Swapped margin definitions of DockTop and DockBottom.

Author: bryanedds

Nu/Nu/World/WorldFacets.fs

@@ -2189,8 +2189,8 @@ type LayoutFacet () =
                     child.SetPositionLocal position.V3 world
                     child.SetSize size.V3 world
                 | DockTop ->
-                    let size = v2 perimeter.Width margins.W - margin
-                    let position = v2 0.0f (perimeterHeightHalf - margins.Z * 0.5f)
+                    let size = v2 perimeter.Width margins.Y - margin
+                    let position = v2 0.0f (-perimeterHeightHalf + margins.Y * 0.5f)
                     child.SetPositionLocal position.V3 world
                     child.SetSize size.V3 world
                 | DockRight ->
@@ -2199,8 +2199,8 @@ type LayoutFacet () =
                     child.SetPositionLocal position.V3 world
                     child.SetSize size.V3 world
                 | DockBottom ->
-                    let size = v2 perimeter.Width margins.Y - margin
-                    let position = v2 0.0f (-perimeterHeightHalf + margins.Y * 0.5f)
+                    let size = v2 perimeter.Width margins.W - margin
+                    let position = v2 0.0f (perimeterHeightHalf - margins.Z * 0.5f)
                     child.SetPositionLocal position.V3 world
                     child.SetSize size.V3 world
                 | DockLeft ->

Nu/Nu/World/WorldPrelude.fs

@@ -289,7 +289,7 @@ type Layout =
     /// Flow children in the given direcion up to the given limit.
     | Flow of FlowDirection : FlowDirection * FlowLimit : FlowLimit
 
-    /// Dock children using the given margins.
+    /// Dock children using the given margins (X = Left, Y = Top, Z = Right, W = Bottom).
     | Dock of Margins : Vector4 * PercentageBased : bool * ResizeChildren : bool
 
     /// Arrange children in a grid with the given dimensions, optional flow direction, and with optional resizing behavior.