Use RgbaColorRenderer for selection box rendering.

OpenRA.Game/Widgets/WorldInteractionControllerWidget.cs

@@ -53,7 +53,8 @@ namespace OpenRA.Widgets
 
 			// Render actors in the dragbox
 			var selbox = SelectionBox;
-			Game.Renderer.WorldLineRenderer.DrawRect(selbox.Value.First.ToFloat2(), selbox.Value.Second.ToFloat2(), Color.White);
+			Game.Renderer.WorldRgbaColorRenderer.DrawRect(selbox.Value.First, selbox.Value.Second,
+				1 / worldRenderer.Viewport.Zoom, Color.White);
 			foreach (var u in SelectActorsInBoxWithDeadzone(World, selbox.Value.First, selbox.Value.Second))
 				DrawRollover(u);
 		}