Adventure Game Studio

Whenever I try to run this script from repeatedly_execute, I get an error ("null pointer referenced"):

char prevAt = -1;

function dlgHighlight() {
  /* highlight the (complete) dialog option under the cursor */
  GUIControl* controlAt = GUIControl.GetAtScreenXY(mouse.x,  mouse.y);
  if (controlAt != null) {
    char objAt = 0;
    while ((objAt < 7) && (controlAt.ID != objAt)) { objAt++; }
    if (prevAt != -1) {
      if (objAt != prevAt) {
        gDialog.Controls[prevAt].AsLabel.TextColor = 31055; /* release previous item */
        gDialog.Controls[objAt].AsLabel.TextColor = 13; /* highlight current */
        prevAt = objAt; /* store item */
        }
      else {} /* still over previous item */
      }
    else { /* runs only once */
      gDialog.Controls[objAt].AsLabel.TextColor = 13; /* highlight current item */
      prevAt = objAt;
      }
    }
  else { /* null control - release all items*/
    char buf = 0;
    while (buf < 7) {
      gDialog.Controls[buf].AsLabel.TextColor = 31055;
      buf++;
      }
    }
  }

The problem is that

  if (controlAt != null) {
    char objAt = 0;
    while ((objAt < 7) && (controlAt.ID != objAt)) { objAt++; }

the "if (controlAt != null) {" line doesn't appear to be catching whether the pointer is actually null as the null pointer reference is a limit for the while loop.  Either that or somehow the only line in-between the two "char objAt = 0;" is causing the pointer to become null.  What is going on here?

Which line is the actual line number of the error?

The problem is on the line:

Edit:  The problem has moved from line 346 to line 349.  I made no changes since last night.

        gDialog.Controls[prevAt].AsLabel.TextColor = 31055; /* release previous item */

And the line that called it (374) (in repeatedly_execute()):

  dlgHighlight(); /* highlight dialog */

Quote from: Error Message---------------------------
Adventure Game Studio
---------------------------
An internal error has occured. Please note down the following information.
If the problem persists, contact Chris Jones.
(ACI version 2.70.856)

Error: run_text_script1: error -6 running function 'repeatedly_execute':
Error: Null pointer referenced
in Global script (line 349)
from Global script (line 374)


---------------------------
OK   
---------------------------

Last night the error was on line 346.  At least I thought it was...Perhaps I was just mistaken because I was tired.  I don't know.  I've edited the code...I don't know why I didn't just set objAt to the control ID in the first place, but this code makes more sense (doesn't solve the problem, just makes more sense):

char prevAt = -1;

function dlgHighlight() {
  /* highlight the (complete) dialog option under the cursor */
  GUIControl* controlAt = GUIControl.GetAtScreenXY(mouse.x,  mouse.y);
  if (controlAt != null) {
    char objAt = 0;
    objAt = controlAt.ID;
    if (prevAt != -1) {
      if (objAt != prevAt) {
        gDialog.Controls[prevAt].AsLabel.TextColor = 31055; /* release previous item */
        gDialog.Controls[objAt].AsLabel.TextColor = 13; /* highlight current */
        prevAt = objAt; /* store item */
        }
      else {} /* still over previous item */
      }
    else { /* runs only once per game -- initializes prevAt */
      gDialog.Controls[objAt].AsLabel.TextColor = 13; /* highlight current item */
      prevAt = objAt;
      }
    }
  else { /* null control -- release all items*/
    char buf = 0;
    while (buf < 7) {
      gDialog.Controls[buf].AsLabel.TextColor = 31055;
      buf++;
      }
    }
  }

There was no change in the line numbers, and I got the same error message.  I'll try commenting the line, but I don't know if it will help.

Edit:  Commenting the problem line prevented the error, but now the labels are not returned to their normal color (31055) until the controlAt parameter is null...

Edit:  Solved.

      if (objAt != prevAt) {
        if (gDialog.Controls[prevAt] != null)
         gDialog.Controls[prevAt].AsLabel.TextColor = 31055; /* release previous item */