How to get y Position from a cubic bezeir curve

[summit]

I am drawing a bezeir curve in QT using Painter.

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);

            // Draw control points
            painter.setPen(Qt::black);
            painter.setBrush(Qt::green);  // Use a different color for control points
            painter.drawEllipse(controlPoint1F, 5, 5);
            painter.drawEllipse(controlPoint2F, 5, 5);

            // Draw lines connecting control points to curve points
            painter.setPen(Qt::darkGray);  // Choose a color for the connecting lines
            painter.drawLine(startPointF, controlPoint1F);
            painter.drawLine(endPointF, controlPoint2F);

            // Update startPoint for the next iteration
            startPoint = glm::vec2(x2, y2);
        }

        // Set the alpha value to 128 for semi-transparency (adjust as needed)
        QColor fillColor(0, 0, 255, 64); // Blue color with alpha = 128
        painter.setBrush(fillColor);
        painter.drawPath(path);

Now if i want to know the Y position of the curve at given time 0.5 how can i do that ?

[Chris Kawa]

See QPainterPath::pointAtPercent().

[summit]

@Chris-Kawa Thank you very much , this is what i needed.