omath/source/projectile_prediction/ProjPredEngineLegacy.cpp

#include "omath/projectile_prediction/proj_pred_engine_legacy.hpp"
#include <cmath>
#include <omath/Angles.hpp>

namespace omath::projectile_prediction
{
    ProjPredEngineLegacy::ProjPredEngineLegacy(const float gravityConstant, const float simulationTimeStep,
                                               const float maximumSimulationTime, const float distanceTolerance) :
        m_gravityConstant(gravityConstant), m_simulationTimeStep(simulationTimeStep),
        m_maximumSimulationTime(maximumSimulationTime), m_distanceTolerance(distanceTolerance)
    {
    }

    std::optional<Vector3<float>> ProjPredEngineLegacy::MaybeCalculateAimPoint(const Projectile& projectile,
                                                                        const Target& target) const
    {
        for (float time = 0.f; time < m_maximumSimulationTime; time += m_simulationTimeStep)
        {
            const auto predictedTargetPosition = target.PredictPosition(time, m_gravityConstant);

            const auto projectilePitch = MaybeCalculateProjectileLaunchPitchAngle(projectile, predictedTargetPosition);

            if (!projectilePitch.has_value()) [[unlikely]]
                continue;

            if (!IsProjectileReachedTarget(predictedTargetPosition, projectile, projectilePitch.value(), time))
                continue;

            const auto delta2d = (predictedTargetPosition - projectile.m_origin).Length2D();
            const auto height = delta2d * std::tan(angles::DegreesToRadians(projectilePitch.value()));

            return Vector3(predictedTargetPosition.x, predictedTargetPosition.y, projectile.m_origin.z + height);
        }
        return std::nullopt;
    }

    std::optional<float>
    ProjPredEngineLegacy::MaybeCalculateProjectileLaunchPitchAngle(const Projectile& projectile,
                                                                   const Vector3<float>& targetPosition) const
    {
        const auto bulletGravity = m_gravityConstant * projectile.m_gravityScale;
        const auto delta = targetPosition - projectile.m_origin;

        const auto distance2d = delta.Length2D();
        const auto distance2dSqr = distance2d * distance2d;
        const auto launchSpeedSqr = projectile.m_launchSpeed * projectile.m_launchSpeed;

        float root = launchSpeedSqr * launchSpeedSqr -
                     bulletGravity * (bulletGravity * distance2dSqr + 2.0f * delta.z * launchSpeedSqr);

        if (root < 0.0f) [[unlikely]]
            return std::nullopt;

        root = std::sqrt(root);
        const float angle = std::atan((launchSpeedSqr - root) / (bulletGravity * distance2d));

        return angles::RadiansToDegrees(angle);
    }

    bool ProjPredEngineLegacy::IsProjectileReachedTarget(const Vector3<float>& targetPosition, const Projectile& projectile,
                                                         const float pitch, const float time) const
    {
        const auto yaw = projectile.m_origin.ViewAngleTo(targetPosition).y;
        const auto projectilePosition = projectile.PredictPosition(pitch, yaw, time, m_gravityConstant);

        return projectilePosition.DistTo(targetPosition) <= m_distanceTolerance;
    }
} // namespace omath::projectile_prediction