diff --git a/Terrain2/GameViewController.swift b/Terrain2/GameViewController.swift
index 8c531e1..1f51219 100644
--- a/Terrain2/GameViewController.swift
+++ b/Terrain2/GameViewController.swift
@@ -53,11 +53,13 @@ class GameViewController: NSViewController {
     }
 
     override func keyDown(with event: NSEvent) {
-        print("key down: \(String(describing: event.charactersIgnoringModifiers))")
         switch event.charactersIgnoringModifiers {
         case .some("n"):
             renderer.scheduleAlgorithmIteration()
+        case .some("z"):
+            renderer.drawLines = !renderer.drawLines
         default:
+            print("key down: \(String(describing: event.charactersIgnoringModifiers))")
             super.keyDown(with: event)
         }
     }
diff --git a/Terrain2/Renderer.swift b/Terrain2/Renderer.swift
index da0fb09..c98db1a 100644
--- a/Terrain2/Renderer.swift
+++ b/Terrain2/Renderer.swift
@@ -48,6 +48,8 @@ class Renderer: NSObject, MTKViewDelegate {
 
     var terrain: Terrain
 
+    var drawLines = true
+
     private var iterateTerrainAlgorithm = true
     private var didUpdateTerrain = false
 
@@ -271,7 +273,7 @@ class Renderer: NSObject, MTKViewDelegate {
                     
                     renderEncoder.setDepthStencilState(depthState)
 
-                    renderEncoder.setTriangleFillMode(.lines)
+                    renderEncoder.setTriangleFillMode(drawLines ? .lines : .fill)
                     
                     renderEncoder.setVertexBuffer(dynamicUniformBuffer, offset:uniformBufferOffset, index: BufferIndex.uniforms.rawValue)
                     renderEncoder.setFragmentBuffer(dynamicUniformBuffer, offset:uniformBufferOffset, index: BufferIndex.uniforms.rawValue)