Origin/Volume: Introduce support for custom origins and use in Volume

src/main/kotlin/graphics/scenery/Origin.kt

@@ -1,11 +1,14 @@
 package graphics.scenery
 
+import org.joml.Vector3f
+
 /**
  * Enum class to store origin information, e.g. for use with [graphics.scenery.volumes.Volume]s
  *
  * @author Ulrik Guenther <[email protected]>
  */
-enum class Origin {
-    Center,
-    FrontBottomLeft
+sealed class Origin {
+    object Center: Origin()
+    object FrontBottomLeft: Origin()
+    class Custom(val origin: Vector3f): Origin()
 }

src/main/kotlin/graphics/scenery/volumes/Volume.kt

@@ -166,7 +166,7 @@ open class Volume(
     }
 
     /** What to use as the volume's origin, scenery's default is [Origin.Center], BVV's default is [Origin.FrontBottomLeft]. **/
-    var origin = Origin.Center
+    var origin: Origin = Origin.Center
 
     /** Rendering method */
     var renderingMethod = RenderingMethod.AlphaBlending
@@ -1221,14 +1221,17 @@ open class Volume(
          * into account.
          */
         override fun composeModel() {
-            val shift = Vector3f(volume.getDimensions()) * (-0.5f)
-
             model.translation(position)
             model.mul(Matrix4f().set(this.rotation))
             model.scale(scale)
             model.scale(volume.localScale())
-            if (volume.origin == Origin.Center) {
-                model.translate(shift)
+            when(val o = volume.origin) {
+                is Origin.Center -> {
+                    val shift = Vector3f(volume.getDimensions()) * (-0.5f)
+                    model.translate(shift)
+                }
+                is Origin.Custom -> model.translate(o.origin)
+                else -> {}
             }
         }
     }