Expose an AxisItemPlacer.Horizontal implementation that allows manual filtering of values

[kevincianfarini]

I have a requirement in our graphing features to display X-axis labels for the times of the day. Specifically, I need to expose:

• 00:00
• 06:00
• 12:00
• 18:00
• 23:00

The interval spacing of these axis labels are not uniform, and therefore I can't use the default horizontal placer with a spacing of 1.

I'm thinking a dynamic API for this kind of thing would be very nice. Perhaps something like the following?

// Companion object in AxisItemPlacer.Horizontal
public companion object {
  
  fun dynamic(predicate: (xIndex: Float) -> Boolean) = DynamicHorizontalItemPlacer(...)
}

// usage
itemPlacer = AxisItemPlacer.Horizontal.dynamic { xIndex: Float
  xIndex.toInt() % 6 == 0 || xIndex.toInt() == 23
}

If there's an easier way to achieve this behavior without providing a fully custom implementation of AxisItemPlacer.Horizontal please let me know! I wasn't able to find a way to do so.

[patrickmichalik]

Hello! Thanks for the suggestion. This would certainly be a useful addition—we’ll look into it.

For the time being, to implement the behavior in question, you’ll have to create a custom AxisItemPlacer.Horizontal implementation. You could write it from scratch or use the DefaultHorizontalAxisItemPlacer definition as a starting point, copying it over and adding the required check.

[patrickmichalik]

The example is almost ready, @kevincianfarini. I had some unforseen things come up, which led to a slight delay, but I expect to finalize and share the code tomorrow. If Saturday is the last day of the week for you, this will be a bit later than originally predicted, hence the update. Thanks for your patience.

[kevincianfarini]

No worries! Thank you so much. There's no rush, I just wanted to make sure I didn't slip through the cracks 😄

[patrickmichalik]

Please find the code here, @kevincianfarini. I’ve made some modifications for better alignment with your chart and with the snippets that you’ve shared. A few comments:

1. This is compatible with Vico 2.0.0 Alpha 15 and later. Notably, the ability to create HorizontalAxis and VerticalAxis subclasses was added in Vico 2.0.0 Alpha 15. Previously, one had to copy the definitions.
2. BottomAxis handles only those HorizontalAxis features that your chart uses. BaseAxis#guideline, for example, is ignored.
3. The assumption is made that all labels will fit. I didn’t add any logic for overlap prevention, as I’m not familiar with what your requirements are in that respect.
4. labelPredicate has a CartesianDrawContext receiver type. This isn’t necessary for the example—I added it in case you need to access the CartesianChartModel from the lambda. This relates to the second paragraph here.

If you need any help adapting this for an older Vico version (point 1), adding support for an unhandled HorizontalAxis feature (point 2), or implementing overlap prevention (point 3), please let me know. I’ll also be happy to answer any other questions you may have.

[kevincianfarini]

Thank you so much!

[patrickmichalik]

You’re welcome!