AspectRatio

package org.geepawhill.contentment.geometry

import javafx.beans.property.SimpleDoubleProperty
import tornadofx.*

class AspectRatio {
    val widthToHeightProperty = SimpleDoubleProperty(16.0 / 9.0)
    var widthToHeight by widthToHeightProperty

    val hostWidthProperty = SimpleDoubleProperty(0.0)
    var hostWidth by hostWidthProperty

    val hostHeightProperty = SimpleDoubleProperty(0.0)
    var hostHeight by hostHeightProperty

    val widthProperty = SimpleDoubleProperty(0.0)
    var width by widthProperty

    val heightProperty = SimpleDoubleProperty(0.0)
    var height by heightProperty

    val xProperty = SimpleDoubleProperty(0.0)
    var x by xProperty

    val yProperty = SimpleDoubleProperty(0.0)
    var y by yProperty

    init {
        hostWidthProperty.addListener { _ -> recalculate() }
        hostHeightProperty.addListener { _ -> recalculate() }
        widthToHeightProperty.addListener { _ -> recalculate() }
    }

    private fun recalculate() {
        val impliedHeightForWidth = (1.0 / widthToHeight) * hostWidth
        if (impliedHeightForWidth < hostHeight) {
            width = hostWidth
            height = impliedHeightForWidth
        } else {
            val impliedWidthForHeight = widthToHeight * hostHeight
            width = impliedWidthForHeight
            height = hostHeight
        }
        x = (hostWidth - width) / 2.0
        y = (hostHeight - height) / 2.0
    }
}

AspectRatioTest

package org.geepawhill.contentment.geometry

import org.assertj.core.api.Assertions.assertThat
import org.assertj.core.data.Percentage
import org.junit.jupiter.api.Test

class AspectRatioTest {

    private val ratio = AspectRatio()

    @Test
    fun `defaults to 16 x 9`() {
        assertThat(ratio.widthToHeight).isCloseTo(16.0 / 9.0, Percentage.withPercentage(0.01))
    }

    @Test
    fun `exact dimension match`() {
        ratio.hostWidth = 1600.0
        ratio.hostHeight = 900.0
        assertThat(ratio.width).isCloseTo(1600.0, Percentage.withPercentage(0.01))
        assertThat(ratio.height).isCloseTo(900.0, Percentage.withPercentage(0.01))
    }

    @Test
    fun `smaller dimension match`() {
        ratio.hostWidth = 1280.0
        ratio.hostHeight = 720.0
        assertThat(ratio.width).isCloseTo(1280.0, Percentage.withPercentage(0.01))
        assertThat(ratio.height).isCloseTo(720.0, Percentage.withPercentage(0.01))
    }

    @Test
    fun `larger dimension match`() {
        ratio.hostWidth = 1920.0
        ratio.hostHeight = 1080.0
        assertThat(ratio.width).isCloseTo(1920.0, Percentage.withPercentage(0.01))
        assertThat(ratio.height).isCloseTo(1080.0, Percentage.withPercentage(0.01))
    }

    @Test
    fun `not enough width`() {
        ratio.hostWidth = 1600.0
        ratio.hostHeight = 1080.0
        assertThat(ratio.width).isCloseTo(1600.0, Percentage.withPercentage(0.01))
        assertThat(ratio.height).isCloseTo(900.0, Percentage.withPercentage(0.01))
        assertThat(ratio.y).isCloseTo(90.0, Percentage.withPercentage(0.01))
        assertThat(ratio.x).isCloseTo(0.0, Percentage.withPercentage(0.01))
    }

    @Test
    fun `not enough height`() {
        ratio.hostWidth = 1920.0
        ratio.hostHeight = 720.0
        assertThat(ratio.width).isCloseTo(1280.0, Percentage.withPercentage(0.01))
        assertThat(ratio.height).isCloseTo(720.0, Percentage.withPercentage(0.01))
        assertThat(ratio.y).isCloseTo(0.0, Percentage.withPercentage(0.01))
        assertThat(ratio.x).isCloseTo(320.0, Percentage.withPercentage(0.01))
    }

    @Test
    fun `ratio change`() {
        ratio.hostWidth = 1600.0
        ratio.hostHeight = 1200.0
        assertThat(ratio.height).isCloseTo(900.0, Percentage.withPercentage(0.01))
        ratio.widthToHeight = 4.0 / 3.0
        assertThat(ratio.width).isCloseTo(1600.0, Percentage.withPercentage(0.01))
        assertThat(ratio.height).isCloseTo(1200.0, Percentage.withPercentage(0.01))
    }

}