feat: RechargeableDoubleComponent also has the value in percentage format as a binding

Author: AlmasB

fxgl/src/main/kotlin/com/almasb/fxgl/dsl/components/RechargeableComponents.kt

@@ -47,13 +47,18 @@ abstract class RechargeableDoubleComponent
 ) : DoubleComponent(initialValue) {
 
     private val maxValueProp = SimpleDoubleProperty(maxValue)
+    private val valuePercentBinding = valueProperty().divide(maxValueProp).multiply(100)
 
     fun maxValueProperty() = maxValueProp
+    fun valuePercentProperty() = valuePercentBinding
 
     var maxValue: Double
         get() = maxValueProp.value
         set(value) { maxValueProp.value = value }
 
+    val valuePercent: Double
+        get() = valuePercentBinding.value
+
     /**
      * Set component value to 0.
      */

fxgl/src/test/kotlin/com/almasb/fxgl/dsl/components/RechargeableDoubleComponentTest.kt

@@ -155,4 +155,16 @@ class RechargeableDoubleComponentTest {
         assertThat(value, `is`(30.0))
         assertThat(zero, `is`(false))
     }
+
+    @Test
+    fun `value in percent`() {
+        hp.value = 10.0
+        hp.maxValue = 100.0
+
+        assertThat(hp.valuePercent, `is`(10.0))
+
+        hp.maxValue = 50.0
+
+        assertThat(hp.valuePercent, `is`(20.0))
+    }
 }