Hyprland/src/helpers/BezierCurve.cpp

#include "BezierCurve.hpp"

#include <algorithm>

void CBezierCurve::setup(std::vector<Vector2D>* pVec) {
    m_dPoints.clear();

    const auto BEGIN = std::chrono::high_resolution_clock::now();

    m_dPoints.emplace_back(Vector2D(0, 0));

    for (auto& p : *pVec) {
        m_dPoints.push_back(p);
    }

    m_dPoints.emplace_back(Vector2D(1, 1));

    RASSERT(m_dPoints.size() == 4, "CBezierCurve only supports cubic beziers! (points num: %i)", m_dPoints.size());

    // bake BAKEDPOINTS points for faster lookups
    // T -> X ( / BAKEDPOINTS )
    for (int i = 0; i < BAKEDPOINTS; ++i) {
        m_aPointsBaked[i] = Vector2D(getXForT((i + 1) / (float)BAKEDPOINTS), getYForT((i + 1) / (float)BAKEDPOINTS));
    }

    const auto ELAPSEDUS  = std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::high_resolution_clock::now() - BEGIN).count() / 1000.f;
    const auto POINTSSIZE = m_aPointsBaked.size() * sizeof(m_aPointsBaked[0]) / 1000.f;

    const auto BEGINCALC = std::chrono::high_resolution_clock::now();
    for (float i = 0.1f; i < 1.f; i += 0.1f)
        getYForPoint(i);
    const auto ELAPSEDCALCAVG = std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::high_resolution_clock::now() - BEGINCALC).count() / 1000.f / 10.f;

    Debug::log(LOG, "Created a bezier curve, baked %i points, mem usage: %.2fkB, time to bake: %.2fµs. Estimated average calc time: %.2fµs.", BAKEDPOINTS, POINTSSIZE, ELAPSEDUS,
               ELAPSEDCALCAVG);
}

float CBezierCurve::getYForT(float t) {
    return 3 * t * pow(1 - t, 2) * m_dPoints[1].y + 3 * pow(t, 2) * (1 - t) * m_dPoints[2].y + pow(t, 3);
}

float CBezierCurve::getXForT(float t) {
    return 3 * t * pow(1 - t, 2) * m_dPoints[1].x + 3 * pow(t, 2) * (1 - t) * m_dPoints[2].x + pow(t, 3);
}

// Todo: this probably can be done better and faster
float CBezierCurve::getYForPoint(float x) {
    if (x >= 1.0)
        return 1.0;

    // binary search for the range UPDOWN X
    int upperT = BAKEDPOINTS - 1;
    int lowerT = 0;
    int mid    = upperT / 2;

    while (std::abs(upperT - lowerT) > 1) {
        if (m_aPointsBaked[mid].x > x) {
            upperT = mid;
        } else {
            lowerT = mid;
        }

        mid = (upperT + lowerT) / 2;
    }

    // in the name of performance i shall make a hack
    const auto LOWERPOINT = &m_aPointsBaked[std::clamp(lowerT, 0, BAKEDPOINTS - 1)];
    const auto UPPERPOINT = &m_aPointsBaked[std::clamp(upperT, 0, BAKEDPOINTS - 1)];

    const auto PERCINDELTA = (x - LOWERPOINT->x) / (UPPERPOINT->x - LOWERPOINT->x);

    if (std::isnan(PERCINDELTA) || std::isinf(PERCINDELTA)) // can sometimes happen for VERY small x
        return 0.f;

    return LOWERPOINT->y + (UPPERPOINT->y - LOWERPOINT->y) * PERCINDELTA;
}