CategoryAxisWithZoomAndPanModel - class based FloatLinearAxisModel

[andrey-ananiev]

I made a chart based on categories, but with the ability to change the scale and panning on the X axis.

Unfortunately, this method does not work as expected. When the maxViewExtent value is large, I observe strange behavior in the chart. When panning, it expands or contracts, the Y axis moves across the screen, and the X axis labels are cut off.

Next, I discovered that the same strange phenomena occur when panning the chart with FloatLinearAxisModel.
Is this a bug?

I would like to take part in improving your library. What do I need to do for this? I would also be grateful if you look at the CategoryAxisWithZoomAndPanModel class I created and give your comments?

import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.dp
import io.github.koalaplot.core.xygraph.AxisModel

/**
 * An axis that uses arbitrary category objects instead of numbers as its values. It is a discrete
 * axis.
 * @param T The data type of the axis values.
 * @param categories The objects that represent values on this axis. If objects are duplicated
 * as defined by their equals method, the behavior is undefined.
 */
public class CategoryAxisWithZoomAndPanModel<T>(
    private val categories: List<T>,
    private val minBarCount: Int = 4,
    private val maxBarCount: Int = 8,
    private val allowZooming: Boolean = true,
    private val allowPanning: Boolean = true,
) : AxisModel<T> {
    /**
     * Returns the offset of the provided string within this Category axis.
     *
     * @throws IllegalArgumentException if [point] is not a valid category.
     * @param point One of the categories for this axis.
     * @return The offset of the category along the axis, between 0 and 1
     */

    private var floatLinearAxisModel : FloatLinearAxisModel = let {
        require(maxBarCount >= minBarCount) {
            "maxBarCount must be greater than or equal to minBarCount"
        }
        val range = 0f.. categories.size.toFloat()
        val minViewExtent = minBarCount.toFloat().coerceIn(range)
        val maxViewExtent = maxBarCount.toFloat().coerceIn(range)
        FloatLinearAxisModel(
            range = range,
            minViewExtent = minViewExtent,
            maxViewExtent = maxViewExtent,
            minimumMajorTickSpacing = 1.dp,
            minimumMajorTickIncrement = 1f,
            minorTickCount = 1,
            allowZooming = allowZooming,
            allowPanning = allowPanning
        )
    }

    override fun computeOffset(point: T): Float {
        val index = categories.indexOf(point)
        require(index != -1) { "The provided category '$point' is not a valid value for this axis." }
        return floatLinearAxisModel.computeOffset(index + 0.5F)
    }

    override fun computeTickValues(axisLength: Dp): io.github.koalaplot.core.xygraph.TickValues<T> {
        return TickValues(categories, listOf())
    }

    override fun zoom(zoomFactor: Float, pivot: Float) {
        floatLinearAxisModel.zoom(zoomFactor, pivot)
    }

    override fun pan(amount: Float) {
        floatLinearAxisModel.pan(amount)
    }

    private data class TickValues<T>(override val majorTickValues: List<T>, override val minorTickValues: List<T>) :
        io.github.koalaplot.core.xygraph.TickValues<T>
}

[gsteckman]

Hi @andrey-ananiev, glad to hear you'd like to help out. Can you provide an example using FloatLinearAxisModel that I can run to see the behavior myself?

As far as making a zoom/pan capable version of the Category axis, I think delegating to the IntLinearAxisModel will likely produce better results than using FloatLinearAxisModel, due to rounding issues. Also try setting minorTickCount to 0.