.Position;
        Particles[gi].Rotation = emitPoint.Rotation;

        Particles[gi].Radius = emitPoint.Scale.x * RadiusFromW;
        Particles[gi].BirthTime = Time;

        float emitVelocity = InitialVelocity * (EmitVelocityFactor == 0 ? 1 : (EmitVelocityFactor == 1 ? emitPoint.FX1 : emitPoint.FX2));

        Particles[gi].Velocity = qRotateVec3(float3(0, 0, 1), normalize(Particles[gi].Rotation)) * emitVelocity;

        // These will not change over lifetime...
        Particles[gi].Color = emitPoint.Color;
        ResultPoints[gi].Scale = emitPoint.Scale;
        ResultPoints[gi].FX1 = emitPoint.FX1;
        ResultPoints[gi].FX2 = emitPoint.FX2;
        ResultPoints[gi].Color = emitPoint.Color;
    }

    if (Particles[gi].BirthTime == NAN)
        return;

    float3 velocity = Particles[gi].Velocity;

    // drag step (frame-rate independent)
    // velocity *= (1 - Drag);
    velocity *= pow(1.0f - Drag, Speed); // improved version that better aligns
    Particles[gi].Velocity = velocity;

    // position step
    float3 pos = Particles[gi].Position;
    pos += velocity * Speed * 0.01;

    Particles[gi].Position = pos;

    float speed = length(velocity);
    if (speed > 0.0001)
    {
        float f = saturate(speed * OrientTowardsVelocity);
        Particles[gi].Rotation = qSlerp(Particles[gi].Rotation, qLookAt(velocity / speed, float3(0, 1, 0)), f);
    }

    // Copy result
    // Todo: This could by optimized by not copying color
    // ResultPoints[gi] = Particles[gi];
    ResultPoints[gi].Position = Particles[gi].Position;
    ResultPoints[gi].Rotation = Particles[gi].Rotation;
    ResultPoints[gi].Color = Particles[gi].Color;

    // Attempt with lerping to smooth position updates
    // ResultPoints[gi].position = lerp(Particles[gi].p.position, ResultPoints[gi].position, 0);
    // ResultPoints[gi].rotation = Particles[gi].p.rotation;
    // ResultPoints[gi].w = Particles[gi].p.w;
    float lifeTime = LifeTime < 0.0
                         ? (IsAutoCount ? 100000 : (float)(maxParticleCount / (newPointCount * 60.0)))
                         : LifeTime;

    float normalizedAge = (IsAutoCount && LifeTime < 0) ? 1 : (Time - Particles[gi].BirthTime) / lifeTime;
    bool tooOld = normalizedAge > 1;

    if (SetFx1To == W_PARTICLE_AGE)
    {
        ResultPoints[gi].FX1 = normalizedAge;
    }
    else if (SetFx1To == W_PARTICLE_SPEED)
    {
        ResultPoints[gi].FX1 = speed * 100;
    }

    if (SetFx2To == W_PARTICLE_AGE)
    {
        ResultPoints[gi].FX2 = normalizedAge;
    }
    else if (SetFx2To == W_PARTICLE_SPEED)
    {
        ResultPoints[gi].FX2 = speed * 100;
    }

    if (tooOld)
    {
        ResultPoints[gi].Scale = NAN;
    }
}