howardjones/network-weathermap

<?php

namespace Weathermap\Core;

/**
 * Given 4 ordinates and a parameter from 0 to 1, calculate a point on the Catmull-Rom spline through them.
 */

class CatmullRom1D
{
    private $aParam;
    private $bParam;
    private $cParam;
    private $dParam;

    public function __construct($point0, $point1, $point2, $point3)
    {
        $this->aParam = -$point0 + 3 * $point1 - 3 * $point2 + $point3;
        $this->bParam = 2 * $point0 - 5 * $point1 + 4 * $point2 - $point3;
        $this->cParam = -$point0 + $point2;
        $this->dParam = 2 * $point1;
    }

    /**
     * Calculate the ordinate given the parameter (t)
     *
     * @param float $parameter
     * @return float
     */
    public function calculate($parameter)
    {
        $parameterSquared = $parameter * $parameter;
        $parameterCubed = $parameterSquared * $parameter;

        return (
                ($this->aParam * $parameterCubed)
                + ($this->bParam * $parameterSquared)
                + ($this->cParam * $parameter)
                + $this->dParam
            ) / 2;
    }
}