diff --git a/Sources/AquaKit/General Purpose/Geometry/NSSize+Plus.swift b/Sources/AquaKit/General Purpose/Geometry/NSSize+Plus.swift
new file mode 100644
index 0000000..3225c92
--- /dev/null
+++ b/Sources/AquaKit/General Purpose/Geometry/NSSize+Plus.swift	
@@ -0,0 +1,7 @@
+import Foundation
+
+extension NSSize {
+	public static func + (lhs: NSSize, rhs: NSSize) -> NSSize {
+		NSSize(width: lhs.width + rhs.width, height: lhs.height + rhs.height)
+	}
+}
diff --git a/Sources/AquaKit/General Purpose/Geometry/Orientation.swift b/Sources/AquaKit/General Purpose/Geometry/Orientation.swift
new file mode 100644
index 0000000..45aed5e
--- /dev/null
+++ b/Sources/AquaKit/General Purpose/Geometry/Orientation.swift	
@@ -0,0 +1,40 @@
+import AppKit
+
+public enum Orientation {
+	case vertical
+	case horizontal
+}
+
+extension NSSize {
+	public subscript(orientation: Orientation) -> CGFloat {
+		get {
+			switch orientation {
+			case .vertical: height
+			case .horizontal: width
+			}
+		}
+		set {
+			switch orientation {
+			case .vertical: height = newValue
+			case .horizontal: width = newValue
+			}
+		}
+	}
+}
+
+extension NSPoint {
+	public subscript(orientation: Orientation) -> CGFloat {
+		get {
+			switch orientation {
+			case .vertical: y
+			case .horizontal: x
+			}
+		}
+		set {
+			switch orientation {
+			case .vertical: y = newValue
+			case .horizontal: x = newValue
+			}
+		}
+	}
+}
diff --git a/Sources/AquaKit/Scroll Views/AquaScrollState.swift b/Sources/AquaKit/Scroll Views/AquaScrollState.swift
new file mode 100644
index 0000000..f42aba0
--- /dev/null
+++ b/Sources/AquaKit/Scroll Views/AquaScrollState.swift	
@@ -0,0 +1,64 @@
+import Foundation
+import AppKit
+
+public struct AquaScrollState {
+	public var scrollPosition: NSPoint
+	public var contentSize: NSSize
+	public var visibleSize: NSSize
+	
+	public init(scrollPosition: NSPoint, contentSize: NSSize, visibleSize: NSSize) {
+		self.scrollPosition = scrollPosition
+		self.contentSize = contentSize
+		self.visibleSize = visibleSize
+	}
+
+	public var maxOffset: NSSize {
+		NSSize(
+			width: max(contentSize.width - visibleSize.width, 0),
+			height: max(contentSize.height - visibleSize.height, 0)
+		)
+	}
+
+	public var verticalOverscroll: CGFloat {
+		absoluteExcess(of: scrollPosition.y, in: 0..<maxOffset.height)
+	}
+
+	public func absoluteExcess(of position: CGFloat, in range: Range<CGFloat>) -> CGFloat {
+		if position < range.lowerBound {
+			range.lowerBound - position
+		} else if position > range.upperBound {
+			position - range.upperBound
+		} else {
+			0
+		}
+	}
+
+	public func absoluteExcess(of point: NSPoint, in size: NSSize) -> NSSize {
+		NSSize(
+			width: absoluteExcess(of: point.x, in: 0..<size.width),
+			height: absoluteExcess(of: point.y, in: 0..<size.height)
+		)
+	}
+
+	public var effectiveContentSize: NSSize {
+		contentSize + absoluteExcess(of: scrollPosition, in: maxOffset)
+	}
+}
+
+
+extension NSScroller {
+	public func adopt(state: AquaScrollState, orientation: Orientation) {
+		let maxOffset = state.maxOffset
+		let effectiveContentSize = state.effectiveContentSize
+		knobProportion = min(max(state.visibleSize[orientation] / effectiveContentSize[orientation], 0.0), 1.0)
+		doubleValue = maxOffset[orientation] > 0 ? min(max(state.scrollPosition[orientation] / maxOffset[orientation], 0.0), 1.0) : 0.0
+		isEnabled = maxOffset[orientation] > 0
+		isHidden = maxOffset[orientation] <= 0
+	}
+}
+
+extension AquaScroller {
+	public func adopt(state: AquaScrollState) {
+		adopt(state: state, orientation: orientation)
+	}
+}
diff --git a/Sources/AquaKit/Scroll Views/AquaScroller.swift b/Sources/AquaKit/Scroll Views/AquaScroller.swift
index d133779..cbc7801 100644
--- a/Sources/AquaKit/Scroll Views/AquaScroller.swift	
+++ b/Sources/AquaKit/Scroll Views/AquaScroller.swift	
@@ -2,10 +2,6 @@ import AppKit
 import AquaKit
 
 public class AquaScroller: NSScroller {
-	public enum Orientation {
-		case vertical, horizontal
-	}
-
 	public let orientation: Orientation
 
 	public override var floatValue: Float {
@@ -269,7 +265,7 @@ public class AquaScroller: NSScroller {
 	}
 }
 
-extension AquaScroller.Orientation {
+fileprivate extension Orientation {
 	/// The affine transform that maps between screen space and canonical (vertical)
 	/// coordinate space. For vertical this is the identity; for horizontal it swaps
 	/// the x and y axes. This transform is its own inverse.