version 13/130803 by Jon Ingold
Section: Window Rules
When a window is opened or redrawn, the window-drawing rules for that window are consulted. The window-drawing rule should (ideally) be able to reconstruct entirely the contents of the window (otherwise, after an UNDO or a RESTORE, information will be lost). Rules for graphical drawing will want to use glk calls to place images--see Simple Graphical Window for examples.
Text windows are supplied with three important phrases: one to move the focus to a different window, one to clear that window (if required), and one to shift the focus back. A drawing rule for a window designed to display the player's inventory would use all three, and take the following form:
A window-drawing rule for the side-window (this is the display inventory in side-window rule):
move focus to side-window, clearing the window;
try taking inventory;
return to main screen;
Any text window can be cleared at any time using
Note that Version 9's handling of drawing rules is different from earlier versions', and will require some changes to existing source code:
1) The "drawing rule" property for windows no longer exists. References to this property should be removed.
2) The rule preamble for drawing rules should be changed to the form:
A window-drawing rule for the side-window
3) Specific invocations of drawing rules should be changed to read as follows:
follow the window-drawing rules for the side-window