Laurens-Packages/Packages/com.unity.visualeffectgraph/Editor/Models/Blocks/Implementations/Velocity/VelocityTangent.cs

using System;
using System.Linq;
using System.Collections.Generic;
using UnityEngine;

namespace UnityEditor.VFX.Block
{
    class VelocityTangentVariantProvider : VariantProvider
    {
        public override IEnumerable<Variant> GetVariants()
        {
            foreach (var mode in Enum.GetValues(typeof(AttributeCompositionMode)).Cast<AttributeCompositionMode>())
            {
                // Skip the composition mode from main provider
                if (mode == AttributeCompositionMode.Overwrite)
                    continue;

                var composition = VFXBlockUtility.GetNameString(mode);

                yield return new Variant(
                    $"{composition} Tangential Velocity from Direction & Speed",
                    null,
                    typeof(VelocityTangent),
                    new[]
                    {
                        new KeyValuePair<string, object>("composition", mode),
                    });
            }
        }
    }

    class VelocityTangentProvider : VariantProvider
    {
        public override IEnumerable<Variant> GetVariants()
        {
                yield return new Variant(
                    "Set".Label().AppendLiteral("Velocity from Direction & Speed").AppendLabel("Tangent"),
                    VelocityBase.Category,
                    typeof(VelocityTangent),
                    new[]
                    {
                        new KeyValuePair<string, object>("composition", AttributeCompositionMode.Overwrite),
                    },
                    () => new VelocityTangentVariantProvider());
        }
    }

    [VFXInfo(experimental = true, variantProvider = typeof(VelocityTangentProvider))]
    class VelocityTangent : VelocityBase
    {
        public override string name => base.name.AppendLabel("Tangent");
        protected override bool altersDirection => true;

        public override IEnumerable<VFXAttributeInfo> attributes
        {
            get
            {
                foreach (var attribute in base.attributes)
                    yield return attribute;

                yield return new VFXAttributeInfo(VFXAttribute.Position, VFXAttributeMode.Read);
            }
        }

        public class InputProperties
        {
            [Tooltip("Sets the axis from which the velocity is calculated. Particles move away from this axis.")]
            public Line axis = Line.defaultValue;
        }

        protected override IEnumerable<VFXPropertyWithValue> inputProperties
        {
            get
            {
                foreach (var property in PropertiesFromType("InputProperties"))
                    yield return property;

                foreach (var property in base.inputProperties)
                    yield return property;
            }
        }

        public override IEnumerable<VFXNamedExpression> parameters
        {
            get
            {
                foreach (var param in base.parameters)
                {
                    if (param.name == "axis_end")
                        continue;

                    yield return param;
                }

                var start = base.parameters.First(o => o.name == "axis_start").exp;
                var end = base.parameters.First(o => o.name == "axis_end").exp;

                yield return new VFXNamedExpression(VFXOperatorUtility.Normalize(end - start), "normalizedDir");
            }
        }

        public override string source
        {
            get
            {
                string outSource = @"float3 dir = normalizedDir; // normalize(axis_end - axis_start);
float3 projPos = (dot(dir, position - axis_start) * dir) + axis_start;
float3 tangentDirection = cross(normalize(position - projPos), dir);
";
                outSource += speedComputeString + "\n";
                outSource += string.Format(directionFormatBlendSource, "tangentDirection") + "\n";
                outSource += string.Format(velocityComposeFormatString, "direction * speed");
                return outSource;
            }
        }
    }
}