I allowed myself to use image from other stackoverflow's question. I hope that's fine
So using using functions of Path class (https://api.flutter.dev/flutter/dart-ui/Path-class.html) we can draw picture above
path.moveTo(startPoint.x, startPoint.y)
path.quadraticBezierTo(handlePoint.x, handlePoint.y, endPoint.x, endPoint.y)
My question is how I can calculate x,y of the highest point on drawn line ?
Use any ui softwares like Photoshop. Create a canvas of same size that you are planning to use while drawing this path in flutter. Now use a pen tool and draw a curve. Now you should get a handle on each point. By handle i mean a line that denotes the direction and length of curve. Check the right side handles position in the canvas using ruler (ctrl+ r) that's the top most point you are looking for.. also there are a few online tools available to convert svg to path if you are looking for an easy alternative
SOLUTION
ok So I went for PathMetric class, this is what is needed to find solution without finding the right mathematical formula.
List<PathMetric> metric = path.computeMetrics().toList();
PathMetric pathMetric = metric[0];
double lastPoint = size.height / 2;
double rightTangentOffset = 0;
for (double i = 0; i < pathMetric.length; i = i + 1) {
if (pathMetric.getTangentForOffset(i).position.dy < lastPoint) { // only for up parabola
lastPoint = pathMetric.getTangentForOffset(i).position.dy;
rightTangentOffset = i;
}
}
Offset position = pathMetric.getTangentForOffset(rightTangentOffset).position;
canvas.drawCircle(position, circleSize, circleOnLine);
you get an idea... lastPoint is due to where I start drawing.