diff --git a/demo2.cpp b/demo2.cpp
index 3a1354b..0b4734d 100644
--- a/demo2.cpp
+++ b/demo2.cpp
@@ -974,6 +974,10 @@ int16_t intensity = 0;
 #endif
 
 #ifndef NO_SHADING
+    /* NOTE: to gain a lot of performance, it's best to have precomputed color
+       color gradients and look the colors up as opposed to calling
+       addIntensity(...), but for the sake of simplicity we don't do it
+       here. */
     if (previousColumn == pixel->position.x)
     {
       color = addIntensity(color,pixelIntensity);