How to translate localPosition of TouchEvent to coordinates of the LineChart? (projection)

[hmumixaM]

I am working on the LineChart, and I wish to allow users to drag points freely in the chart so that they can perform analysis on it. Analysis includes drawing a line based on 2 points of selection and calculate the length of the line.

The LineTouchResponse of touchCallback only returns coordinates of curves with given x-coordinate, but I wish the point can be dragged freely even outside the curve.

My current approach is to get the coordinate that user pointing at, and setState to draw a new point there. I am able to get localPosition (the pixel coordinate of the phone) from FlTouchEvent.localPosition, but I cannot draw a new point with the pixel coordinate. So is there a method to translate the localPosition to chart coordinates?

[icefee]

A flexible solution, It's works for me

BoxConstraints provided by a LayoutBuilder wrapped outside the LineChart

Offset pixelToCoordinate(Offset offset, BoxConstraints constraints) {
    return Offset(
        minX + (maxX - minX) * (offset.dx - reservedSizeY) / (constraints.maxWidth - reservedSizeY),
        minY +
            (maxY - minY) *
                (constraints.maxHeight - offset.dy - reservedSizeX) /
                (constraints.maxHeight - reservedSizeX));
}

[imaNNeo]

We can provide a method to convert screen coordinates to chart coordinates and vice-versa. We have the function internally, but it is not exposed yet.

[JeffOlajos]

Having an exposed interface that would allow us to convert a chart x, y coordinate to a local or global offset as well as the ability to convert a mouse x, y to a chart axis x,y would be super helpful. One other item that would be super handy is if the BarTouchData touchCallback for a stacked bar had the index of the rodStackItem chosen. That way we could provide tooltips and/or feedback based on the item below the mouse in the stacked bar rather than on just the bar itself. Found no way of doing that short of figuring out the y of the mose position and comparing that in the yFrom and yTo of the items. Thats how I landed on this thread. That also goes for FlSpot. KNowing if the mouse is directly over the spot (on a line chart) would allow us to better manage tooltips. Right now the tooltip get involked when the mouse is over the x coordinate (y is ignored)

[TheOlajos]

We can provide a method to convert screen coordinates to chart coordinates and vice-versa. We have the function internally, but it is not exposed yet.

This would be very helpful if you can expose that method for the next release.

[Ingenious-App-Studios]

We can provide a method to convert screen coordinates to chart coordinates and vice-versa. We have the function internally, but it is not exposed yet.

When will this be released?