{{DISPLAYTITLE:_GL}}
In order to use OpenGL drawing commands, you must do so from inside a [[SUB]] procedure called '''_GL''', which enables the commands to be rendered.


{{PageSyntax}}
:[[SUB]] _GL
:: ''REM Your OpenGL code here
: [[END]] [[SUB]]

{{PageDescription}}
* OpenGL commands are valid outside of '''SUB _GL''', as long as the sub procedure exists in your code.
* Attempting to use OpenGL commands without having '''SUB _GL''' in a program will result in a '''Syntax error''', even if the syntax is valid.
* SUB '''_GL''' cannot be invoked manually. The code inside it will be called automatically at approximately 60 frames per second.
* Using [[INPUT]] inside SUB '''_GL''' will crash your program.
* If your program needs to perform any operations before SUB _GL must be run, it is recommended to use a shared variable as a flag to allow SUB _GL's contents to be run. See example below.


==Example==

{{CodeStart}} '' ''
{{Cl|DIM}} allowGL {{Cl|AS}} {{Cl|_BYTE}}

'perform startup routines like loading assets

allowGL = -1 'sets allowGL to true so SUB _GL can run

{{Cl|DO}}
    {{Cl|_LIMIT}} 1 'runs the main loop at 1 cycle per second
    'notice how the main loop doesn't do anything, as SUB _GL will be running
    'continuously.
{{Cl|LOOP}}

{{Cl|SUB}} {{Cl|_GL}}
    {{Cl|IF}} NOT allowGL {{Cl|THEN}} {{Cl|EXIT}} {{Cl|SUB}} 'used to bypass running the code below until
    '                             startup routines are done in the main module

    'OpenGL code starts here
    'The code in this area will be run automatically at ~60fps
{{Cl|END}} {{Cl|SUB}} '' ''
{{CodeEnd}}


{{PageSeeAlso}}
* [[http://www.qb64.org/wiki/Keyword_Reference_-_Alphabetical#glA List of OpenGL commands]] ''All commands in the list are valid. For those without a wiki page, usage follows OpenGL standards.''
* [[SUB]]


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