Apply marker with more precision than whole chart.

[ployt0]

I have multiple data sets in one screen / chart host. One is a line of best fit which I've plotted at every X. I can thin it, but there is still the problem of it showing data near to the actual data set that I did not interpolate, and hence care more about displaying.

    CartesianChartHost(
        rememberCartesianChart(
            rememberLineCartesianLayer(
                LineCartesianLayer.LineProvider.series(
                    LineCartesianLayer.Line(
                        LineCartesianLayer.LineFill.single(fill(Color(0xffcc2b2b)))
                    )
                ),
            rememberLineCartesianLayer(
                LineCartesianLayer.LineProvider.series(
                    LineCartesianLayer.Line(
                        LineCartesianLayer.LineFill.single(fill(Color(0xff882beb)))
                    )
                ),
             ),
            marker = rememberMarker(
                // This is how we pop up details on touch... No composable allowed, maybe we can
                // edit the text... Author said to draw "on the `Canvas` using Vico or Android APIs"
                // https://github.com/patrykandpatrick/vico/discussions/648
                valueFormatter = DefaultCartesianMarker.ValueFormatter.default(),
            ),

It would be nice if marker was applicable below the chart level, at say the layer level.

[Gowsky]

Hello, @ployt0. First, you should most likely be using one LineCartesianLayer with two series, not two separate LineCartesianLayers with one series each.

Regarding the question, could you be more specific? What is the desired behavior vs. the current behavior? Would you like the marker to be connected to only one series?

To address the comment in the code, you can customize much more than the text — CartesianMarker gives you full flexibility. It's an interface that lets you draw anything at all on the Canvas. You can use both Vico APIs (TextComponent, LineComponent, etc.) and Android's built-in Canvas APIs to do so.

DefaultCartesianMarker is the default CartesianMarker implementation, which lets you build a baseline CartesianMarker by providing several components. DefaultCartesianMarker.ValueFormatter lets you customize the label of a marker created this way. DefaultCartesianMarker is quite flexible overall, but if you need more freedom, you can use the approach described above to implement any kind of marker.

It would be nice if marker was applicable below the chart level, at say the layer level.

It's applied at the chart level because that's what the user interacts with. Layers and line series with shared x values differ in z index, and that's not a dimension of touch input. However, you can still customize for what entries a marker is displayed.

[ployt0]

you should most likely be using one LineCartesianLayer with two series, not two separate LineCartesianLayers with one series each.

I don't see how I can make some series points, and another a line. The behaviour I require (points, line visibility) is defined in the rememberLineCartesianLayer/LineCartesianLayer parameter, lineProvider.

Correct me if I'm wrong, but that seems like your preference, architecturally. While I can't see it even working that way, I'm not able to express a preference for if I'd rather it did work that way.

Most of the rest of the stuff you mention, I believe I'd already figured out in the 4 days since posting. I believe the comment was a pointer for me to look at alternatives. Instead I just jumped around the code.

I know I can customize for what entries a marker is displayed, as I did 4 days ago. My point is that common marker parameter still sees data from all series, and despite my not displaying a label for it, the vertical line still sticks to it, making it more difficult for a user to horizontally align their touch with the scatter points, which I do label.

[Gowsky]

I don't see how I can make some series points, and another a line. The behaviour I require (points, line visibility) is defined in the rememberLineCartesianLayer/LineCartesianLayer parameter, lineProvider.

LineProvider is series-aware. This is its key feature. For example, if the first series is supposed to have points, and the second one is supposed to have a line, you'd do the following:

LineCartesianLayer.LineProvider.series(
    LineCartesianLayer.rememberLine(/* Point settings */),
    LineCartesianLayer.rememberLine(/* Line settings */),
)

Correct me if I'm wrong, but that seems like your preference, architecturally.

Using a single LineCartesianLayer for both series aligns with how the API was designed. It's faster and more memory-efficient. It also makes the code more concise.

despite my not displaying a label for it, the vertical line still sticks to it

There's a difference between not returning a label and not displaying the marker. I mentioned the latter. When you do so, the guideline won't be shown either. Markers are hidden via an early return from the drawing function.