How to get Bezier points from a curve

I am drawing a Bezier curve in Qt using the inbuilt Qt functions:

void OpacityCurveWidget::paintEvent(QPaintEvent* event) {    QPainter painter(this);    painter.fillRect(0, 0, width(), height(), Qt::white);    painter.setPen(Qt::blue);    QPainterPath path;    glm::vec2 startPoint(0, (1.0 - opacityCurve[0].opacity) * height()); // Invert y-coordinate    path.moveTo(startPoint.x, startPoint.y);    for (size_t i = 1; i < opacityCurve.size(); ++i) {        int x1 = static_cast<int>(opacityCurve[i - 1].position.x * width());        int x2 = static_cast<int>(opacityCurve[i].position.x * width());        int y1 = static_cast<int>((1.0 - opacityCurve[i - 1].position.y) * height()); // Invert y-coordinate        int y2 = static_cast<int>((1.0 - opacityCurve[i].position.y) * height());     // Invert y-coordinate        int cx1 = static_cast<int>(opacityCurve[i - 1].handle2.x * width());        int cy1 = static_cast<int>((1.0 - opacityCurve[i - 1].handle2.y) * height()); // Invert y-coordinate        int cx2 = static_cast<int>(opacityCurve[i].handle1.x * width());        int cy2 = static_cast<int>((1.0 - opacityCurve[i].handle1.y) * height()); // Invert y-coordinate        QPointF startPointF(startPoint.x, startPoint.y);        QPointF controlPoint1F(cx1, cy1);        QPointF controlPoint2F(cx2, cy2);        QPointF endPointF(x2, y2);        path.cubicTo(controlPoint1F, controlPoint2F, endPointF);

After drawing them, I am able to move points and their handles save the new points and handles (x,y) position data to a vector.

Based on that data, I try to get the curve y position at given x position:

float OpacityCurveWidget::getYPositionAtX(float x) const {    if (opacityCurve.size() < 2) {        return 0.0f;    }    // Find the segment of the Bezier curve that contains the given x-coordinate    size_t segmentIndex = 0;    while (segmentIndex < opacityCurve.size() - 1 && x > opacityCurve[segmentIndex + 1].position.x) {        segmentIndex++;    }    // Calculate t, the parameter for the cubic Bezier curve formula    float t = (x - opacityCurve[segmentIndex].position.x) /        (opacityCurve[segmentIndex + 1].position.x - opacityCurve[segmentIndex].position.x);    // Use the cubic Bezier formula to calculate the y-coordinate    float y = (1 - t) * (1 - t) * (1 - t) * opacityCurve[segmentIndex].position.y +        3 * (1 - t) * (1 - t) * t * opacityCurve[segmentIndex].handle2.y +        3 * (1 - t) * t * t * opacityCurve[segmentIndex + 1].handle1.y +        t * t * t * opacityCurve[segmentIndex + 1].position.y;    // Invert the y-coordinate    y = 1.0f - y;    // Return the y-coordinate without multiplying by height    return y;}

The issue I am facing is that when I move the x Position of the curve point handle that also affects the y position of curve points in the Qt graph, but in my calculation, moving of any handle point only in x direction does not affect the y position of the points.

This is the QT Curve.

When i move any handle in x direction it also affects the y Position of curve Points.

How can i calculate the Y Position at at X 0.5 when total X length is 0 - 1.0 ?