ON TIMER(n): Difference between revisions

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=== Legacy syntax ===
=== Legacy syntax ===
* In the first syntax, the [[INTEGER]] {{Parameter|seconds%}} parameter can be from 1 to 86400 seconds (one day).
* In the first syntax, the [[INTEGER]] {{Parameter|seconds%}} parameter can be from 1 to 86400 seconds (one day).
* A [[TIMER (statement)|TIMER ON]] statement must follow an '''ON TIMER''' event setup to initiate it.
* A [[TIMER|TIMER ON]] statement must follow an '''ON TIMER''' event setup to initiate it.
* [[TIMER (statement)|TIMER STOP]] disables timer events but remembers previous events when enabled again by a [[TIMER (statement)|TIMER ON]] statement, and the recorded events may be executed immediately if a timer event has occurred.
* [[TIMER|TIMER STOP]] disables timer events but remembers previous events when enabled again by a [[TIMER|TIMER ON]] statement, and the recorded events may be executed immediately if a timer event has occurred.
* [[TIMER (statement)|TIMER OFF]] disables timer event trapping. Events will not be remembered in a subsequent [[TIMER (statement)|TIMER ON]] statement.
* [[TIMER|TIMER OFF]] disables timer event trapping. Events will not be remembered in a subsequent [[TIMER|TIMER ON]] statement.
* '''ON TIMER''' events will interrupt a [[SLEEP]] call and [[RETURN]] to running program procedures.
* '''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]].
* 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]].
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* [[SUB]] procedures are allowed to be referenced, but [[CALL]] must not be used.
* [[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.'''
* '''[[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)|TIMER(n)]] ON, STOP, OFF or FREE.
* Specific '''TIMER''' events can be turned on, suspended, turned off or freed using [[TIMER|TIMER(n)]] 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.
* 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.
** The ''base TIMER'' cannot be freed.
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== QB64 Timing Alternatives ==
== QB64 Timing Alternatives ==
* The [[TIMER]] function can be used to find timed intervals down to 1 millisecond(.001) accuracy.
* 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.
* 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.
* [[_LIMIT]] can slow down loops to a specified number of frames per second. This can also alleviate a program's CPU usage.
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{{Cl|DIM}} {{Cl|SHARED}} Button {{Cl|AS}} {{Cl|LONG}}    'share variable value with Sub
{{Cl|DIM}} {{Cl|SHARED}} Button {{Cl|AS}} {{Cl|LONG}}    'share variable value with Sub


t1 = _{{Cl|TIMER (statement)|FREE}}{{Cl|TIMER}}              'get a timer number from _FREETIMER ONLY!
t1 = {{Cl|_FREETIMER}}              'get a timer number from _FREETIMER ONLY!
{{Cl|ON TIMER(n)|ON TIMER}}(t1, .05) MouseClick
{{Cl|ON TIMER(n)|ON TIMER}}(t1, .05) MouseClick
{{Cl|TIMER}}(t1) ON
{{Cl|TIMER}}(t1) ON
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{{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|INKEY$}} = {{Cl|CHR$}}(27)
{{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|INKEY$}} = {{Cl|CHR$}}(27)
{{Cl|TIMER}}(t1) {{Cl|OFF}}
{{Cl|TIMER}}(t1) {{Cl|OFF}}
{{Cl|TIMER}}(t1) {{Cl|TIMER (statement)|FREE}} 'release timer
{{Cl|TIMER}}(t1) FREE 'release timer
{{Cl|END}}
{{Cl|END}}


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{{PageSeeAlso}}
{{PageSeeAlso}}
* [[TIMER]], [[_FREETIMER]]
* [[_FREETIMER]], [[TIMER]]
* [[TIMER (statement)]], [[_DELAY]], [[_LIMIT]]
* [[_DELAY]], [[_LIMIT]]
* [[$CHECKING]] {{text|(QB64 [[Metacommand]])}}
* [[$CHECKING]]




{{PageNavigation}}
{{PageNavigation}}

Latest revision as of 16:59, 24 February 2023

The ON TIMER 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 ON statement must follow an ON TIMER event setup to initiate it.
  • TIMER STOP disables timer events but remembers previous events when enabled again by a TIMER ON statement, and the recorded events may be executed immediately if a timer event has occurred.
  • TIMER OFF disables timer event trapping. Events will not be remembered in a subsequent TIMER ON 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(n) 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.


Examples

Example: 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


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