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Source/Engine/UI/GUI/ScrollableControl.cs

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+// Copyright (c) 2012-2020 Wojciech Figat. All rights reserved.
+
+namespace FlaxEngine.GUI
+{
+    /// <summary>
+    /// Base class for container controls that can offset controls in a view (eg. scroll panels).
+    /// </summary>
+    /// <seealso cref="FlaxEngine.GUI.ContainerControl" />
+    [HideInEditor]
+    public class ScrollableControl : ContainerControl
+    {
+        /// <summary>
+        /// The view offset. Useful to offset contents of the container (used by the scrollbars and drop panels).
+        /// </summary>
+        protected Vector2 _viewOffset;
+
+        /// <summary>
+        /// Gets current view offset for all the controls (used by the scroll bars).
+        /// </summary>
+        [HideInEditor, NoSerialize]
+        public Vector2 ViewOffset
+        {
+            get => _viewOffset;
+            set => SetViewOffset(ref value);
+        }
+
+        /// <summary>
+        /// Sets the view offset.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        protected virtual void SetViewOffset(ref Vector2 value)
+        {
+            _viewOffset = value;
+            OnViewOffsetChanged();
+        }
+
+        /// <summary>
+        /// Called when view offset gets changed.
+        /// </summary>
+        protected virtual void OnViewOffsetChanged()
+        {
+        }
+
+        /// <inheritdoc />
+        protected override void DrawChildren()
+        {
+            // Draw all visible child controls
+            bool hasViewOffset = !_viewOffset.IsZero;
+            for (int i = 0; i < _children.Count; i++)
+            {
+                var child = _children[i];
+
+                if (child.Visible)
+                {
+                    Matrix3x3 transform = child._cachedTransform;
+                    if (hasViewOffset && child.IsScrollable)
+                    {
+                        transform.M31 += _viewOffset.X;
+                        transform.M32 += _viewOffset.Y;
+                    }
+
+                    Render2D.PushTransform(ref transform);
+                    child.Draw();
+                    Render2D.PopTransform();
+                }
+            }
+        }
+
+        /// <inheritdoc />
+        public override bool IntersectsChildContent(Control child, Vector2 location, out Vector2 childSpaceLocation)
+        {
+            // Apply offset on scrollable controls
+            if (child.IsScrollable)
+                location -= _viewOffset;
+
+            return child.IntersectsContent(ref location, out childSpaceLocation);
+        }
+
+        /// <inheritdoc />
+        public override bool IntersectsContent(ref Vector2 locationParent, out Vector2 location)
+        {
+            // Little workaround to prevent applying offset when performing intersection test with this scrollable control.
+            // Note that overriden PointFromParent applies view offset.
+            location = base.PointFromParent(ref locationParent);
+            return ContainsPoint(ref location);
+        }
+
+        /// <inheritdoc />
+        public override Vector2 PointToParent(ref Vector2 location)
+        {
+            return base.PointToParent(ref location) + _viewOffset;
+        }
+
+        /// <inheritdoc />
+        public override Vector2 PointFromParent(ref Vector2 location)
+        {
+            return base.PointFromParent(ref location) - _viewOffset;
+        }
+    }
+}