group widget and stack

src/main/kotlin/com/neptuneclient/voidui/framework/Widget.kt

@@ -179,4 +179,55 @@ abstract class LeafWidget : Widget() {
         voidUI.eventHandler.unregister(this)
     }
 
+}
+
+/**
+ * A special type of widget which contains multiple child widgets instead of just one.
+ */
+abstract class GroupWidget : Widget() {
+
+    /**
+     * The children of the group widget.
+     */
+    protected lateinit var roots: Array<Widget>
+
+    override fun init(screen: Screen, parent: Widget) {
+        this.voidUI = screen.voidUI
+        this.screen = screen
+
+        roots = buildGroup()
+        roots.forEach { it.init(screen, this) }
+    }
+
+    /**
+     * Since it is not clear how group widgets position their children, they need to define the layout themselves.
+     */
+    abstract override fun layout(constraints: BoxConstraints)
+
+    override fun postLayoutInit(parentOffset: Offset, parent: Widget) {
+        offset = parentOffset
+
+        val renderable = createRenderObject()
+        if (renderable != null)
+            screen.renderStack.push(renderable)
+
+        roots.forEach { it.postLayoutInit(parentOffset, this) }
+    }
+
+    override fun remove() {
+        roots.forEach { it.remove() }
+    }
+
+    /**
+     * Returns an array of widgets, which build the widget tree.
+     */
+    abstract fun buildGroup(): Array<Widget>
+
+    /**
+     * The build method from the widget is not called on group widgets.
+     */
+    override fun build(): Widget {
+        return Placeholder()
+    }
+
 }

src/main/kotlin/com/neptuneclient/voidui/widgets/Stack.kt

@@ -0,0 +1,32 @@
+package com.neptuneclient.voidui.widgets
+
+import com.neptuneclient.voidui.framework.BoxConstraints
+import com.neptuneclient.voidui.framework.GroupWidget
+import com.neptuneclient.voidui.framework.Size
+import com.neptuneclient.voidui.framework.Widget
+import kotlin.math.max
+
+/**
+ * A widget which layers multiple widgets on top of each other.
+ *
+ * @param children The array of children in the stack.
+ */
+class Stack(private val children: Array<Widget>) : GroupWidget() {
+
+    override fun layout(constraints: BoxConstraints) {
+        var childWidth = 0f
+        var childHeight = 0f
+
+        children.forEach {
+            it.layout(constraints)
+            childWidth = max(childWidth, it.size.width)
+            childHeight = max(childHeight, it.size.height)
+        }
+        size = constraints.constrain(Size(childWidth, childHeight))
+    }
+
+    override fun buildGroup(): Array<Widget> {
+        return children
+    }
+
+}

src/test/kotlin/com/neptuneclient/voidui/tests/ScreenTest.kt

@@ -6,7 +6,11 @@ import com.neptuneclient.voidui.VoidUI
 import com.neptuneclient.voidui.event.MouseClickedEvent
 import com.neptuneclient.voidui.event.MouseReleasedEvent
 import com.neptuneclient.voidui.framework.Screen
+import com.neptuneclient.voidui.framework.Size
 import com.neptuneclient.voidui.framework.Widget
+import com.neptuneclient.voidui.objects.Border
+import com.neptuneclient.voidui.objects.EdgeInsets
+import com.neptuneclient.voidui.utils.image
 import com.neptuneclient.voidui.widgets.*
 import org.junit.jupiter.api.condition.DisabledIfEnvironmentVariable
 import org.lwjgl.glfw.GLFW
@@ -15,7 +19,26 @@ import java.awt.Color
 class TestScreen(voidUI: VoidUI) : Screen(voidUI) {
 
     override fun build(): Widget {
-        return Placeholder()
+        return Container(
+            margin = EdgeInsets.all(100f),
+            border = Border(2f, Color.RED),
+            child = Stack(
+                children = arrayOf(
+                    Image(
+                        src = image("images/hampter.png"),
+                        imageSize = Size(
+                            width = 200f,
+                            height = 200f
+                        )
+                    ),
+                    Container(
+                        color = Color.GREEN,
+                        padding = EdgeInsets.symmetric(horizontal = 120f),
+                        child = Text("Hello World!")
+                    )
+                )
+            )
+        )
     }
 
 }