ON TIMER(n) - QB64Official/qb64 GitHub Wiki

The ON_TIMER(n) statement sets up a timed event to be repeated at specified intervals throughout a program when enabled.

Syntax

ON TIMER(seconds%) GOSUB {lineLabel|lineNumber}

ON TIMER([number%,] seconds!) { SUBprocedure | GOSUB {lineLabel|lineNumber} }

Description

Legacy syntax

  • In the first syntax, the INTEGER seconds% parameter can be from 1 to 86400 seconds (one day).
  • A TIMER (statement) statement must follow an ON TIMER event setup to initiate it.
  • TIMER (statement) disables timer events but remembers previous events when enabled again by a TIMER (statement) statement, and the recorded events may be executed immediately if a timer event has occurred.
  • TIMER (statement) disables timer event trapping. Events will not be remembered in a subsequent TIMER (statement) statement.
  • ON TIMER events will interrupt a SLEEP call and RETURN to running program procedures.
  • Only one TIMER event can be set at a time using this legacy syntax and all TIMER code must be in the main code, as it uses GOSUB.

QB64 syntax

  • QB64 can use multiple numbered timer events and SINGLE floating point second values down to one millisecond (.001).
  • The TIMER number% must be obtained from the _FREETIMER function. Store _FREETIMER numbers in a variable or an array to be able to reference them later.
  • If the TIMER number is omitted or **ON TIMER**(0, seconds!) is used, then the TIMER used is the base TIMER (same as in the legacy syntax above).
  • SUB procedures are allowed to be referenced, but CALL must not be used.
  • SUB parameter values are passed by value and should be SHARED or literal values.
  • Specific TIMER events can be turned on, suspended, turned off or freed using TIMER (statement) ON, STOP, OFF or FREE.
  • Use TIMER(n) FREE to release a timer event after it has been turned off or is no longer used.
    • The base TIMER cannot be freed.
  • QB64 allows TIMER statements to also be inside of SUB and FUNCTION procedures.
  • ON TIMER events will interrupt a SLEEP call and RETURN to running program procedures.
  • $CHECKING:OFF can disable all QB64 event checking. Setting $CHECKING:OFF is only designed for 100% stable, error-less sections of code, where every CPU cycle saved counts.

QB64 Timing Alternatives

  • The TIMER function can be used to find timed intervals down to 1 millisecond(.001) accuracy.
  • The _DELAY statement can be used to delay program execution for intervals down to milliseconds.
  • _LIMIT can slow down loops to a specified number of frames per second. This can also alleviate a program's CPU usage.

Example(s)

Using a numbered TIMER to check the mouse button press status in QB64.


DIM SHARED Button AS LONG    'share variable value with Sub

t1 = _FREETIMER              'get a timer number from _FREETIMER ONLY!
ON TIMER(t1, .05) MouseClick
TIMER(t1) ON

DO
  LOCATE 1, 1
  IF Button THEN
    PRINT "Mouse button"; Button; "is pressed.";
  ELSE PRINT SPACE$(70)
  END IF
  _DISPLAY
LOOP UNTIL INKEY$ = CHR$(27)
TIMER(t1) OFF
TIMER(t1) FREE 'release timer
END

SUB MouseClick
DO WHILE _MOUSEINPUT
  IF _MOUSEBUTTON(1) THEN
    COLOR 10: Button = 1
  ELSEIF _MOUSEBUTTON(2) THEN
    COLOR 12: Button = 2
  ELSE Button = 0
  END IF
LOOP
END SUB

See Also