removeChildAt in O(n) instead of O(n^2) and simplify removeChild (#2319)

Author: reosfire

korge/src/korlibs/korge/view/Container.kt

@@ -177,13 +177,29 @@ open class Container(
     @KorgeUntested
     fun getChildByName(name: String): View? = __children.firstOrNull { it.name == name }
 
-    fun removeChildAt(index: Int): Boolean =
-        removeChild(getChildAtOrNull(index))
+    fun removeChildAt(index: Int) = removeChildAt(index, 1) == 1
+
+    fun removeChildAt(index: Int, count: Int): Int {
+        if (count <= 0 || index < 0) return 0
+        val from = index
+        val to = minOf(index + count, numChildren)
+
+        for (removedIndex in from until to) {
+            val view = getChildAt(removedIndex)
+            view.parent = null
+            view.index = -1
+        }
+
+        __children.removeRange(from, to)
+
+        for (i in index until numChildren)
+            __children[i].index = i
 
-    // @TODO: Optimize
-    fun removeChildAt(index: Int, count: Int) {
-        repeat(count) { removeChildAt(index) }
         invalidateZIndexChildren()
+        invalidateContainer()
+        invalidateLocalBounds()
+
+        return to - from
     }
 
     // @TODO: Optimize
@@ -425,14 +441,17 @@ open class Container(
 
         view.parent?.invalidateZIndexChildren()
         view.removeFromParent()
+
         val aindex = index.clamp(0, this.numChildren)
-        view.index = aindex
         val children = __children
         children.add(aindex, view)
-        for (n in aindex + 1 until children.size) children[n].index = n // Update other indices
+        for (n in aindex until numChildren) children[n].index = n // Update other indices
+
         view.parent = this
         view.invalidate()
+
         onChildAdded(view)
+
         invalidateZIndexChildren()
         invalidateContainer()
         invalidateLocalBounds()
@@ -447,16 +466,9 @@ open class Container(
      * Remarks: If the parent of [view] is not this container, this function doesn't do anything.
      */
     fun removeChild(view: View?): Boolean {
-        //if (view == null) return false
         if (view?.parent !== this) return false
-        for (i in view.index + 1 until numChildren) __children[i].index--
-        __children.removeAt(view.index)
-        view.parent = null
-        view.index = -1
-        invalidateZIndexChildren()
-        invalidateContainer()
-        invalidateLocalBounds()
-        return true
+
+        return removeChildAt(view.index)
     }
 
     /**

korge/test/korlibs/korge/view/ContainerTest.kt

@@ -85,8 +85,33 @@ internal class ContainerTest {
             solidRect(1, 1).name("d")
             solidRect(1, 1).name("e")
         }
-        c.removeChildAt(1, 2)
+
+        val removedCount = c.removeChildAt(1, 2)
+
+        assertEquals(removedCount, 2)
+
         assertEquals(listOf("a", "d", "e"), c.children.map { it.name })
+
+        // Assert that the indices are correct
+        for (i in 0 until c.numChildren) {
+            assertEquals(i, c.children[i].index)
+        }
+    }
+
+    @Test
+    fun testRemoveMoreThanPresent() {
+        val c = Container().apply {
+            solidRect(1, 1).name("a")
+            solidRect(1, 1).name("b")
+            solidRect(1, 1).name("c")
+            solidRect(1, 1).name("d")
+            solidRect(1, 1).name("e")
+        }
+
+        val removedCount = c.removeChildAt(0, 10)
+
+        assertEquals(5, removedCount)
+        assertEquals(0, c.children.size)
     }
 
     @Test