Appendix E

Event Queues

Each window has an event queue, which is an ordinary Icon list. Pending() produces an event queue. An event is represented by three consecutive values on the list. The first value is the event code: a string for a keypress event or an integer for any other event. The next two values are Icon integers whose lower-order 31 bits are interpreted as fields having this format:

000 0000 0000 0SMC XXXX XXXX XXXX XXXX (second value)
EEE MMMM MMMM MMMM YYYY YYYY YYYY YYYY (third value)

The fields have these meanings:

   X...X    &x: 16-bit signed x-coordinate value
   Y...Y    &y: 16-bit signed y-coordinate value
   SMC      &shift, &meta, and &control flags
   E...M    &interval, interpreted as M^16E milliseconds
   0        unused; should be zero

Coordinate values do not reflect any translation specified by dx and dy attributes; the translation is applied by Event() when an event is read.

A malformed event queue error is reported if an error is detected when trying to read the event queue. Possible causes for the error include an event queue containing fewer than three values, or second or third entries that are not integer values or that are out of range. Only artificially constructed events can produce such errors.

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