rudimentary undo functionality

pixler.bas

@@ -140,6 +140,16 @@ do
             showcolorpicker=not showcolorpicker
         case "l"
             showcommands=not showcommands
+        case chr$(26) ' Ctrl+Z
+            if ubound(commands) > 3 then
+                ' Drop the trailing empty slot AND the last valid command
+                redim _preserve commands(ubound(commands) - 2) as string
+                
+                ' Re-create the empty trailing slot required by addcommand
+                redim _preserve commands(ubound(commands) + 1) as string
+                
+                redraw             
+            end if
     end select
 
     ' 4. Draw everything using the freshly updated math