diff --git a/Metaballs-macOS/ViewController.swift b/Metaballs-macOS/ViewController.swift
index 5d5e65c..1d6fd10 100644
--- a/Metaballs-macOS/ViewController.swift
+++ b/Metaballs-macOS/ViewController.swift
@@ -97,7 +97,20 @@ class ViewController: NSViewController, RendererDelegate {
     }
 
     override func keyDown(with event: NSEvent) {
-        print("key down: \(event)")
+        switch event.charactersIgnoringModifiers {
+        case .some("["):
+            let size = marchingSquares.sampleGridSize
+            if size.x > 2 {
+                marchingSquares.sampleGridSize = Size(size.x / 2)
+            }
+        case .some("]"):
+            let size = marchingSquares.sampleGridSize
+            if size.x < 32 {
+                marchingSquares.sampleGridSize = Size(size.x * 2)
+            }
+        default:
+            print("key down: \(event)")
+        }
     }
 
     override var acceptsFirstResponder: Bool {
diff --git a/MetaballsKit/MarchingSquares.swift b/MetaballsKit/MarchingSquares.swift
index 2f11d6e..8eefbb9 100644
--- a/MetaballsKit/MarchingSquares.swift
+++ b/MetaballsKit/MarchingSquares.swift
@@ -12,11 +12,18 @@ import simd
 
 class MarchingSquares {
     private var field: Field
-    private var sampleGridSize = Size(16)
+
+    var sampleGridSize = Size(16) {
+        didSet {
+            fieldDidResize()
+        }
+    }
 
     private var semaphore: DispatchSemaphore
 
+    /// Compute pipeline for sampling the field.
     private var samplingPipeline: MTLComputePipelineState?
+    /// Compute pipeline for calculating the contours based on a grid of samples.
     private var contouringPipeline: MTLComputePipelineState?
 
     private var parametersBuffer: MTLBuffer?