diff --git a/Shared/History.cs b/Shared/History.cs
index 1835f98..50fcbcb 100644
--- a/Shared/History.cs
+++ b/Shared/History.cs
@@ -51,6 +51,7 @@ namespace SemiColinGames {
     }
 
     // This creates and populates a new array. It's O(n) and should probably only be used for tests.
+    // TODO: restrict visibility so that it can only be used by tests.
     public T[] ToArray() {
       T[] result = new T[items.Length];
       for (int i = 0; i < items.Length; i++) {
diff --git a/Shared/Line.cs b/Shared/Line.cs
index 03446cd..2dcf8de 100644
--- a/Shared/Line.cs
+++ b/Shared/Line.cs
@@ -22,6 +22,7 @@ namespace SemiColinGames {
       int errorXY;  // Error value e_xy from the PDF.
       // The size of the output is the size of the longer dimension, plus one.
       int resultSize = Math.Max(dx, -dy) + 1;
+      // TODO: an array or list should be passed in by the caller.
       var result = new Point[resultSize];
 
       int i = 0;
diff --git a/Shared/Player.cs b/Shared/Player.cs
index c0fa3e3..379c926 100644
--- a/Shared/Player.cs
+++ b/Shared/Player.cs
@@ -83,6 +83,8 @@ namespace SemiColinGames {
       }
 
       bool harmedByCollision = false;
+      // TODO: pass in movePoints to Line.Rasterize instead of having that function allocate a
+      // new array.
       Point[] movePoints = Line.Rasterize(0, 0, (int) movement.X, (int) movement.Y);
       for (int i = 1; i < movePoints.Length; i++) {
         int dx = movePoints[i].X - movePoints[i - 1].X;