TopCurvedEdgeTreatment.kt

import com.google.android.material.shape.EdgeTreatment
import com.google.android.material.shape.ShapePath

class TopCurvedEdgeTreatment(
    var fabCradleMargin: Float,
    var fabCradleRoundedCornerRadius: Float,
    var cradleVerticalOffset: Float
) : EdgeTreatment() {

    var fabDiameter: Float = 0F
    var horizontalOffset: Float = 0F

    init {
        if (cradleVerticalOffset < 0.0f) {
            throw IllegalArgumentException("cradleVerticalOffset must be positive.")
        } else {
            this.horizontalOffset = 0.0f
        }
    }

    override fun getEdgePath(length: Float, interpolation: Float, shapePath: ShapePath) {
        if (this.fabDiameter == 0.0f) {
            shapePath.lineTo(length, 0.0f)
        } else {
            val cradleDiameter = this.fabCradleMargin * 2.0f + this.fabDiameter
            val cradleRadius = cradleDiameter / 2.0f
            val roundedCornerOffset = interpolation * this.fabCradleRoundedCornerRadius
            val middle = length / 2.0f + this.horizontalOffset
            val verticalOffset = interpolation * this.cradleVerticalOffset + (1.0f - interpolation) * cradleRadius
            val verticalOffsetRatio = verticalOffset / cradleRadius
            if (verticalOffsetRatio >= 1.0f) {
                shapePath.lineTo(length, 0.0f)
            } else {
                val distanceBetweenCenters = cradleRadius + roundedCornerOffset
                val distanceBetweenCentersSquared = distanceBetweenCenters * distanceBetweenCenters
                val distanceY = verticalOffset + roundedCornerOffset
                val distanceX = Math.sqrt((distanceBetweenCentersSquared - distanceY * distanceY).toDouble()).toFloat()
                val leftRoundedCornerCircleX = middle - distanceX
                val rightRoundedCornerCircleX = middle + distanceX
                val cornerRadiusArcLength = Math.toDegrees(Math.atan((distanceX / distanceY).toDouble())).toFloat()
                val cutoutArcOffset = 90.0f - cornerRadiusArcLength
                shapePath.lineTo(leftRoundedCornerCircleX - roundedCornerOffset, 0.0f)
                shapePath.addArc(
                    leftRoundedCornerCircleX - roundedCornerOffset,
                    0.0f,
                    leftRoundedCornerCircleX + roundedCornerOffset,
                    roundedCornerOffset * 2.0f,
                    270.0f,
                    cornerRadiusArcLength
                )
                shapePath.addArc(
                    middle - cradleRadius,
                    -cradleRadius - verticalOffset,
                    middle + cradleRadius,
                    cradleRadius - verticalOffset,
                    180.0f - cutoutArcOffset,
                    cutoutArcOffset * 2.0f - 180.0f
                )
                shapePath.addArc(
                    rightRoundedCornerCircleX - roundedCornerOffset,
                    0.0f,
                    rightRoundedCornerCircleX + roundedCornerOffset,
                    roundedCornerOffset * 2.0f,
                    270.0f - cornerRadiusArcLength,
                    cornerRadiusArcLength
                )
                shapePath.lineTo(length, 0.0f)
            }
        }
    }

}