In Glk, what happens to the cursor when text grid windows resize?

Technical Development Specifications
1

Section 3.5.4 of the Glk specification document describes “text grid windows”, which store an “output cursor position”. Consider the following 16x4 text grid window, where the cursor (represented by _) is at (13, 1):

+----------------+
|This is a text w|
|indow...     _  |
|                |
|                |
+----------------+

The window is resized to 8x4:

+--------+
|This is |
|indow...|    _  <- (13, 1) is now out of bounds!
|        |
|        |
+--------+

What happens to the cursor? The specification doesn’t seem to say, and I can come up with a few different plausible ideas:

  • It moves to (0, 2), the beginning of the next line
  • It moves to (5, 2), which is where it would be if it started at (0, 1) and 13 characters were printed
  • It moves to (5, 3), which is where it would be if it started at (0, 0) and 16+13=29 characters were printed
  • It is reset to (0, 0)
  • It goes “off the screen”, silencing all further output until it’s put back in bounds with a glk_window_move_cursor() or glk_window_clear() call
2 Likes
2

Good question. My guess is that the last option, that it goes off the screen, would be the most consistent, though it’s highly possible implementations do something else instead.

3

The official answer is “the spec doesn’t say, therefore don’t rely on the cursor position staying the same after a resize input event.” (Or, really, any input event.)

What I remember implementing (RemGlk, Quixe) is that it goes off-screen. But the interpreter checks it back on-screen the next time text is printed, using the “wrap to beginning of the next line” rule. If there aren’t enough lines, further output is silenced.

However, I may be remembering this wrong, and I haven’t looked at what other implementations do.

2 Likes