Monogame-Extended/source/MonoGame.Extended/Particles/Profiles/LineProfile.cs

// Copyright (c) Craftwork Games. All rights reserved.
// Licensed under the MIT license.
// See LICENSE file in the project root for full license information.

using System;
using Microsoft.Xna.Framework;

namespace MonoGame.Extended.Particles.Profiles;

/// <summary>
/// A profile that distributes particles uniformly along a line segment with random headings.
/// </summary>
/// <remarks>
/// The <see cref="LineProfile"/> positions particles randomly along a line segment centered at the emitter position and
/// defined by an axis direction and length.
/// </remarks>
public sealed class LineProfile : Profile
{
    /// <summary>
    /// The direction vector of the line axis.
    /// </summary>
    public Vector2 Axis;

    /// <summary>
    /// The length of the line segment.
    /// </summary>
    public float Length;

    /// <summary>
    /// The emission direction vector used when <see cref="Radiate"/> is <see cref="LineRadiation.Directional"/>
    /// or as a scale factor when <see cref="Radiate"/> is <see cref="LineRadiation.NormalUp"/> or <see cref="LineRadiation.NormalDown"/>.
    /// </summary>
    /// <remarks>
    /// For <see cref="LineRadiation.Directional"/>, this vector directly specifies the particle heading direction.
    /// For <see cref="LineRadiation.NormalUp"/> and <see cref="LineRadiation.NormalDown"/>, this vector's magnitude and sign
    /// control the normal emission behavior. Positive values emit in the specified normal direction, while negative values
    /// flip to the opposite direction.
    /// This property is ignored when <see cref="Radiate"/> is <see cref="LineRadiation.None"/>.
    /// </remarks>
    public Vector2 Direction = Vector2.UnitY;

    /// <summary>
    /// The radiation mode that determines how particle headings are calculated.
    /// </summary>
    public LineRadiation Radiate = LineRadiation.None;

    /// <summary>
    /// Computes the offset and heading for a new particle.
    /// </summary>
    /// <param name="offset">A pointer to the Vector2 where the offset from the emitter position will be stored.</param>
    /// <param name="heading">A pointer to the Vector2 where the unit direction vector will be stored.</param>
    /// <exception cref="InvalidOperationException">
    /// Thrown when <see cref="Radiate"/> contains an unsupported value.
    /// </exception>
    public override unsafe void GetOffsetAndHeading(Vector2* offset, Vector2* heading)
    {
        float value = FastRandom.Shared.NextSingle(Length * -0.5f, Length * 0.5f);
        offset->X = Axis.X * value;
        offset->Y = Axis.Y * value;

        // Calculate heading based on radiation mode
        switch (Radiate)
        {
            case LineRadiation.None:
                FastRandom.Shared.NextUnitVector(heading);
                break;

            case LineRadiation.Directional:
                Vector2 normalizedDirection = Vector2.Normalize(Direction);
                heading->X = normalizedDirection.X;
                heading->Y = normalizedDirection.Y;
                break;

            case LineRadiation.PerpendicularUp:
                Vector2 normalizedAxisUp = Vector2.Normalize(Axis);
                heading->X = normalizedAxisUp.Y;
                heading->Y = -normalizedAxisUp.X;
                break;

            case LineRadiation.PerpendicularDown:
                Vector2 normalizedAxisDown = Vector2.Normalize(Axis);
                heading->X = -normalizedAxisDown.Y;
                heading->Y = normalizedAxisDown.X;
                break;

            default:
                throw new InvalidOperationException($"Unsupported radiation mode '{Radiate}'");
        }
    }
}